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Lab-on-a-robot: Integrated microchip CE, power supply, electrochemical detector, wireless unit, and mobile platform
Abstract
In this paper, the fabrication of a wireless mobile unit containing an electrochemical detection module and a 3-channel high-voltage power supply (HVPS) designed for microchip CE is described. The presented device consists of wireless global positioning system controlled robotics, an electrochemical detector utilizing signal conditioning analog circuitry and a digital feedback range controller, a HVPS, an air pump, and a CE microchip. A graphical user interface (LabVIEW) was also designed to communicate wirelessly with the device, from a distant personal computer communication port. The entire device is integrated and controlled by digital hardware implemented on a field programmable gate array development board. This lab-on-a-robot is able to navigate to a global position location, acquire an air sample, perform the analysis (injection, separation, and detection), and send the data (electropherogram) to a remote station without exposing the analyst to the testing environment.
... 25,26 Depending on what analytes of interest are, CE and ME is supplied with different detectors: (a) uorescence, (b) contactless conductivity, (c) electrochemical. 19,20,[27][28][29][30][31] Depending on the application, use-cases of portable CE instruments range from point-of-care analysis to the detection of explosives and other potentially hazardous compounds. 12,21,[32][33][34][35][36] Some attempts to design and apply autonomous analytical systems have been performed. ...
... A lab-on-a-robot system containing an electrochemical detector, microchip electrophoresis, and sampling units have been integrated into a remotely controlled mini-rover platform. 28 Aer the outbreak of Ebola, a lab-on-a-drone system supplied with a polymerase chain reaction analytical module was demonstrated. 37 Another unmanned long-range roverplatform containing an integrated capillary electrophoresis unit with contactless conductivity detector (C4D), designed for determination of nerve agents has been demonstrated. ...
... The lab-on-a-robot microchip CE version had electrokinetic injection capability. 28 Breadmore's group utilized dualchannel sequential injection for microchip electrophoresis that resulted in a small instrument. 24 Hauser's group utilized a miniature syringe Labsmith pump in their breadboard CE version. ...
Hazardous remote places exist in the world. Why should health or life be risked sending a scientist to the investigation site, as the remote analytical instrumentation exists? Different scientific fields require instruments that could be used on-site (in situ), therefore the purpose of this work was to design a fully automated chemical analysis system small enough to be mountable on a drone. Here we show an autonomous analytical system with sampling capability on a drone. The system is suited for the remote and autonomous analysis of volatile and non-volatile chemicals in the air. The designed system weighs less than 800 g. Data are transmitted wirelessly. Collected substances are separated automatically without the intervention of the operator using the method of capillary zone electrophoresis. The analytes are detected using a miniaturized contactless conductivity detector quantifying them down to less than 1 μM. In this work, we demonstrated sampling and separation of volatile amines (triethylamine and diethylamine) and organic acids (acetic and formic acids), non-volatile inorganic cations (K⁺, Ca²⁺, Na⁺), and protein (bovine serum albumin) in the aerosol state. It was shown that the capillary electrophoretic analysis can be performed on a hovering drone. We anticipate our work to be a starting point for more sophisticated, autonomous complex sample analysis. We believe that our designed instrument will enable the investigation of hazardous places in different research fields.
... 25,26 Depending on what analytes of interest are, CE and ME is supplied with different detectors: (a) uorescence, (b) contactless conductivity, (c) electrochemical. 19,20,[27][28][29][30][31] Depending on the application, use-cases of portable CE instruments range from point-of-care analysis to the detection of explosives and other potentially hazardous compounds. 12,21,[32][33][34][35][36] Some attempts to design and apply autonomous analytical systems have been performed. ...
... A lab-on-a-robot system containing an electrochemical detector, microchip electrophoresis, and sampling units have been integrated into a remotely controlled mini-rover platform. 28 Aer the outbreak of Ebola, a lab-on-a-drone system supplied with a polymerase chain reaction analytical module was demonstrated. 37 Another unmanned long-range roverplatform containing an integrated capillary electrophoresis unit with contactless conductivity detector (C4D), designed for determination of nerve agents has been demonstrated. ...
... The lab-on-a-robot microchip CE version had electrokinetic injection capability. 28 Breadmore's group utilized dualchannel sequential injection for microchip electrophoresis that resulted in a small instrument. 24 Hauser's group utilized a miniature syringe Labsmith pump in their breadboard CE version. ...
The development of the instrument which will significantly ease the in situ samplings of volatile compounds is described. The purpose of this work was to design an automated, portable, handheld sample collection device that operates with monolithic adsorbents. The sampler contains two lithium-ion batteries, collects samples into micro-liter range volume vials, is supplied with a changeable 100 µm inner diameter six cm long capillary with an in-tube monolithic solid-phase micro-extraction adsorbent. Modeling experiments with triethylamine and diethylamine demonstrated that instrument captured samples containing volatile substances in the range of 3.5 to 118 ppm concentration levels in the air. The substances have been analyzed using a dedicated capillary electrophoresis contactless conductivity detection system and determined amounts of volatile substances in the sample solutions ranged between 3.4 and 1010 µM. Only 0.44 mL of air was enough to adsorb substances on the adsorbent, collecting them into 50 µL of water and achieving a preconcentration effect. The developed instrument is expected to find it’s applications where sampled air or gas volume is in µL – mL range: (a) collection of volatile substances near single plant parts in vivo, (b) collection of beetle pheromones in vivo, (c) volume-restricted machinery and other related applications.
... Skelley et al. presented a microfabricated CE instrument called the Mars Organic Analyzer (MOA) capable of determining key biomarkers present in Mars-like soil samples (Skelley et al., 2005). The MOA showed a weight of 11 kg and a peak power utilization of 15 W. The concept of lab-on-a-robot was introduced in 2008 by Berg et al. to carry out remote wireless analysis (Berg et al., 2008). This system consisted of the combination of a chip-based CE system, a mobile platform and wireless global position system (GPS) (Figure 1.9). ...
... Picture of the assembled lab-on-a-robot containing high-voltage power supply, electrochemical detector, mobile platform, field programmable gate array, radio frequency modem, compass, and GPS. Reprinted fromBerg et al. (2008) with permission from John Wiley & Sons. ...
1.1 Introduction Nowadays, the term miniaturization is applied to a wide spectrum of knowledge areas, including, among others, engineering, physics, medicine, materials science, com-puter science and chemistry. A search on the ISI Web of Knowledge provided approxi-mately 42000 results by entering the term miniaturization, from which around 5200 results are devoted to chemistry. The number of publications concerning the min-iaturization of chemical systems has experienced an important increase in the last two decades, as has the number of citations received by these publications, as shown in Figure 1.1. In accordance with the ISI Web of Knowledge, they currently receive around 12000 citations per year. Nevertheless, this is only the tip of the iceberg since the number of publications devoted to the development and application of miniatur-ized analytical systems (but not referring to miniaturization in the title or abstract sections) are not included. In the broadest sense of the word, miniaturization can be defined as the produc-tion of novel systems that are substantially reduced in size in comparison with con-ventional systems. In analytical chemistry, the term miniaturization does not refer solely to the scaling-down of analytical instrumentation, apparatus and devices since it is also applicable when the components (including chemicals and solvents) needed to perform analytical operations are employed on a greatly reduced scale. In fact, size reduction is not the main driving force when shrinking analytical systems, as can be deduced from section 1.2. It is worth noting that the term miniaturization has been mainly employed in the analytical chemistry literature to refer to the micro-total anal-ysis systems (µ-TAS) and lab-on-a-chip (LOC) devices. Even though they represent the highest degree of downsizing, the concept of miniaturization should be observed from a broader, non-exclusive perspective since this concept includes the advances achieved in every single step of the analytical process. A recent trend in analytical chemistry is a progression towards the miniaturiza-tion of analytical systems. Different steps of the analytical process, including sample preparation, analytical separation and detection have been subjected to miniaturiza-tion, automation and portability. In addition, the integration of different analytical steps has allowed the development of fully miniaturized systems. The
... Recently it can be observed that the interest in 3D printing technology for manufacturing of flow chip and equipment has been growing [28][29][30][31]. Described technology (lab-on-a-chip) can be extended to the mobile platform (lab-on-a-robot) [26,32,33]. More recently, the first integrated system capable of performing remote analysis of air samples using microchip-CE was presented [33]. ...
... Described technology (lab-on-a-chip) can be extended to the mobile platform (lab-on-a-robot) [26,32,33]. More recently, the first integrated system capable of performing remote analysis of air samples using microchip-CE was presented [33]. The screenprinted electrodes (SPEs) can be used as a suitable detectors in CE microchips [34]. ...
Remote-controlled robotic systems are being used for analysis of various types of analytes in hostile environment including those called extra-terrestrial. The aim of our study was to develop a remote-controlled robotic platform (ORPHEUS-HOPE) for bacterial detection. For the platform ORPHEUS-HOPE a 3D printed flow chip was designed and created with a culture chamber volume 600 μl. The flow rate was optimized to 500 μl.min−1. The chip was tested primarily for detection of 1-naphthol by differential pulse voltammetry with detection limit (S/N = 3) as 20 nM. Further, the way how to capture bacteria was optimized. To capture bacterial cells (Staphylococcus aureus), maghemite nanoparticles (1 mg ml−1) were prepared and modified with collagen, glucose, graphene, gold, hyaluronic acid and graphene with gold or graphene with glucose (20 mg ml−1). The most up to 50% of the bacteria were captured by graphene nanoparticles with glucose. The detection limit of the whole assay, which included capturing of bacteria and their detection under remote control operation, was estimated as 30 bacteria per μl.
... Therefore, detector miniaturization and power consumption reduction are of critical importance in modern science. Particular attention should be paid to lab-on-a-robot [12] or planetary rover [13,14] detection systems due to their special requirements for power consumption and size. Also unmanned platforms for longrange remote analysis would greatly benefit from smaller size implemented instrumentation [15]. ...
... In addition, signal sensing, conditioning, and acquisition circuitry can add significant values to power consumption. In comparison to LEDIF, electrochemical detectors can be smaller in size and more efficient in power consumption [10][11][12]. However, such detection technique is often limited to a reduced number of compounds with native electrochemical activity. ...
A capacitance-to-digital converter integrated circuit was implemented in an automated capillary electrophoresis device as a single chip detector. In this paper, design and hardware issues related to the fabrication and application of a miniature detector for contactless measurement of complex impedance are discussed. The capacitance-to-digital converter integrated circuit was used as the whole detector. The advantage of this setup is that the single integrated circuit provides digital data and neither additional signal conditioning nor analog-to-digital converter is required. Different separation conditions were used to evaluate the detection characteristics of the constructed detection unit. A 1 μM limit of detection for sodium and a 1.6 μM limit of detection for potassium ions were revealed for the detector. The detection system designed is competitive with miniaturized contactless conductivity detectors or UV absorbance detectors with respect to overall parameters (sensitivity, resolution, power consumption properties and size). The obtained separation and detection results show that such detection technique can be used as an extremely low power consuming and space saving solution for capillary electrophoresis detection with potential applications in environmental monitoring, process control and various analytical measurements. This article is protected by copyright. All rights reserved
... The concept of lab-on-a-robot was discussed by Berg et al [98]. Their system is a wireless mobile unit fitted with a global positioning system, capable of navigating to a location, acquiring a gaseous sample, performing CE and sending the data to a remote station. ...
... Photograph of the lab-on-a-robot system. Reprinted with permission from[98]. Copyright (2008) John Wiley and Sons. ...
Capillary electrophoresis (CE) is a technique which uses an electric field to separate a mixed sample into its constituents. Portable CE systems enable this powerful analysis technique to be used in the field. Many of the challenges for portable systems are similar to those of autonomous in-situ analysis and therefore portable systems may be considered a stepping stone towards autonomous in-situ analysis. CE is widely used for biological and chemical analysis and example applications include: water quality analysis; drug development and quality control; proteomics and DNA analysis; counter-terrorism (explosive material identification) and corrosion monitoring. The technique is often limited to laboratory use, since it requires large electric fields, sensitive detection systems and fluidic control systems. All of these place restrictions in terms of: size, weight, cost, choice of operating solutions, choice of fabrication materials, electrical power and lifetime. In this review we bring together and critique the work by researchers addressing these issues. We emphasize the importance of a holistic approach for portable and in-situ CE systems and discuss all the aspects of the design. We identify gaps in the literature which require attention for the realization of both truly portable and in-situ CE systems.
... The main goal for the development of LOC systems consists on the miniaturization of each part of the instruments without compromising their functionality. Highvoltage power supplies (HVPS) [33,34], electrochemical detectors [35][36][37] (potentiostats and conductimeters), and also wireless communications are available in small designs that allow them to fit together in a highly integrated and portable instrument [38,39]. In the last year, portable instruments and reviews of them have been also described [5,40,41]. ...
... In addition, sample storage step, which involves possible chemical decomposition, high cost, and time of analysis, is eliminated. A wireless mobile unit, called "labon-a-robot", has been used to perform environmental analysis [39]. Recently, an unattended water sensor (UWS) prototype has been designed to detect proteins biotoxins [8] from domestic water flow. ...
A second generation of a battery-powered portable electrophoresis instrument for the use of ME with electrochemical detection was developed. As the first-generation, the main unit of the instrument (150 mm × 165 mm × 95 mm) consists of four-outputs high-voltage power supply (HVPS) with maximum voltage of 3 KV and acquisition system (bipotentiostat) containing 2-channels for dual electrochemical detection. A new reusable microfluidic platform was designed in order to incorporate the microchips with the portable instrument. In this case, the platform is integrated to the main unit of the instrument so that it is not necessary to have any external cable for the interconnection of both parts, making the use of the complete system easier. The new platform contains all the electrical connections for the HVPS and bipotentiostat, as well as fluidic ports for driving the solutions. The microfluidic electrophoresis instrument is controlled by means of a user-friendly interface from a computer. The possibility of wireless connection (Bluetooth®) allows the use of the instrument without any external cable improving the portability. Therefore, the second generation brings a more compact and integrated electrophoresis instrument for "in situ" applications using microfluidic chips in an easy way. The performance of the electrophoresis system was initially evaluated using single- and dual-channel SU-8/Pyrex microchips with different models of integrated electrodes including microelectrodes and interdigitated arrays. The method was tested in different analytical applications such as separation of neurotransmitters, chlorophenols, purine derivatives, vitamins, polyphenolic acids, and flavones.
... Amperometry is a popular detection method for lab-on-a-chip devices due to its high sensitivity and selectivity as well as the fact that electrodes can be fabricated using the same photolithographic techniques employed to create the microfluidic device [1][2][3]. ME is a technique that is able to generate very fast, highly efficient separations in a small and potentially portable format [3][4][5][6]. The combination of amperometric detection with ME provides a powerful approach to the determination of a variety of biologically important compounds including reactive oxygen species (ROS) [7], reactive nitrogen species (RNS) [8], catecholamines [9,10], thiols [11,12], and carbohydrates [13][14][15]. ...
... This attribute will be especially useful in applications in which the analytical device is in a different location than the analyst. Examples include remote sensing of hazardous substances [5,6], point-of-care testing in Third World countries and separation-based sensors for on-animal monitoring of neurotransmitters [4,6]. ...
The combination of microchip electrophoresis with amperometric detection leads to a number of analytical challenges that are associated with isolating the detector from the high voltages used for the separation. While methods such as end-channel alignment and the use of decouplers have been employed, they have limitations. A less common method has been to utilize an electrically isolated potentiostat. This approach allows placement of the working electrode directly in the separation channel without using a decoupler. This paper explores the use of microchip electrophoresis and electrochemical detection with an electrically isolated potentiostat for the separation and in-channel detection of several biologically important anions. The separation employed negative polarity voltages and tetradecyltrimethylammonium bromide (as a buffer modifier) for the separation of nitrite (NO₂⁻), glutathione, ascorbic acid, and tyrosine. A half-wave potential shift of approximately negative 500 mV was observed for NO₂⁻ and H₂O₂ standards in the in-channel configuration compared to end-channel. Higher separation efficiencies were observed for both NO₂⁻ and H₂O₂ with the in-channel detection configuration. The limits of detection were approximately two-fold lower and the sensitivity was approximately two-fold higher for in-channel detection of nitrite when compared to end-channel. The application of this microfluidic device for the separation and detection of biomarkers related to oxidative stress is described.
... In addition, sample storage step, which involves high cost and time of analysis, is eliminated. Recently, a wireless mobile unit, called lab-on-a-robot, has been used to perform environmental analysis [45]. Portable CE instruments with amperometric, potentiometric, and conductivity detection have been also described [46][47][48][49][50]. ...
... In other cases, miniaturized HVPS with several channels has been designed, but this did not include the acquisition system that in many cases is not miniaturized, making a nonportable instrumentation [53][54][55][56]. The most promised instrument development has been presented by García et al. [45], which incorporates in the same instrument a three-channel HVPS, a electrochemical detector, a global positioning system, an air pump, and a MCE. However, the HVPS is limited to 2000 V and a holder for easy -handling of different microchip designs is not included. ...
A new portable instrument that includes a high voltage power supply, a bipotentiostat, and a chip holder has been especially developed for using microchips electrophoresis with electrochemical detection. The main unit of the instrument has dimensions of 150 x 165 x 70 mm (wxdxh) and consists of a four-outputs high voltage power supply with a maximum voltage of +/-3 KV and an acquisition system with two channels for dual amperometric (DC or pulsed amperometric detection) detection. Electrochemical detection has been selected as signal transduction method because it is relatively easily implemented, since nonoptical elements are required. The system uses a lithium-ion polymer battery and it is controlled from a desktop or laptop PC with a graphical user interface based on LabVIEW connected by serial RS232 or Bluetooth. The last part of the system consists of a reusable chip holder for housing the microchips, which contain all the electrical connections and reservoirs for making the work with microchips easy. The performance of the new instrument has been evaluated and compared with other commercially available apparatus using single- and dual-channel pyrex microchips for the separation of the neurotransmitters dopamine, epinephrine, and 3,4-dihydroxy-L-phenyl-alanine. The reduction of the size of the instrument has not affected the good performance of the separation and detection using microchips electrophoresis with electrochemical detection. Moreover, the new portable instrument paves the way for in situ analysis making the use of microchips electrophoresis easier.
... The work published by Berg et al. described the development of a wireless mobile unit containing an electrochemical detection module and a 3-channel high-voltage power supply designed for microchip CE; the device can be integrated and controlled by digital hardware. The lab-on-a-robot device has been used to navigate a global position, acquire an air sample, perform the analysis, and send the data to a remote location [59]. ...
Wireless chemical sensors have been developed as a result of advances in chemical sensing and wireless communication technology. Because of their mobility and widespread availability, smartphones have been extensively combined with sensors such as hand-held detectors, sensor chips, and test strips for biochemical detection. Smartphones are frequently used as controllers, analyzers, and displayers for quick, authentic, and point-of-care monitoring, which may considerably streamline the design and lower the cost of sensing systems. This study looks at the most recent wireless and smartphone-supported chemical sensors. The review is divided into four different topics that emphasize the basic types of wireless smartphone-operated chemical sensors. According to a study of 114 original research publications published during recent years, market opportunities for wireless and smartphone-supported chemical sensor systems include environmental monitoring, healthcare and medicine, food quality, sport, and fitness. The issues and illustrations for each of the primary chemical sensors relevant to many application areas are covered. In terms of performance, the advancement of technologies related to chemical sensors will result in smaller and more lightweight, cost-effective, versatile, and durable devices. Given the limitations, we suggest that wireless and smartphone-supported chemical sensor systems play a significant role in the sensor Internet of Things.
... Capillary electrophoresis (CE) has been developed as an alternative separation method for PSTs [36][37][38][39][40][41][42][43][44] as it provides rapid and efficient separation with minimal consumption of sample and reagents. Significantly, it is inherently more miniaturizable than HPLC and a number of portable capillary and microchip electrophoresis devices have been developed [45][46][47][48][49][50][51][52][53][54][55][56], including the Mars Organic Analyser [45,51,53], hand-held portable isotachophoresis (ITP) system [49] and the Medimate Multireader ® [50,56]. CE methods developed for the analysis of PSTs used either UV [36,[40][41][42][43][44] or/and MS [36,39,40,44] detection. ...
... In turn, this could be attributed to a combination of limited funding opportunities to support such engineeringoriented endeavors, a gap in interest and/or preparation of classic chemistry students in the area of electronic circuits and software, and the cost of traditional platforms such as LabView (National Instruments, http://www.ni.com/ labview/). LabView is a solid tool to control systems in a rather commonly known environment and has been extensively used to control analytical instrumentation [19,20]. However, its cost and the need for specific training limit its application in low-resource and educational settings. ...
Understanding basic concepts of electronics and computer programming allows researchers to get the most out of the equipment found in their laboratories. Although a number of platforms have been specifically designed for the general public and are supported by a vast array of on-line tutorials, this subject is not normally included in university chemistry curricula. Aiming to provide the basic concepts of hardware and software, this article is focused on the design and use of a simple module to control a series of PDMS-based valves. The module is based on a low-cost microprocessor (Teensy) and open-source software (Arduino). The microvalves were fabricated using thin sheets of PDMS and patterned using CO2 laser engraving, providing a simple and efficient way to fabricate devices without the traditional photolithographic process or facilities. Synchronization of valve control enabled the development of two simple devices to perform injection (1.6 ± 0.4 μL / stroke) and mixing of different solutions. Furthermore, a practical demonstration of the utility of this system for microscale chemical sample handling and analysis was achieved performing an on-chip acid-base titration, followed by conductivity detection with an open-source low-cost detection system. Overall, the system provided a very reproducible (98%) platform to perform fluid delivery at the microfluidic scale.This article is protected by copyright. All rights reserved
... This is because in the floating injection mode the influence of injection time on sample plug is not significant. In case of other injection mode, such as gate injection mode [20], our investigation revealed that the increased length of the water plug has minor effect on EOF monitoring. Therefore, the injection time of 8 or 10 s with floating injection mode was chosen in our experiments. ...
Electroosmotic flow (EOF) is essential for separation in conventional and microchip electrophoresis as well as liquid manipulation in microfluidic systems. Herein we explored the possibility of applying pure water for EOF measuring in microchip electrophoresis. The principle is that a water plug could greatly decrease the total conductivity of the solution in the microchannel because of its very high electric resistance. In this case, the separation current would be decreased. After the water plug move out of the separation channel, the separation current would be recovered. Thus EOF might be monitored based on the analysis of the current curve. Our experimental results revealed that this approach could reliably and repeatedly monitor EOF in native PDMS microchannel under various conditions. Moreover, EOF in native and gold nanoparticle modified PDMS microchannels could be differentiated. Because the introduction of pure water does not create any contamination or change the channel conditions, this approach could potentially become a routine step for EOF monitoring in microfluidic systems.
... Instrumentation for capillary electrophoresis and microchip capillary electrophoresis has developed greatly in the last decade [118]. Advances include the fabrication of portable units, some of them for general applications and other for specific targets [119][120][121][122]. Regarding extraterrestrial studies, the first portable instrument is the single-channel Mars Organic Analyzer (MOA, Fig. 7) that was developed by Skelley et al. [106] in 2005. ...
The search for signs of life on extraterrestrial planetary bodies is among NASA's top priorities in Solar System exploration. The associated pursuit of organics and biomolecules as evidence of past or present life demands in situ investigations of planetary bodies for which sample return missions are neither practical nor affordable. These in situ studies require instrumentation capable of sensitive chemical analyses of complex mixtures including a broad range of organic molecules. Instrumentation must also be capable of autonomous operation aboard a robotically controlled vehicle that collects data and transmits it back to Earth. Microchip capillary electrophoresis (μCE) coupled to laser-induced fluorescence (LIF) detection provides this required sensitivity and targets a wide range of relevant organics while offering low mass, volume, and power requirements. Thus, this technology would be ideally suited for in situ studies of astrobiology targets, such as Mars, Europa, Enceladus, and Titan. In this review, we introduce the characteristics of these planetary bodies that make them compelling destinations for extraterrestrial astrobiological studies, and the principal groups of organics of interest associated with each. And although the technology we describe here was first developed specifically for proposed studies of Mars, by summarizing its evolution over the past decade, we demonstrate how μCE-LIF instrumentation has become an ideal candidate for missions of exploration to all of these nearby worlds in our Solar System.
... Collaborations with other faculty members have enabled the application of microchips to the analysis of chemical warfare agents [15], the development of the first lab-on-a-robot (Integrated Microchip -Capillary Electrophoresis, Power Supply, Electrochemical Detector, Wireless Unit, and Mobile Platform) [16] and the multivariate evaluation of the separation conditions for five bisphenols [17]. ...
Recent developments in materials, surface modifications, separation schemes, detection systems and associated instrumentation have allowed significant advances in the performance of lab-on-a-chip devices. These devices, also referred to as micro total analysis systems (µTAS), offer great versatility, high throughput, short analysis time, low cost and, more importantly, performance that is comparable to standard bench-top instrumentation. To date, µTAS have demonstrated advantages in a significant number of fields including biochemical, pharmaceutical, military and environmental. Perhaps most importantly, µTAS represent excellent platforms to introduce students to microfabrication and nanotechnology, bridging chemistry with other fields, such as engineering and biology, enabling the integration of various skills and curricular concepts. Considering the advantages of the technology and the potential impact to society, our research program aims to address the need for simpler, more affordable, faster and portable devices to measure biologically active compounds. Specifically, the program is focused on the development and characterization of a series of novel strategies towards the realization of integrated microanalytical devices. One key aspect of our research projects is that the developed analytical strategies must be compatible with each other; therefore, enabling their use in integrated devices. The program combines spectroscopy, surface chemistry, capillary electrophoresis, electrochemical detection and nanomaterials. This article discusses some of the most recent results obtained in two main areas of emphasis: capillary electrophoresis, microchip-capillary electrophoresis, electrochemical detection and interaction of proteins with nanomaterials.
... In the last years several programming languages have been used in mobile devices. One of this is LabVIEW ® , which is a revolutionary system of graphical programming used for applications that includes acquisition, control analysis and data presentation (Berg et al., 2008;Lajara and Pelegrí, 2007). This software is being used in engineer applications because of its great versatility and simplicity of use. ...
... Conditions: 5 mmol·L −1 phosphate buffer (pH=12.0), 1 mmol·L −1 sodium dodecyl sulfate, separation potential 1200 V, t inj =7s, pulsed amperometric detection. Adapted from reference [229]. Tungsten lamp (left) and SMD resistor (right) used to produce thermal markers. ...
Over the last years, there has been an explosion in the number of developments and applications of CE and microchip-CE. In part, this growth has been the direct consequence of recent developments in instrumentation associated with CE. This review, which is focused on the contributions published in the last 5 years, is intended to complement the articles presented in this special issue dedicated to instrumentation and to provide an overview of the general trends and some of the most remarkable developments published in the areas of high-voltage power supplies, detectors, auxiliary components, and compact systems. It also includes a few examples of alternative uses of and modifications to traditional CE instruments.
... CE performed in microfluidic platforms (microchips) represents a powerful analytical tool because it offers several advantages such as short analysis time, efficient separation, minimal reagent consumption, small dimensions and reduced cost of the instrumentation. Moreover, this separation technique can profit by the possibility of integrating essential parts such as high voltage connectors, electrodes and detectors onto the microfluidic support [1,2]. ...
A simple hydrodynamic injection method is proposed here for microchip CE coupled to electrochemical detection. It is based on the use of a precise syringe pump to push the sample into the microfluidic circuit, accompanied by the application of a secondary electric field to the injection channel, soon after the end of the injection step. In such a way, any counter pressure effect taking place when the sample plug enters the micrometric channel is prevented. Suitable optimization of this secondary electric field enables pushing of sample excess to be avoided and a narrow sample plug during the separation step to be maintained. Best conditions for hydrodynamic injection were achieved injecting catechol as model analyte by pressure with a syringe pump set at a flow rate of 8 microL/min for 6 s and applying to the injection channel a secondary high voltage of 700 V soon after the injection was completed. The reliability of this injection procedure has been proved by comparing electropherograms found for samples containing either catechol alone or catechol and dopamine together with those recorded under the same conditions by electrokinetic injection. Repeatability, expressed as RSD and estimated for seven replicate injections, turned out to be 2.1% for peak height of catechol used as single analyte and 0.9 and 1.1% for catechol and dopamine respectively, simultaneously injected.
We report here the first fully automated capillary electrophoresis (CE) system that can be operated underwater. The system performs sample acquisition and analysis by coupling CE to contactless conductivity detection. Using 5 M acetic acid as the background electrolyte (BGE), inorganic cations and amino acids at concentrations as low as 5.2 μM can be separated and identified. This technology could be augmented to include a variety of other detection modes. This system serves as an early prototype for potential future underwater explorers on ocean worlds of the outer solar system such as Europa or Enceladus. This work documents the first step in the development of this general-purpose technology platform.
Capillary electrophoresis (CE) holds great promise as an in situ analytical technique for a variety of applications. However, typical instrumentation operates with open reservoirs (e.g., vials) to accommodate reagents and samples, which is problematic for automated instruments designed for space or underwater applications that may be operated in various orientations. Microgravity conditions add an additional challenge due to the unpredictable position of the headspace (air layer above the liquid) in any two-phase reservoir. One potential solution for these applications is to use a headspace-free, flow-through reservoir design that is sealed and connected to the necessary reagents and samples. Here we demonstrate a flow-through HV reservoir for capillary electrophoresis that is compatible with automated in situ exploration needs, and which can be electrically isolated from its source fluidics (in order to prevent unwanted leakage current). We also demonstrate how the overall system can be rationally designed based on the operational parameters for CE to prevent electrolysis products produced at the electrode from entering the capillary and interfering with the CE separation. A reservoir was demonstrated with a 19 mm long, 1.8 mm inner diameter channel connecting the separation capillary and the HV electrode. Tests of these reservoirs integrated into a CE system show reproducible CE system operation with a variety of background electrolytes at voltages up to 25 kV. Rotation of the reservoirs, and the system, showed that their performance was independent of the direction of the gravity vector. This article is protected by copyright. All rights reserved.
In capillary electrophoresis (CE), analyte identification is primarily based on migration time, which is a function of the analyte's electrophoretic mobility and the electro-osmotic flow (EOF). The migration time can be impacted by the presence of parasitic flow from changes in temperature or pressure during the run. Presented here is a high-voltage-compatible flow sensor capable of monitoring the volumetric flow inside the capillary during a separation with nL/min resolution. The direct measurement of both flow and time allows for compensation of flow instabilities. By expressing the electropherogram in terms of signal versus electromigration velocity instead of time, it is possible to improve the run-to-run reproducibility up to 25×.
There are a variety of complementary observations that could be used in the search for life in extraterrestrial settings. At the molecular scale, patterns in the distributions of organics could provide powerful evidence of a biotic component. In order to observe these molecular biosignatures during spaceflight missions, it is necessary to perform separation science in situ. Microchip electrophoresis is ideally suited for this task. Although this technique is readily miniaturized and numerous instruments have been developed over the last three decades, to date, all lack the automation capabilities needed for future missions of exploration. We have developed a portable, automated, battery-powered, and remotely operated microchip electrophoresis instrument coupled to laser-induced fluorescence detection. This system contains all the necessary hardware and software interfaces for end-to-end functionality. Here, we report the first application of the system for amino acid analysis coupled to an extraction unit in order to demonstrate automated sample-to-data operation. The system was remotely operated aboard a rover during a simulated Mars mission in the Atacama Desert, Chile. This is the first demonstration of a fully automated microchip electrophoresis analysis of soil samples relevant to planetary exploration. This validation is a critical milestone in the advancement of this technology for future implementation on a spaceflight mission.
Undergraduate level fluid mechanics course is traditionally taught as a math-intensive course with the content remaining fairly similar for decades. The course content is usually challenging for students with significant amount of theory and numerous new concepts introduced. In a fluid mechanics course, only a limited amount of state-of-the-art technologies and real-life applications can be included, given the limited time and the material that should be covered. Information on market and career opportunities are often not mentioned in fluid mechanics and other similar courses, which might also be very helpful for undergraduate students. In this paper, we present our efforts and outcomes of introducing the microfluidics module to the undergraduate fluid mechanics course - Fluid Systems - in the Mechanical Engineering Department at University of South Florida, Tampa, FL. Our main aim was to introduce the microfluidics world, give the students an insight to state-of-the-art fluid mechanics applications and micro-technology, and show them the concepts they were taught in the class are applicable to start-of-the-art applications, which could possibly lead to further interest in fluid mechanics. Microfluidics, as the name implies, is the science of fluid mechanics in the micro scale. Micro scale fluid systems are composed of several micro-components capable of processing and precisely manipulating very small volumes (pico-liter to micro-liter range) of fluids. It is an interdisciplinary field involving engineering, bioscience, chemistry, micro-technology and life sciences. The microfluidics module was based on one and half hour-long lecture piggybacked with illustrations and videos. The concept of microfluidics and related theory; its advantages, related challenges; cutting edge applications; market information and career opportunities on microfluidics were introduced. Additionally, an acoustic microfluidic device for particle separation and mixing developed by our research group was also demonstrated and discussed in detail. The evaluation of the module for content, effectiveness and impact was done with the help of a survey composed of nineteen multiple choice questions, student comments and face-to-face discussions. It was observed from students' responses and the survey that the module has drawn significant interest on fluid mechanics and microfluidics. It also inspired a significant number of students to work or conduct research on microfluidics and related areas. The students, in general, were more than happy to see how the concepts they were taught in the class are applicable to microfluidics.
NASA's Solar System exploration goals, particularly in the growing field of astrobiology, involve investigations of a variety of planetary bodies for which sample return missions are neither practical nor affordable (e.g., Europa, Titan, etc.). For these targets, in situ analyses are the only feasible option, and are ideally addressed by in situ instruments capable of wet-chemical analyses of complex mixtures on planets, moons, and primitive bodies. Instrumentation of this kind must be capable of autonomous function aboard a robotically controlled vehicle that collects data and relays it back to Earth. Due to the low power, mass, and volume requirements and extreme sensitivity enabled by lab-on-a-chip analyses, microcapillary electrophoresis is uniquely suited to meet these analytical needs. Although this technology can be adapted for a variety of different Solar System targets (including Titan, Europa, Enceladus, etc.), the bulk of development efforts to date have focused on the Mars Organic Analyzer (MOA), a portable microchip capillary electrophoresis instrument developed for ultrasensitive biomolecular analysis on Mars. MOA technology utilizes a multiwafer stack configuration containing microfluidic valving for fluidic manipulation prior to electrophoresis with ultrasensitive (sub parts per trillion) laser-induced fluorescence detection. In this chapter, we outline the state-of-the-art in this area, and also investigate future directions and applications of microfluidic technology in planetary exploration.
The detection in high-performance liquid chromatography (HPLC) systems devoted to food analysis is usually carried out using spectrophotometric UV–visible (UV–vis) or mass spectrometry (MS) detectors. This chapter deals with the design and integration of electrochemical detectors, namely the amperometric, coulometric, and voltammetric ones, within the HPLC separation system and their compatibility and compromise with the chromatographic conditions necessary to achieve optimum resolution of the analytes in food and agricultural analysis. Liquid mercury has always been a common electrode material, especially in the form of the dropping mercury electrode, used in HPLC-ED for monitoring electrochemical reduction because of its extended negative potential window. In the chapter, a list of selected applications developed in the late years regarding ED in HPLC for the analysis of food products is reported and commented. HPLC-ED is well accepted in the analysis of carbohydrate and natural polyphenols in beverages and food commodities.
The aim of our study was to equip a remote-controlled robotic platform (ORPHEUS-HOPE) with electrochemical system for fast detection of heavy metal ions in water. The platform contains two cameras-one pan/tilt color camera with both manual and automatic parameter settings, and one rigid high resolution color camera for precise vision and zooms to screen printed electrodes at the end of the manipulator. The maximum payload at the end of the manipulator is 0.85 kg. Screen printed electrodes consist with working electrode (WE), reference electrode (RE) and auxiliary electrode (AE).WE electrode (carbon paste) was designed to be as large as possible (in this case geometrically comparable with the diameter of the 3 mm glassy carbon electrode with working area of 7.1 mm2), RE (Ag/AgCl paste) 1.3 mm2 and AE (platinum paste) 6.2 mm2. The analytical parameters of differential pulse voltammetry for remote heavy metals detection (conditional time, step potential, deposition time and temperature) were optimized in this work. Application of robotic platform ORPHEUS-HOPE allowed us to analyze water samples spiked with heavy metal ions in linear ranges as follows:0.8-50 μg.mL-1 in case of Pb(II), 0.04-13 μg.mL-1 in case of Cu(II), 0.2-50 μg.mL-1 Zn(II) and 0.02-25 μg.mL-1 Cd(II). ORPHEUS-HOPE might be helpful for in situ analyzes in environment, possessing conditions incompatible with human presence, such as these after environmental catastrophes.
This chapter highlights the instrumental aspects related to electrochemical detection (ECD) methods applied in food analysis. It highlights representative examples of the instruments and approaches recently presented. All ECD methods are based on the measurement of electronic data produced in a single step from a group of electrodes. Voltammetry comprises a series of electroanalytical techniques in which information about the analyte is collected by measuring the current as a function of the potential applied to the working electrode. The chapter discusses the instrumentation for potentiometric and conductometric techniques. In addition to the bench-top instruments, different companies have also commercially available portable/handheld and battery-or USB-powered potentiostats, which are lightweight, relatively inexpensive, and used-friendly. These portable systems are particularly useful for on-site assessments of food quality and safety. The chapter also describes remotely controlled instruments and electrochemical detectors coupled to microchip capillary electrophoresis.
Capillary zone electrophoresis, the most common form of capillary electrophoresis, was first demonstrated by Jorengson and Lukacs in 1981. Initially, it was coupled with optical forms of detection, as there was no need to disturb the electric field across the capillary. However, optical detection methods depend critically on the size of the detection cell, or in the case of on-capillary detection, the diameter of the capillary itself, which severely hinders the limits of detection achievable with these methods. Electrochemical detection is not subject to the same size dependencies, and is a driving force behind the development of electrochemical detectors for CE application. Conductivity measurements are the only methods that are directly affected by cell size, while amperometry depends only on the size of the working electrode, and potentiometric detection is independent of cell dimensions. However, electrochemical detection in capillary electrophoresis is not an obvious choice, due to the typical detection current being many orders of magnitude higher than the separation current and the potential problems associated with electrode fouling. Due to the advantages associated with EC, however, (selectivity and sensitivity), numerous techniques have been developed to overcome these challenges. As a result, detection limits for most electroactive compounds are in the nanomolar range.
Concern about the environment is increasing and so is the search for analytical methods that make continuous monitoring possible. Microfluidic devices such as lab-on-a-chip emerge as an alternative to the laboratory-based conventional techniques, making possible the development of unmanned monitoring tools. This review covers the last five years on the application of autonomous microfluidic devices for continuous environmental monitoring and addresses the existing demands in this field.
In this paper we demonstrate the proof-of-concept of an optofluidic module capable of simultaneous laser-induced fluorescence (LIF) and absorbance (ABS) detection based on total internal reflection (TIR) optics. We discuss the design of the optofluidic detection module, its fabrication, and the setup used for the proof-of-concept. The injection of sample under test is done using two 3D printed syringe pumps, managing accurate injection and repeatable sample propagation through the detector module. We discuss the process of development behind these pumps and review their technical specifications. With this demonstrator setup we find that the limits of detection for the ABS and LIF detection of coumarin 480 are 500 nM and 100 nM respectively.
In-channel amperometric detection combined with dual-channel microchip electrophoresis is evaluated using a two-electrode isolated potentiostat for reverse polarity separations. The device consists of two separate channels with the working and reference electrodes placed at identical positions relative to the end of the channel, enabling noise subtraction. In previous reports of this configuration, normal polarity and a three-electrode detection system were used for the separations. In the two-electrode detection system described here, the electrode in the reference channel acts as both the counter and reference. The effect of electrode placement in the channels on noise and detector response was investigated using nitrite, tyrosine, and hydrogen peroxide as model compounds. The effects of electrode material and size and type of reference electrode on noise and the potential shift of hydrodynamic voltammograms for the model compounds were determined. In addition, the performance of two- and three-electrode configurations using Pt and Ag/AgCl reference electrodes was compared. Although the signal was attenuated with the Pt reference, the noise was also significantly reduced. It was found that lower LOD were obtained for all three compounds with the dual-channel configuration compared to single-channel, in-channel detection. The dual-channel method was then used for the detection of nitrite in microdialysis samples from sheep.This article is protected by copyright. All rights reserved
This chapter describes the most important features of capillary electrophoretic equipment. A presentation of the important developments in high voltage power supplies for chip CE is followed by preparation of fused silica capillaries for use in CE. Detection systems that are used in capillary electrophoresis are widely described. Here, UV-Vis absorbance measurements are discussed including different types of detection cells—also those less popular (u-shaped, Z-shaped, mirror-coated). Fluorescence detection and laser-induced fluorescence detection are the most sensitive detection systems. Several LIF setups, such as collinear, orthogonal, confocal, and sheath-flow cuvette, are presented from the point of view of the sensitivity they can provide. Several electrochemical detectors for CE, such as conductivity, amperometric, and potentiometric, are also shown and their constructions discussed. CE-MS and much less known CE (CEC)-NMR systems are also described. The examples of automation and robotized CE systems together with their potential fields of application are also presented.
We report the design of a digital system to wirelessly control microchip capillary electrophoresis (CE) equipment and a mobile
unit for chemical analysis. The digital system consists of an embedded processor designed for digital control, decoding and
applying of wirelessly-transmitted test parameters, data acquisition, and mobility control. The design is implemented on a
field programmable gate array (FPGA) and its development board interfaces with four digital-to-analog converters on a newly-designed
3-channel high voltage power supply, electrochemical detector, wireless modems for communications with a base unit, mobile
platform motor controllers, GPS sensor, and an air micropump. The FPGA allows for all the interfacing hardware to perform
CE and transmission of the data acquired from the interfacing electrochemical detector. The work described herein extends
the utilization of microchip capillary electrophoresis to include remotely controlled field applications.
1 Abstract The behavior of liquids at a microscopic scale is quite distinct from that for fluids at a macroscopic level. At
Capillary electrophoresis (CE) and microchip capillary electrophoresis (MCE) are powerful analytical techniques used to analyze chemical and biological samples. For both techniques sample injection and separation are two crucial steps that depend on a reliable high-voltage power supply (HVPS) to ensure reproducible separations. Therefore, the source of high voltage (HV) is considered to be the heart for these instruments. Separation of the analytes occurs due to the influence of an applied potential difference between electrodes placed at the ends of the capillary or channel. As a consequence, the components present in the plug of injection are driven toward the detector. This book chapter is a comprehensive source of information of HVPS for CE and MCE. This chapter covers topics as such as fundamentals of HV, electroosmotic flow control, construction of bipolar HVPS from unipolar HVPS, commercially available HVPS and DC/DC converters, alternative sources of HV, HVPS controllers for MCE, and strategies to measure HV. The chapter also includes practical and safety considerations that can be helpful for development of new CE and MCE instrumentation.
This paper describes a long-range remotely controlled CE system built on an all-terrain vehicle. A four-stroke engine and a set of 12-V batteries were used to provide power to a series of subsystems that include drivers, communication, computers, and a capillary electrophoresis module. This dedicated instrument allows air sampling using a polypropylene porous tube, coupled to a flow system that transports the sample to the inlet of a fused-silica capillary. A hybrid approach was used for the construction of the analytical subsystem combining a conventional fused-silica capillary (used for separation) and a laser machined microfluidic block, made of PMMA. A solid-state cooling approach was also integrated in the CE module to enable controlling the temperature and therefore increasing the useful range of the robot. Although ultimately intended for detection of chemical warfare agents, the proposed system was used to analyze a series of volatile organic acids. As such, the system allowed the separation and detection of formic, acetic, and propionic acids with signal-to-noise ratios of 414, 150, and 115, respectively, after sampling by only 30 s and performing an electrokinetic injection during 2.0 s at 1.0 kV.
Electromigrative techniques such as capillary and microchip electrophoresis (CE and MCE) are inherently associated with various electrochemical phenomena. The electrolytic processes occurring in the buffer reservoirs have to be considered for a proper design of miniaturized electrophoretic systems and a suitable selection of buffer composition. In addition, the control of the electroosmotic flow plays a crucial role for the optimization of CE/MCE separations. Electroanalytical methods have significant importance in the field of detection in conjunction with CE/MCE. At present, amperometric detection and contactless conductivity detection are the predominating electrochemical detection methods for CE/MCE. This paper reviews the most recent trends in the field of electrochemical detection coupled to CE/MCE. The emphasis is on methodical developments and new applications that have been published over the past five years. A rather new way for the implementation of electrochemical methods into CE systems is the concept of electrochemically assisted injection which involves the electrochemical conversions of analytes during the injection step. This approach is particularly attractive in hyphenation to mass spectrometry (MS) as it widens the range of CE-MS applications. An overview of recent developments of electrochemically assisted injection coupled to CE is presented.
Over the past years, the development of capillary electrophoresis (CE) and microchip electrophoresis (ME) systems has grown due to instrumental simplicity and wide application. In both CE and ME, the application of a high voltage (HV) is a crucial step in the electrokinetic (EK) injection and separation processes. Particularly on ME devices, EK injection is often performed with three different modes: gated, pinched, and unpinched. In all these cases, different potential values may be applied to one or multiple channels to control the injection of small sample volumes as well as the separation process. For this reason, the construction of reliable HV power supplies (HVPS) is required. This review covers the advances of the development of commercial and laboratory-built HVPS for CE and ME. Moreover, it intends to be a guide for new developers of electrophoresis instrumentation.
Despite multiple orbiter and landed missions to extraterrestrial bodies in the solar system, including Mars and Titan, we still know relatively little about the detailed chemical composition and quantity of organics and biomolecules in those bodies. For chemical analysis on astrobiologically relevant targets such as Mars, Europa, Titan, and Enceladus, instrumentation should be extremely sensitive and capable of analyzing a broad range of organic molecules. Microchip capillary electrophoresis (μCE) with laser-induced fluorescence (LIF) detection provides this required sensitivity and targets a wide range of relevant markers but, to date, has lacked the necessary degree of automation for spaceflight applications. Here we describe a fully integrated microfluidic device capable of performing automated end-to-end analyses of amino acids by μCE with LIF detection. The device integrates an array of pneumatically actuated valves and pumps for autonomous fluidic routing with an electrophoretic channel. Operation of the device, including manipulation of liquids for sample pretreatment and electrophoretic analysis, was performed exclusively via computer control. The device was validated by mixing of laboratory standards and labeling of amino acids with Pacific Blue succinimidyl ester followed by electrophoretic analysis. To our knowledge, this is the first demonstration of completely automated end-to-end μCE analyses on a single, fully integrated microfluidic device.
The electroanalytical techniques of amperometry, conductometry and potentiometry match well with the instrumental simplicity of CE. Indeed, all three detection approaches have been reported for electrophoretic separations. However, the characteristics of the three methods are quite distinct and these are not related to the optical methods more commonly employed. A detailed discussion of the underlying principles of each is given. The issue of possible effects of the separation voltage on the electrochemical detection techniques is considered in depth, and approaches to the elimination of such interferences are also discussed for each case.
Micro-total analysis systems (microTAS) integrate different analytical operations like sample preparation, separation and detection into a single microfabricated device. With the outstanding advantages of low cost, satisfactory analytical efficiency and flexibility in design, highly integrated and miniaturized devices from the concept of microTAS have gained widespread applications, especially in biochemical assays. Electrochemistry is shown to be quite compatible with microanalytical systems for biochemical assays, because of its attractive merits such as simplicity, rapidity, high sensitivity, reduced power consumption, and sample/reagent economy. This review presents recent developments in the integration of electrochemistry in microdevices for biochemical assays. Ingenious microelectrode design and fabrication methods, and versatility of electrochemical techniques are involved. Practical applications of such integrated microsystem in biochemical assays are focused on in situ analysis, point-of-care testing and portable devices. Electrochemical techniques are apparently suited to microsystems, since easy microfabrication of electrochemical elements and a high degree of integration with multi-analytical functions can be achieved at low cost. Such integrated microsystems will play an increasingly important role for analysis of small volume biochemical samples. Work is in progress toward new microdevice design and applications.
Thiols play a fundamental role in cell biology, biochemistry and pharmacology. Altered thiol levels in body fluids are linked to specific pathological conditions. Glutathione is the most abundant intracellular low-molecular-mass thiol, playing an essential role in protecting cells from toxic species; other relevant thiol-containing compounds are homocysteine (Hcy), cysteine (Cys), cysteinylglycine (CysGly). Plasma aminothiols can be bound to proteins but they also occur free in the disulfide (symmetrical and mixed) and in the reduced forms. The simultaneous determination of these aminothiols, their precursor and metabolites is a useful tool in studying oxidative stress, metabolic and redox regulation. Many capillary electrophoresis methods have been proposed for this purpose, the aim of the present review is to support researchers in the choice of suitable methods for the determination of thiols in body fluids evaluating the different approaches and technologies proposed from the literature.
Numerical modelling technology and software is now being used to underwrite the design of many microelectronic and microsystems components. The demands for greater capability of these analysis tools are increasing dramatically, as the user community is faced with the challenge of producing reliable products in ever shorter lead times.
In this paper we present a platform for evolving spiking neural networks on FPGAs. Embedded intelligent applications require both high performance, so as to exhibit real-time behavior, and flexibility, to cope with the adaptivity requirements. While hardware solutions offer performance, and software solutions offer flexibility, reconfigurable computing arises between these two types of solutions providing a trade-off between flexibility and performance. Our platform is described as a combination of three parts: a hardware substrate, a computing engine, and an adaptation mechanism. We present, also, results about the performance and synthesis of the neural network implementation on an FPGA.
A dc 6 GHz single-pole double-throw (SPDT) switching circuit that employs lateral metal-contact micromachined switches is investigated. The lateral metal-contact switch consists of a set of quasi-finite ground coplanar waveguide (FGCPW) transmission lines and a high-aspect-ratio cantilever beam. A single-pole single-throw (SPST) lateral micromachined switch has an insertion loss of 0.08 dB and a return loss of 32 dB at 5 GHz. The isolation is 32 dB at 5 GHz. The measured insertion loss of the SPDT switching circuit is below 0.75 dB, whereas the return loss is higher than 19 dB at 5 GHz. The isolation at 5 GHz is 33 dB. Pull-in voltage of the switch is 23.3 V and switching time is 35 μs. The size of the SPDT switching circuit is 1.2 mm × 1.5 mm. A main advantage of this circuit structure is simple fabrication process with high yield (>90%) based on the deep reactive ion etching (DRIE) technique of silicon-on-insulator (SOI) wafer and shadow mask technology.
Based on the merits of well-established capillary gas chromatography (GC), metallomesogenic polymer was used as the stationary phase and flame ionization detector (FID) was used as the detector, the analysis of phenolic compounds explored the possibility of application in complex matrices. We proposed the method combined supercritical-fluid extraction (SFE) of phenolic compounds, which had been enriched on the solid supports of XAD-4 resins, and then with their determinations by capillary GC-FID. The SFE parameters suitable for 15 phenols simultaneously adsorbed onto XAD-4 resins in aqueous solution were assessed by a 45 factorial design method. The best results were 5 min static time, 10 min dynamic time, 0.25 ml methanol spiked, 80 °C oven temperature and 410 atm CO2 pressure. Also, other parametric conditions for specific phenols were revealed and analyzed. In the comparison with Soxhlet extraction with regard to the recoveries and reproducibility, the developed SFE was quite superior and helped to reduce the detection limit of aqueous samples to 10−2-fold. Eventually, the polluted soils near a pharmaceutical factory were primarily tested and given the probable distribution.
A novel microchip capillary electrophoresis system with electrochemical detection, using the replaceable microelectrode, is first reported. This kind of electrode can be fabricated in general laboratories and can be replaced quickly with electrodes of different materials according to the requirements of experiments. The end-column electrochemical detection on microchip CE was achieved by fixing the working electrode (such as carbon fiber, Pt, or Au, etc.) through a guide tube on the end of the separation channel. The experiment results indicate that the alignment of the electrode with the channel outlet can be carried out accurately and reproducibly, and therefore, the detection device has low noise and good reproducibility. The detection limit of dopamine is 2.4 x 10(-7) M, which is the lowest result reported so far. The separation and detection of dopamine, 5-hydroxytryptamine and epinephrine using carbon fiber and Pt microdisk electrodes within 50 s was successfully performed.
The interest in microfluidic devices has increased considerably over the past decade due to the numerous advantages of working within a miniature, microfabricated format. This review focuses on recent advances in coupling amperometric detection with microchip capillary electrophoresis (CE). Advances in electrochemical cell design, isolation of the detector from the separation field, and integration of both pre- and postseparation reaction chambers are discussed. The use of microchip CE with amperometric detection for enzyme/immunoassays, clinical and environmental assays, and the determination of neurotransmitters is described.
A currently emerging approach enables more widespread monitoring of health parameters in disease prevention and biomarker monitoring. Miniaturisation provides the means for the production of small, fast and easy-to-operate devices for reduced-cost healthcare testing at the point-of-care (POC) or even for household use. A critical overview is given on the present state and requirements of POC testing, on microTAS elements suited for implementation in future microTAS devices for POC testing and microTAS systems for the determination of clinical parameters.
Microchip capillary electrophoresis emerged in the early 1990s as an interesting and novel approach to the high-speed separation of biological compounds, including DNA and proteins. Since the early development in this area, growth in the research field has exploded and now includes chemists and engineers focused on developing new and better microchips, as well as biologists and biochemists who have begun to apply this exciting and still relatively new methodology to real-world problems. This chapter seeks to outline the historical development of microchip, the key elements of microchip capillary electrophoresis, and finally some of the important applications being developed that utilize microchip capillary electrophoresis.
This review gives an overview of developments in the field of microchip analysis for clinical diagnostic and forensic applications. The approach chosen to review the literature is different from that in most microchip reviews to date, in that the information is presented in terms of analytes tested rather than microchip method. Analyte categories for which examples are presented include (i) drugs (quality control, seizures) and explosives residues, (ii) drugs and endogenous small molecules and ions in biofluids, (iii) proteins and peptides, and (iv) analysis of nucleic acids and oligonucleotides. Few cases of microchip analysis of physiological samples or other “real‐world” matrices were found. However, many of the examples presented have potential application for these samples, especially with ongoing parallel developments involving integration of sample pretreatment onto chips and the use of fluid propulsion mechanisms other than electrokinetic pumping.
Microfabricated fluidic devices have generated considerable interest over the past ten years due to the fact that sample preparation, injection, separation, derivatization, and detection can be integrated into one miniaturized device. This review reports progress in the development of microfabricated analytical systems based on microchip capillary electrophoresis (CE) with electrochemical (EC) detection. Electrochemical detection has several advantages for use with microchip electrophoresis systems, for example, ease of miniaturization, sensitivity, and selectivity. In this review, the basic components necessary for microchip CEEC are described, including several examples of different detector configurations. Lastly, details of the application of this technique to the determination of catechols and phenols, amino acids, peptides, carbohydrates, nitroaromatics, polymerase chain reaction (PCR) products, organophosphates, and hydrazines are described.
This review gives an overview of developments in the field of microchip analysis for clinical diagnostic and forensic applications. The approach chosen to review the literature is different from that in most microchip reviews to date, in that the information is presented in terms of analytes tested rather than microchip method. Analyte categories for which examples are presented include (i) drugs (quality control, seizures) and explosives residues, (ii) drugs and endogenous small molecules and ions in biofluids, (iii) proteins and peptides, and (iv) analysis of nucleic acids and oligonucleotides. Few cases of microchip analysis of physiological samples or other “real-world” matrices were found. However, many of the examples presented have potential application for these samples, especially with ongoing parallel developments involving integration of sample pretreatment onto chips and the use of fluid propulsion mechanisms other than electrokinetic pumping.
Portable instrumentation has become of increasing interest in analytical chemistry, because on-site analysis has various advantages. In this report we describe the construction of a field-portable capillary electrophoresis instrument with potentiometric detection. The apparatus is contained in a PVC case of 340 × 175 × 175 mm size and a total weight of 7.5 kg and can therefore be carried easily by one person. Two lead–acid batteries provide the power for a high voltage module capable of supplying up to 30 kV, and for the detection amplifier electronics. As detectors, miniature coated-wire ion-selective electrodes are used and a precise electrode alignment is achieved by a simple electrode holder cell without the need for a microscope. Data acquisition is carried out by a small analog-to-digital converter board, which is integrated into the unit, and a palmtop personal computer. The instrument was tested on the banks of the river Rhine. As examples, alkali and alkaline earth metal cations and inorganic monovalent anions were analysed in the river water.
There is increasing pressure on industry and regulatory bodies to monitor the discharge of trace metals into the aquatic environment. The determination of trace metals can be achieved to parts per billion (ppb) levels using anodic stripping voltammetry (ASV) at screen printed electrodes, controlled using an NMRC potentiostat coupled with software control. The disposable testheads consist of inexpensive materials and allow for low-cost production in batch processes. Voltammetric (the measurement of current as a function of potential) methods of analysis are attractive for the determination of copper, cadmium, lead and zinc. A three electrode set-up is used both in the preparation of the mercury film on a carbon electrode and in the subsequent anodic stripping voltammetric detection step. The performances of the reference electrodes, the screen-printed carbon and the FPGA based unit have been investigated in this paper.
The addition of surfactants to the separation electrolyte is one of the most convenient ways to modify the electro‐osmotic flow (μEOF) in capillary electrophoresis. However, surfactants spontaneously adsorb to most surfaces; therefore, their presence in the running electrolyte may also affect the electrochemical detection. Changes in selectivity and sensitivity due to dynamic coating of electrode surfaces have been systematically reported during the last 30 years. In this review, some pertinent papers related to the use of surfactants to perform dynamic coatings of the capillary surface are discussed. The proposed mechanisms to explain the enhancements produced by surfactants at the detection step are also discussed along with some specific applications. A particular emphasis was placed on recent reports from our group dealing with the effects of anionic surfactants on the separation and detection of phenolic compounds.
The applicability of a poly(dimethylsiloxane) (PDMS) microfluidic device with contactless conductivity detection for the determination of organophosphonate nerve agent degradation products is reported. Five alkyl methylphosphonic acids, isopropyl methylphosphonic acid (IMPA), pinacolyl methylphosphonic acid (PMPA), O‐ethyl‐N,N‐dimethyl phosphoramidate (EDPA), ethyl methylphosphonic acid (EMPA), and methylphosphonic acid (MPA), (degradation products of Sarin, Soman, Tuban and VX nerve agents) were analyzed by microchip capillary electrophoresis. Experimental conditions for the separation and detection processes have been optimized to yield well‐defined separation and high sensitivity. Under optimal conditions, analyses were completed in less than 2 min. Linear relations between concentration and peak heights were obtained with detection limits in the 1.3–4.5 mg/l range and precision values for the peak heights were in the range of 3.4–6.1% RSD. Applicability of this method for natural (lake and tap) water samples was also demonstrated. Compared to conventional analytical methods, this miniaturized system offers promise for on‐site monitoring of degradation products of chemical warfare agents, with advantages of cost effective construction, simple operation, portability, and minimum sample consumption.
Miniaturized, battery-powered, high-voltage power supply, electrochemical (EC) detection, and interface circuits designed for microchip capillary electrophoresis (CE) are described. The dual source CE power supply provides +/- 1 kVDC at 380 microA and can operate continuously for 15 h without recharging. The amperometric EC detection circuit provides electrode potentials of +/-2 VDC and gains of 1, 10, and 100 nA/V. The CE power supply power is connected to the microchip through an interface circuit consisting of two miniature relays, diodes, and resistors. The microchip has equal length buffer and separation channels. This geometry allows the microchip to be controlled from only two reservoirs using fixed dc sources while providing a consistent and stable sample injection volume. The interface circuit also maintains the detection reservoir at ground potential and allows channel currents to be measured likewise. Data are recorded, and the circuits are controlled by a National Instruments signal interface card and software installed in a notebook computer. The combined size (4 in. x 6 in. x 1 in.) and weight (0.35 kg) of the circuits make them ideal for lab-on-a-chip applications. The circuits were tested electrically, by performing separations of dopamine and catechol EC and by laser-induced fluorescence visualization.
A simple and rapid method has been developed for the analysis of four nonsteroidal anti-inflammatory drugs (NSAIDs) in serum using microchip capillary electrophoresis with pulsed amperometric detection. The selected NSAIDs (salicylic acid, acetaminophen, diflunisal, and diclofenac) are among the most commonly used drugs to treat fever, inflammation, and pain. Used above the therapeutic levels, these drugs can cause a wide variety of adverse effects and their fast analysis could have a significant impact in treatment and recovery of the patients. Several conditions, including separation potential, pH, and concentration of the electrolyte solution were studied to optimize the separation and detection. In this study, salicylic acid, acetaminophen, diflunisal, and diclofenac were separated in less than 2 minutes using a 5 mM borate buffer at pH 11.5 and a separation potential of +1200 V. Linear relationships were obtained between the concentration and peak current in the 0.5–15.3 μg/mL range and detection limits around 0.26 μg/mL. After 30 consecutive injections, the stability of both the response and migration time of the analytes showed relative related deviations of less than 4.6% and 1.0%, respectively. The potential of this method was verified by spiking a bovine serum sample with the four NSAIDs and analyzing the recovery ratio.
There is a need to develop analytical methods that are capable of rapidly measuring small biological markers in the field of metabolomics. Among others, carbohydrates play an important role biologically yet are traditionally hard to detect since they have no chromophore or fluorophore. In the present report, the first application of integrated pulsed amperometric detection (iPAD) coupled with microchip electrophoresis to the analysis of glucose, mannose, sucrose, maltose, glucosamine, lactose, maltotriose and galactose is demonstrated. iPAD is an electrochemical detection mode that can be used for direct detection of carbohydrates, amines and sulfur containing compounds. The effect of different solution parameters, including the buffer concentration, pH and the concentration of SDS on both separation and detection response was analyzed. In addition, a comparison study between PAD and iPAD was performed using glucose, glucosamine, sucrose and maltose as model carbohydrates.
Pulsed electrochemical detection (PED) is an excellent method for detection of analytes that normally foul electrodes. In PED, the detection electrode is first cleaned at a high positive potential, then reactivated at a negative potential dissolving the surface oxide, and finally used to oxidize the analyte at a moderate positive potential. Due to the advantages and versatility of PED, many different variations of the detection waveform can be found in literature. This review focuses on application of PED to CE and in particular, the most commonly used modes: pulsed amperometric detection (PAD) and integrated pulsed amperometric detection (iPAD).
Electrochemistry detection offers considerable promise for capillary-electrophoresis (CE) microchips, with features that include remarkable sensitivity, portability, independence of optical path length or sample turbidity, low cost and power requirements, and high compatibility with modern micromachining technologies. This article highlights key strategies in controlled-potential electrochemical detectors for CE microchip systems, along with recent advances and directions. Subjects covered include the design of the electrochemical detection system, its requirements and operational principles, common electrode materials, isolation from the separation voltage, derivatization reactions, typical applications, and future prospects. It is expected that electrochemical detection will become a powerful tool for CE microchip systems and will lead to the creation of truly portable (and possibly disposable) devices.
Microfabricated fluidic devices have generated considerable interest over the past ten years due to the fact that sample preparation, injection, separation, derivatization, and detection can be integrated into one miniaturized device. This review reports progress in the development of microfabricated analytical systems based on microchip capillary electrophoresis (CE) with electrochemical (EC) detection. Electrochemical detection has several advantages for use with microchip electrophoresis systems, for example, ease of miniaturization, sensitivity, and selectivity. In this review, the basic components necessary for microchip CEEC are described, including several examples of different detector configurations. Lastly, details of the application of this technique to the determination of catechols and phenols, amino acids, peptides, carbohydrates, nitroaromatics, polymerase chain reaction (PCR) products, organophosphates, and hydrazines are described.
This paper reports a simple procedure for coating fused-silica capillaries with poly(diallyldimethyl ammonium chloride) and montmorillonite. The coated capillaries were characterized by performing EOF measurements as a function of buffer pH, number of layers of coating, and number of runs (stability). The coated capillaries showed a highly stable μEOF (run-to-run RSD less than 1.5%, n = 20), allowing continuous use for several days without conditioning. The coated capillaries were then used for the effective separation of nine environmentally important phenolic compounds showing a significant improvement in the resolution, when compared to bare fused-silica capillaries. The EOF of the coated capillaries was constant in alkaline solutions (pH ≥ 7), allowing the optimization of the separation conditions of phenolic compounds without significantly affecting the μEOF.
The prototype of a field-portable battery-powered capillary electrophoresis instrument described here includes a high voltage supply capable of delivering the standard 30 kV at both polarities. The instrument has dimensions of 340 mm×175 mm×175 mm (w×h×d) and a weight of 7.5 kg. Data acquisition is carried out with a portable laptop or palmtop computer. Electrochemical detection was chosen as the straightforward signal transduction methods are relatively easily implemented. For robustness, the amperometric and potentiometric detection modes are carried out in a fixed wall-jet cell without decoupler. Both methods rely on the electrophoretic ground electrode as reference and counter electrode. For conductometric detection the only recently reported contactless version was implemented. The availability of the three complementary electrochemical detection methods allows for great versatility, which includes the ability to determine inorganic cations and anions as well as many organic species of interest.
A simple and fast method for the simultaneous determination of the antioxidants propyl gallate (PG), octyl gallate (OG), lauryl gallate (LG), and nordihydroguaiaretic acid (NDGA) has been established by using microchip micellar electrokinetic chromatography with pulsed amperometric detection. Under the optimum conditions (30 mM borate buffer, pH 9.7, 30 mM sodium dodecyl sulfate, separation voltage of 1200 V and 5 s injection time) the analytes were baseline separated. Linear relationships were found between the concentration and peak current for all the selected antioxidants. The measured detection limits (S/N ≥ 3) of PG, OG, LG, and NDGA were 2.2, 1.4, 2.3, and 4.6 μM, respectively, which corresponds to 2–6 fmol of analyte. This approach has remarkable advantages with respect to other methodologies involving separations and electrochemical detection including minimal sample consumption, higher analysis speed, lower cost, and portability. Additionally, a highly reproducible signal (migration time and peak current) was obtained for a series of injections (n = 30). In order to demonstrate the capabilities of the method, the determination of antioxidants in a commercial food sample is also presented.
The present report describes a new analysis strategy for microchip capillary electrophoresis with pulsed amperometric detection and its application to the determination of glucose. The addition of sodium dodecyl sulfate (SDS) to the mobile phase and detection reservoir stabilized flow rates and enhanced the detection signal for glucose. A higher pH (compared to the running buffer) was used at the waste reservoir in order to improve the detection performance while maintaining good separations. To our knowledge, this is the first report describing the use of post-column pH modification using microchip electrophoresis. Under optimum conditions, a linear relationship between the peak current and the concentration of glucose was found between 10−2–10−5 M, with a limit-of-detection of 1.2 μM. In addition, the separation of glucosamine and glucose was performed at pH 7.1 while the detection was performed at pH 11 to demonstrate the ability to use post-column pH modification.
Capillary electrophoresis (CE) has become a very important micro-analytical method in many fields, such as biology, biomedicine, and environmental and food sciences. However, the small injection volume makes it a challenge to achieve high-sensitivity detection. CE and microchip capillary electrophoresis (MCE) coupled with chemiluminescence (CL) detection have certain advantages from combining the high separation efficiency of CE with the high sensitivity of CL. To date, CE-CL and MCE-CL systems have been used successfully for separating metal ions, amino acids, biomarkers, and bio-macromolecules, such as proteins, enzymes and DNA fragments. In this article, we give an overview on the methodological aspects of CL detection with CE and MCE systems, summarize key applications, and discuss future prospects.
In this paper, we report a miniaturized low-power wireless remote environmental monitoring system. This system has been developed for on-site monitoring of water pollution by heavy-metal ions. The system is composed of three parts: an electrochemical sensor module using microfabricated electrodes for detecting heavy-metal contamination in sample water; a custom potentiostat module including readout circuitry, analog-to-digital converter and microcontroller; and a radio frequency (RF) module for sending detected signals to a base station through wireless communication. The electrochemical sensor module is implemented using microfabricated mercury working electrodes (WEs), solid-state reference electrode (SSRE), and platinum counter electrode (CE). For the low-power operation, direct frequency-shift keying (FSK) modulation and simple binary FSK demodulation methods are used for RF module which is realized using 0.18 μm CMOS technology. All the modules are hybrid integrated in a printed circuit board (PCB) and low-power consumption below 1 mW has been achieved.
The interest in microchip capillary electrophoresis (μ-CE) with electrochemical detection (ECD) has increased considerably because ECD offers perfect features for μ-CE, including remarkable sensitivity, inherent miniaturization and portability, low cost, low-power requirements and great compatibility with microfabrication technologies. This review focuses on recent advances in integrating ECD, especially amperometric detection, with μ-CE. We discuss in detail effects of the separation electric field and development of strategies for isolating and not isolating detection from the separation electric field. We expect that μ-CE-ECD will become a powerful tool for clinical diagnostics, environmental monitoring and biological assays.
The development of a poly(dimethylsiloxane)-based (PDMS-based) microchip electrophoresis system employing dual-electrode electrochemical detection is described. This is the first report of dual-electrode electrochemical detection in a microchip format and of electrochemical detection on chips fabricated from PDMS. The device described in this paper consists of a top layer of PDMS containing the separation and injection channels and a bottom glass layer onto which gold detection electrodes have been deposited. The two layers form a tight reversible seal, eliminating the need for high-temperature bonding, which can be detrimental to electrode stability. The channels can also be temporarily removed for cleaning, significantly extending the lifetime of the chip. The performance of the chip was evaluated using catechol as a test compound. The response was linear from 10 to 500 microM with an LOD (S/N = 3) of 4 microM and a sensitivity of 45.9 pA/microM. Collection efficiencies for catechol ranged from 28.7 to 25.9% at field strengths between 200 and 400 V/cm. Dual-electrode detection in the series configuration was shown to be useful for the selective monitoring of species undergoing chemically reversible redox reactions and for peak identification in the electropherogram of an unresolved mixture.
A thermally pyrolyzed poly(dimethylsiloxane) (PDMS) coating intended to prevent surface adsorption during capillary electrophoretic (CE) [Science 222 (1983) 266] separation of proteins, and to provide a substrate for surfactant adsorption for electroosmotic mobility control was prepared and evaluated. Coating fused-silica capillaries or glass microchip CE devices with a 1% solution of 100 cSt silicone oil in CH2Cl2, followed by forced N2 drying and thermal curing at 400 degrees C for 30 min produced a cross-linked PDMS layer. Addition of 0.01 to 0.02% Brij 35 to a 0.020 M phosphate buffer gave separations of lysozyme, cytochrome c, RNase, and fluorescein-labeled goat anti-human IgG Fab fragment. Respective plates/m typically obtained at 20 kV (740 V cm(-1)) were 2, 1.5, 1.25, and 9.4-10(5). In 50 mM ionic strength phosphate, 0.01% Brij 35 running buffer, the electroosmotic flow observed was about 25% of that in a bare capillary, and showed no pH dependence between pH 6.3-8.2. Addition of sodium dodecylsulfate (SDS) or cetyltrimethylammonium bromide (CTAB) to this running buffer allowed ready control of electroosmotic mobility, mu(eo). Concentrations of SDS between 0.005 to 0.1% resulted in mu(eo) ranging from 3 to 5 x 10(-4) cm2 V(-1) s(-1). Addition of 1 to 2.3 x 10(-4)% (2.7-6.3 microM) CTAB caused flow reversal. CTAB concentrations between 3.5 x 10(-4) and 0.05% (0.0014-1.37 mM) allowed control of mu(eo) between -1 x 10(-4) and -5.0 x 10(-4) cm2 V(-1) s(-1). For both surfactants the added presence of 0.01% Brij 35 provided slowly varying changes in mu(eo) with charged surfactant concentration.
This review gives an overview of developments in the field of microchip analysis for clinical diagnostic and forensic applications. The approach chosen to review the literature is different from that in most microchip reviews to date, in that the information is presented in terms of analytes tested rather than microchip method. Analyte categories for which examples are presented include (i) drugs (quality control, seizures) and explosives residues, (ii) drugs and endogenous small molecules and ions in biofluids, (iii) proteins and peptides, and (iv) analysis of nucleic acids and oligonucleotides. Few cases of microchip analysis of physiological samples or other "real-world" matrices were found. However, many of the examples presented have potential application for these samples, especially with ongoing parallel developments involving integration of sample pretreatment onto chips and the use of fluid propulsion mechanisms other than electrokinetic pumping.
A microfabricated electrophoresis chip with an integrated contactless conductivity detection system is described. The new contactless conductivity microchip detector is based on placing two planar sensing aluminum film electrodes on the outer side of a poly(methyl methacrylate) (PMMA) microchip (without contacting the solution) and measuring the impedance of the solution in the separation channel. The contactless route obviates problems (e.g., fouling, unwanted reactions) associated with the electrode-solution contact, offers isolation of the detection system from high separation fields, does not compromise the separation efficiency, and greatly simplifies the detector fabrication. Relevant experimental variables, such as the frequency and amplitude of the applied ac voltage or the separation voltage, were examined and optimized. The detector performance was illustrated by the separation of potassium, sodium, barium, and lithium cations and the chloride, sulfate, fluoride, acetate, and phosphate anions. The response was linear (over the 20 microM-7 mM range) and reproducible (RSD = 3.4-4.9%; n = 10), with detection limits of 2.8 and 6.4 microM (for potassium and chloride, respectively). The advantages associated with the contactless conductivity detection, along with the low cost of the integrated PMMA chip/detection system, should enhance the power and scope of microfluidic analytical devices.
The separation and detection of underivatized carbohydrates, amino acids, and sulfur-containing antibiotics in an electrophoretic microchip with pulsed amperometric detection (PAD) is described. This report also describes the development of a new chip configuration for microchip electrophoresis with PAD. The configuration consists of a layer of poly(dimethylsiloxane) that contains the microfluidic channels, reservoirs, and a gold microwire, sealed to a second layer of poly(dimethylsiloxane). Example separations of carbohydrates, amino acids, and sulfur-containing antibiotics are shown. The effect of the separation and injection potentials, buffer pH and composition, injection time, and PAD parameters were studied in an effort to optimize separations and detection. Detection limits ranging from 6 fmol (5 microM) for penicillin and ampicillin to 455 fmol (350 microM) for histidine were obtained.
The features of analytical systems utilizing microfluidic devices, especially detection methods, are described. Electrochemical detection (EC), laser-induced fluorescence (LIF), mass spectrometry (MS), and chemical luminescence (CL) methods are covered. EC enables detection without labeling and has been used in recent years because of its low cost and sensitivity. LIF is the most generally used detection method in microchip separations. Use of LED as an excitation source for fluorescence measurement was also developed for the purpose of miniaturization of the entire system, including detection and separation. Although MS enables highly sensitive analysis, the interface between MS and micro channels is still under examination. This review with fifty-two references introduces interesting detection methods for microchip separations. Related separation methods using microfluidic devices are also discussed.
Creatinine, creatine, and uric acid are three important compounds that are measured in a variety of clinical assays, most notably for renal function. Traditional clinical assays for these compounds have focused on the use of enzymes or chemical reactions. Electrophoretic microchips have the potential to integrate separation power of capillary electrophoresis with devices that are small, portable, and have the speed of conventional sensors. The development of a microchip CE system for the direct detection of creatinine, creatine, and uric acid is presented. The device uses pulsed amperometric detection (PAD) to detect the nitrogen-containing compounds as well as the easily oxidizable uric acid. Baseline separation of creatinine, creatine and uric acid was achieved using 30 mM borate buffer (pH = 9.4) in less than 200 s. Linear calibration curves were obtained with limits of detection of 80 microM, 250 microM and 270 microM for creatinine, creatine and uric acid respectively. An optimization of the separation conditions and a comparison of PAD with other amperometric detection modes is also shown. Finally, analysis of a real urine sample is presented with validation of creatinine concentrations using a clinical assay kit based on the Jaffé reaction.
Significant progress in the development of miniaturized microfluidic systems has occurred since their inception over a decade ago. This is primarily due to the numerous advantages of microchip analysis, including the ability to analyze minute samples, speed of analysis, reduced cost and waste, and portability. This review focuses on recent developments in integrating electrochemical (EC) detection with microchip capillary electrophoresis (CE). These detection modes include amperometry, conductimetry, and potentiometry. EC detection is ideal for use with microchip CE systems because it can be easily miniaturized with no diminution in analytical performance. Advances in microchip format, electrode material and design, decoupling of the detector from the separation field, and integration of sample preparation, separation, and detection on-chip are discussed. Microchip CEEC applications for enzyme/immunoassays, clinical and environmental assays, as well as the detection of neurotransmitters are also described.
In the present report, the use of negatively charged surfactants as modifiers of the background electrolyte is reported using poly(dimethylsiloxane) (PDMS) microchips. In particular, the use of anionic surfactants, such as sodium dodecyl sulfate, phosphatidic acid, and deoxycholate, was studied. When surfactants were present in the run buffer, an increase in the electroosmotic flow (EOF) was observed. Two additional effects were also observed: (i) stabilization of the run-to-run EOF, (ii) an improvement in the electrochemical response for several biomolecules. In order to characterize the analysis conditions, the effects of different surfactant, electrolyte, and pH were studied. EOF measurements were performed using either the current monitoring method or by detection of a neutral molecule. The first adsorption/desorption kinetics studies are also reported for different surfactants onto PDMS. The separation of biologically important analytes (glucose, penicillin, phenol, and homovanillic acid) was improved decreasing the analysis time from 200 to 125 s. However, no significant changes in the number of theoretical plates were observed.
Separation and detection of native anhydrous carbohydrates derived from the combustion of biomass using an electrophoretic microchip with pulsed amperometric detection (PAD) is described. Levoglucosan represents the largest single component of the water extractable organics in smoke particles and can be used to trace forest fires or discriminate urban air pollution sources. Detection of levoglucosan and other sugar anhydrides in both source and ambient aerosol samples is typically performed by gas chromatographic (GC) separation with mass spectrometric (MS) detection. This method is cost, time, and labor intensive, typically involving a multistep solvent extraction, chemical derivatization, and finally analysis by GC/MS. However, it provides a rich wealth of chemical information as the result of the combination of a separation method and MS and exhibits good sensitivity. In contrast, microchip capillary electrophoresis offers the possibility of performing simpler, less expensive, and faster analysis. In addition, integrated devices can be fabricated and incorporated with an aerosol collection system to perform semicontinuous, onsite analysis. In the present report, the effect of the separation potential, buffer pH and composition, injection time, and pulsed amperometric detection parameters were studied in an effort to optimize both the separation and detection of anhydrous sugars. Using the optimized conditions, the analysis can be performed in less than a minute, with detection limits ranging from 22 fmol (16.7 microM) for levoglucosan to 336 fmol (258.7 microM) for galactosan. To demonstrate the capabilities of the device, a comparison was made between GC/MS and microchip electrophoresis using an aerosol source sample generated in a wood-burning chamber. A second example utilizing an ambient aerosol sample illustrates a matrix interference necessitating additional method development for application to samples not dominated by wood smoke.
A miniaturized analytical system for separation and detection of three EPA priority phenolic pollutants, based on a poly(dimethylsiloxane)-fabricated capillary electrophoresis microchip and pulsed amperometric detection is described. The approach offers a rapid (less than 2 min), simultaneous measurement of three phenolic pollutants: phenol, 4,6-dinitro-o-cresol and pentachlorophenol. The highly stable response (RSD = 6.1%) observed for repetitive injections (n > 100) reflects the effectiveness of Au working electrode cleaned by pulsed amperometric detection. The effect of solution conditions, separation potential and detection waveform were optimized for both the separation and detection of phenols. Under the optimum conditions (5.0 mM phosphate buffer pH = 12.4, detection potential: 0.7 V, separation potential: 1200 V, injection time: 10 s) the baseline separation of the three selected compounds was achieved. Limits of detection of 2.2 microM (2.8 fmol), 0.9 microM (1.1 fmol), and 1.3 microM (1.6 fmol) were achieved for phenol, 4,6-dinitro-o-cresol and pentachlorophenol, respectively. A local city water sample and two over-the-counter sore-throat medicines were analyzed in order to demonstrate the capabilities of the proposed technique to face real applications.
This paper describes on-chip micellar electrokinetic chromatography (MEKC) separation of bisphenol A and 3 kinds of alkylphenols, which have been recently recognized as endocrine disrupting chemicals for fish by the Japanese government, using microchip capillary electrophoresis with UV detection. We successfully obtained high-speed separation of the phenolic chemicals within 15 s as optimizing in microfluidic controls and MEKC separation conditions. We obtained fairly good linearity with correlation coefficient of over 0.98 from 0 to 50 mg/l phenolic chemicals except for 4-nonylphenol, which sample is the mixture of many geometrical isomers (r = 0.86). The values of the relative standard deviation for peak height in 50 mg/l phenolic chemicals were less than 8% except for bisphenol A (11.0%). The limits of detection obtained at a signal-to-noise ratio of 3 were from 5.6 to 20.0 mg/l. To realize on-site monitoring, we described strategy for on-chip MEKC analysis of the phenolic chemicals in waters using a portable analyzer based on microfluidic devices.
In the present chapter, some basic definitions about the photolithography process are explained and then the standard preparation of the silicon wafer, the fabrication of the mold, and the preparation and assembly of poly(dimethylsiloxane) (PDMS)-based microchips are discussed. The purpose of this chapter is to describe the most used techniques for preparation of PDMS microchips. A list of tips is included in order to provide a troubleshooting guide for the most common difficulties found during the fabrication process. Some recent alternative approaches to microfabrication are also discussed.
A micrototal analytical method assembling in-channel preconcentration, separation, and electrochemical detection steps has been developed for trace phenolic compounds. A micellar electrokinetic chromatography separation technique was coupled with two preconcentration steps of field-amplified sample stacking (FASS) and field-amplified sample injection (FASI). An amperometric detection method with a cellulose-dsDNA-modified, screen-printed carbon electrode was applied to detect preconcentrated and separated species at the end of the channel. The microchip was composed of three parallel channels: first, two are for the sample preconcentration using FASS and FASI methods, and the third one is for the separation and electrochemical detection. The modification of the electrode surface improved the detection performance by enhancing the signal-to-noise characteristic without surface fouling of the electrode. The method was examined for the analysis of eight phenolic compounds. Experimental parameters affecting the analytical performance of the method were assessed and optimized. The preconcentration factor was increased by about 5200-fold as compared with a simple capillary zone electrophoretic analysis using the same channel. Reproducible response was observed during multiple injections of samples with a RSD of <8.0%. The calibration plots were shown to be linear (with the correlation coefficient between 0.9913 and 0.9982) over the range of 0.4-600 nM. The sensitivity was between 0.17 +/- 0.001 and 0.48 +/- 0.006 nA/nM, with the detection limit of approximately 100 to approximately 150 pM based on S/N = 3. The applicability of the method to the direct analysis of trace phenolic compounds in water samples was successfully demonstrated.
In this paper, we describe the separation and detection of six phenolic acids using an electrophoretic microchip with pulsed amperometric detection (PAD). The selected phenolic acids are particularly important because of their biological activity. The analysis of these compounds is typically performed by chromatography or standard CE coupled with a wide variety of detection modes. However, these methods are slow, labor intensive, involve a multistep solvent extraction, require skilled personnel, or use bulky and expensive instrumentation. In contrast, microchip CE offers the possibility of performing simpler, less expensive, and faster analysis. In addition, integrated devices can be custom-fabricated and incorporated with portable computers to perform on-site analysis. In the present report, the effect of the separation potential, buffer pH and composition, injection time and PAD parameters were studied in an effort to optimize both the separation and detection of these phenolic acids. Using the optimized conditions, the analysis can be performed in less than 3 min, with detection limits ranging from 0.73 microM (0.10 microg/mL) for 4-hydroxyphenylacetic acid to 2.12 microM (0.29 microg/mL) for salicylic acid. In order to demonstrate the capabilities of the device, the degradation of a mixture of these acids by two aquatic plants was followed using the optimized conditions.