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Wax screen-printing as a low-cost, simple, and rapid method for fabricating paper-based microfluidic devices (µPADs) is reported here. Solid wax was rubbed through a screen onto paper filters. The printed wax was then melted into the paper to form hydrophobic barriers using only a hot plate. We first studied the relationship between the width of a...
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... colorless areas yield hydrophilic features. The transparency is then used to create the screens at a local screen-printing shop. Solid wax was rubbed through the screen (200 mesh of nylon on an aluminium frame) onto the paper. The printed wax was then melted on a hot plate at 100 C for 60 s, absorbing into the paper to form hydrophobic barriers (Fig. 1). The patterned paper was ready for use after removing the paper from the hot plate and allowing it to cool to room temperature (<10 s). The screen was placed on tissue paper on a hot plate and heated for 60 s to remove the residual ...
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... utility of mPADs fabricated by the wax screen-printing was demonstrated using electrochemical and colorimetric detec- tion for glucose and total iron using the design shown in Fig. S1 †. Electrodes were constructed on paper devices using a previously reported screen-printing method. 5,8 Glucose oxidase (1 mL of 645 U mL À1 solution) was added to the electrode region. Ascorbic acid (0.5 mL of 1 mM solution) and 1,10-phenanthroline (0.5 mL of 0.25 M solution) were spotted in the colorimetric test zone for total iron ...
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... glass, ceramic, paper, and cotton or similar fabrics. The type of ink also depends on the printing surface and the application. Typically, printing materials include liquid inks and dyes. We reported here the use of solid wax as a printing material for screen-printing hydrophobic barriers on paper (wax screen-printing method) as shown in Fig. 1. Wax is environmentally friendly and much cheaper and easier to obtain than photoresist or PDMS. Moreover, our fabrication method is accomplished without the use of a clean room, UV lamp, organic solvents, or sophisticated instrumentation. From previous reports, wax printing needs a wax printer ($$2500 US) but printing screens required ...
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... shown in a previous report that photoresist residues can also interfere with amperometric detection in paper- based microfluidic devices. 7 In order to evaluate the utility of wax screen-printed mPADs, the simultaneous determination of glucose and total iron in control human serum samples was performed. The design of the paper device is shown in Fig. S1 †. Total iron was analyzed by a colorimetric method involving the formation of a red-colored complex between 1,10-phenanthroline and iron(II). The color intensity increased with iron concentration (Fig. 5a). Color intensity calibrations were done using Adobe PhotoshopÔ in gray scale mode using 1200 pixel area in a circle shape within a ...
Citations
... PADs have several advantages that make them a potentially powerful platform. These advantages include low cost, low reagent consumption, excellent chemical compatibility, portability, global accessibility, and ease of storage and transportation (Cate et PADs with colorimetric methods have received considerable attention, since the colorimetric detection mechanism is based on the color change presented by a reaction between the analyte and a chromogenic reagent (Ferreira et Xie et al., 2019), enabling user-friendliness, convenience, low-cost equipment and data acquisition using scanners, smartphones or digital cameras (Dungchai et al., 2011;Martinez et al., 2008). Therefore, we present a paper-based analytical device for simultaneous determination of Hg(II) and Pb(II) in natural waters from the São Francisco River, Brazil. ...
Hg(II) and Pb(II) are considered potentially toxic metals (PTMs) that can be found in several ecosystems, including water systems such as lakes, rivers and groundwaters. These species are classified as human carcinogens and non-biodegradable pollutants, leading to neurological and nutritional disorders, as well as chronic diseases. Due to its relevance, several methods have been developed to determine the concentration of these PTMs; however, they require costly reagents, laborious operation and complex equipment. Herein, we present a simple-to-use and low-cost paper-based device (PAD) for Hg(II) and Pb(II) determination in natural water samples based on the colorimetric reaction between these PMTs and the dithizone colorimetric probe. The color intensity was employed as an analytical signal, through the color channels of the RGB scale. Under optimized conditions, a linear correlation of r = 0.989 and r = 0.991 and linear range of 1–20 µg/mL and 5–30 µg/mL were obtained for Hg(II) and Pb(II), respectively. After analytical optimization, the method was employed for PMTs determination using real samples from São Francisco River, Brazil. Thus, this method proved to be appropriate for Hg(II) and Pb(II) determination in natural water samples and is a easy, low-cost and straightforward alternative for the simultaneous determination of Hg(II) and Pb(II).
... These dPAD sensors enable quantification of the target analytes without the need for software or instrumentation for signal readout, offering ease of use and affordability [23][24][25]. Quantitative analysis is straightforward, involving the measurement of the distance length of a color change along the channel, which can be performed by naked-eye readout [26,27]. Currently, Saengsawang et al. [28] established fluorescent dPADs for E. coli determination using the loop-mediated isothermal amplification (LAMP) assay. ...
The development of distance-based paper analytical devices (dPADs) integrated with molecularly imprinted polymers (MIPs) to monitor Escherichia coli (E. coli) levels in food samples is presented. The fluidic workflow on the device is controlled using a designed hydrophilic bridge valve. Dopamine serves as a monomer for the formation of the E. coli–selective MIP layer on the dPADs. The detection principle relies on the inhibition of the E. coli toward copper (II) (Cu²⁺)-triggered oxidation of o-phenylenediamine (OPD) on the paper substrate. Quantitative detection is simply determined through visual observation of the residual yellow color of the OPD in the detection zone, which is proportional to E. coli concentration. The sensing exhibits a linear range from 25.0 to 1200.0 CFU mL⁻¹ (R² = 0.9992) and a detection limit (LOD) of 25.0 CFU mL⁻¹ for E. coli detection. Additionally, the technique is highly selective with no interference even from the molecules that have shown to react with OPD to form oxidized OPD. The developed device demonstrates accuracy and precision for E. coli quantification in food samples with recovery percentages between 98.3 and 104.7% and the highest relative standard deviation (RSD) of 4.55%. T-test validation shows no significant difference in E. coli concentration measured between our method and a commercial assay. The proposed dPAD sensor has the potential for selective and affordable E. coli determination in food samples without requiring sample preparation. Furthermore, this strategy can be extended to monitor other molecules for which MIP can be developed and integrated into paper-microfluidic platform.
Graphical Abstract
... While these devices are typically substandard in terms of resolution and channel smoothness compared to those created using techniques like photolithography, they are significantly cheaper and use non-toxic reagents [21]. Some examples of wax patterning techniques include: wax dipping [22], wax screen printing [23][24][25][26], and wax printing and casting [27][28][29][30]. Wax dipping is a fabrication technique that uses a laser cutter to create an iron mold, which is then dipped into molten wax. ...
A wax-based contact printing method to create microfluidic devices is demonstrated. This printing technology demonstrates a new pathway to rapid, cost-effective device prototyping, eliminating the use of expensive micromachining equipment and chemicals. Derived from the traditional Ukrainian Easter egg painting technique called “pysanky” a series of microfluidic devices were created. Pysanky is the use of a heated wax stylus, known as a “kistka”, to create micro-sized, intricate designs on the surface of an egg. The proposed technique involves the modification of an x-y-z actuation translation system with a wax extruder tip in junction with Polydimethysiloxane (PDMS) device fabrication techniques. Initial system optimization was performed considering design parameters such as extruder tip size, contact angle, write speed, substrate temperature, and wax temperature. Channels created ranged from 160 to 900 μm wide and 10 to 150 μm high based upon system operating parameters set by the user. To prove the capabilities of this technology, a series of microfluidic mixers were created via the wax technique as well as through traditional photolithography: a spiral mixer, a rainbow mixer, and a linear serial dilutor. A thermo-fluidic computational fluid dynamic (CFD) model was generated as a means of enabling rational tuning, critical to the optimization of systems in both normal and extreme conditions. A comparison between the computational and experimental models yielded a wax height of 57.98 μm and 57.30 μm, respectively, and cross-sectional areas of 11,568 μm2 and 12,951 μm2, respectively, resulting in an error of 1.18% between the heights and 10.76% between the cross-sectional areas. The device’s performance was then compared using both qualitative and quantitative measures, considering factors such as device performance, channel uniformity, repeatability, and resolution.
... 102 Although they had good precision and reproducibility they were costly and complicated under unfurnished laboratory conditions. New techniques such as screen printing, 103 flexographic printing, 104 wax screening/ printing, 105,106 inkjet etching and printing, 107,108 laser treatment, 109 cardiovascular disease 110 and other automated tools 111,112 have been introduced to ease the possibility of commercialisation. The aforementioned methods fabricate µPADs on a single layer. ...
Microfluidic technologies have garnered significant attention due to their ability to rapidly process samples and precisely manipulate fluids in assays, making them an attractive alternative to conventional experimental methods. With the potential for revolutionary capabilities in the future, this concise review provides readers with insights into the fascinating world of microfluidics. It begins by introducing the subject's historical background, allowing readers to familiarize themselves with the basics. The review then delves into the fundamental principles, discussing the underlying phenomena at play. Additionally, it highlights the different aspects of microfluidic device design, classification, and fabrication. Furthermore, the paper explores various applications, the global market, recent advancements, and challenges in the field. Finally, the review presents a positive outlook on trends and draws lessons to support the future flourishing of microfluidic technologies.
... With the advancements in the smartphone industry, smartphone-based colorimetric sensors are emerging as an appropriate and lowcost alternative to complex and huge instruments. Meanwhile, given broad access to smartphones, the opportunity to detect various analytes, including thrombin, in remote and undeveloped areas is provided [23,24]. In smartphone-based colorimetric sensors, the changes corresponding to the target analyte are digitally recorded by their camera. ...
Fibrinogen-modified gold nanoparticles (Fib-AuNPs) and 3,3′,5,5′-tetramethylbenzidine (TMB) substrate besides hydrogen peroxide (H2O2) were applied for assessment of the biomarker thrombin. Fib-AuNPs have catalytic active sites for the oxidation of TMB besides H2O2 and cause the color change of the substrate. Moreover, they can lead to the enhancement in the absorption wavelengths of 650 and 370 nm. By the addition of thrombin to Fib-AuNPs, fibrinogen turns into fibrin, and AuNPs are surrounded by fibrin. Therefore, their active catalytic sites for the oxidation of TMB besides H2O2 are covered by fibrin and cannot cause color change and absorption increase as before. The relationship between the average variations of the color intensity and changes in the absorption wavelengths at 650 and 350 nm with different concentrations of bovine thrombin added to Fib-AuNPs was studied. In such manner, three sensitive colorimetric approaches have been developed for the identification of bovine thrombin with the linear range of 20–120 pM and the limit of detection (LOD) of 17.54 pM for the average color intensity (G + B), the linear range of 20–120 pM and the LOD of 13.41 pM for the absorption peak at 650 nm, and the linear range of 40–140 pM with the LOD of 18.85 pM for absorption peak at 370 nm. The practical application of this biosensing platform was indicated through the successful determination of bovine thrombin in bovine serum. The satisfactory RSD ( < 10%) and recovery values (99.11–107.61%) confirmed the feasibility of the fabricated sensor.
Graphical abstract
... SU-8 photoresist, an epoxy-type near-ultraviolet negative photoresist, can be directly deposited on a paper substrate to form hydrophilic microstructural channels through photolithography [39], inkjet printing, or screen printing [40,41] (Figure 2). However, the production of negative light adhesive SU-8 is intricate and expensive, and its low flexibility contributes to the fragility of the paper chip [42]. To enhance flexibility while maintaining low cost and environmental friendliness, Han et al. substituted SU-8 with a photosensitive material called polyurethane acrylate (PUA) [43]. ...
Food safety and quality are paramount concerns for ensuring the preservation of human life and well-being. As the field of food processing continues to advance, there is a growing interest in the development of fast, instant, cost-effective, and convenient methods for detecting food safety issues. In this context, the utilization of paper-based microfluidic chips has emerged as a promising platform for enabling rapid detection, owing to their compact size, high throughput capabilities, affordability, and low resource consumption, among other advantages. To shed light on this topic, this review article focuses on the functionalization of paper-based microfluidic surfaces and provides an overview of the latest research and applications to colorimetric analysis, fluorescence analysis, surface-enhanced Raman spectroscopy, as well as their integration with paper-based microfluidic platforms for achieving swift and reliable food safety detection. Lastly, the article deliberates on the challenges these analytical methods and presents insights into their future development prospects in facilitating rapid food safety assessment.
... Paper-based microfluidic devices are mostly fabricated by creating patterned hydrophobic barriers in hydrophilic paper, thus limiting fluid flow to within a targeted area. Filling or coating some of the pores among the hydrophilic cellulose fibers in paper using a hydrophobic material, such as wax [6,7], polydimethylsiloxane (PDMS) [8], polystyrene [9], poly(o-nitrobenzyl methacrylate) [10], is a simple way to achieve this goal. Inkjet printing, flexo printing, screen printing, plotting, stamping, chemical vapor deposition, photolithography, and other methods have been used to deposit hydrophobic materials onto paper, creating a designed pattern [5]. ...
Microfluidic devices with a free-standing structure were printed directly on polymer films using the functional materials that form interconnected pores. The printed devices can transport fluids by capillary action in the same fashion as paper-based microfluidic devices, and they can handle much smaller sample volumes than typical paper-based devices. Detection of glucose was performed using both colorimetric and electrochemical methods, and the observed limits of detection (LOD) were similar to those obtained with paper-based microfluidic devices under comparable testing conditions. It is demonstrated that printed microfluidic devices can be fabricated using printing processes that are suitable for high-volume and low-cost production and that the integration of microfluidic channels with electrodes is straightforward with printing. Several materials that are printable and form interconnected pores are presented.
... Paper, which is composed of numerous cellulose layers, is a popular substrate due to its low cost, light weight, microporous structure enabling microfluidics, high abundance, environmental friendliness, and ease of bulk manufacture [39]. Thus, paper has drawn much interest in sensor and device fabrication as it is flexible, portable, disposable, and easy to operate [40][41][42][43][44][45][46]. Proper fabrication of electrochemical paper-based biosensors depends on the selection of paper material, design of 2D and 3D electrodes, formation of a hydrophobic wall to delineate microfluidic spreading area, surface modification of electrodes, and analyte conjugation [47]. ...
Paper-based biosensors are a potential paradigm of sensitivity achieved via microporous spreading/microfluidics, simplicity, and affordability. In this paper, we develop decorated paper with graphene and conductive polymer (herein referred to as graphene conductive polymer paper-based sensor or GCPPS) for sensitive detection of biomolecules. Planetary mixing resulted in uniformly dispersed graphene and conductive polymer ink, which was applied to laser-cut Whatman filter paper substrates. Scanning electron microscopy and Raman spectroscopy showed strong attachment of conductive polymer-functionalized graphene to cellulose fibers. The GCPPS detected dopamine and cytokines, such as tumor necrosis factor-alpha (TNF-α), and interleukin 6 (IL-6) in the ranges of 12.5–400 µM, 0.005–50 ng/mL, and 2 pg/mL–2 µg/mL, respectively, using a minute sample volume of 2 µL. The electrodes showed lower detection limits (LODs) of 3.4 µM, 5.97 pg/mL, and 9.55 pg/mL for dopamine, TNF-α, and IL-6 respectively, which are promising for rapid and easy analysis for biomarkers detection. Additionally, these paper-based biosensors were highly selective (no serpin A1 detection with IL-6 antibody) and were able to detect IL-6 antigen in human serum with high sensitivity and hence, the portable, adaptable, point-of-care, quick, minute sample requirement offered by our fabricated biosensor is advantageous to healthcare applications.
... Similarly, there is the screen-printing method, which uses photolithography to pattern the desired design on a screen ( Figure 2IV). Through the patterned screen, the required pattern is created on paper by pressing hydrophobic wax or ink [40]. The greatest advantage of this method is its low cost, while the biggest drawbacks are using a new screen every time for the fabrication and low resolution. ...
... method, which uses photolithography to pattern the desired design on a screen ( Figure 2IV). Through the patterned screen, the required pattern is created on paper by pressing hydrophobic wax or ink [40]. The greatest advantage of this method is its low cost, while the biggest drawbacks are using a new screen every time for the fabrication and low resolution. ...
Over the past ten years, microfluidic paper-based analytical devices (micro-PADs) have attracted a lot of attention as a viable analytical platform. It is expanding as a result of advances in manufacturing processes and device integration. Conventional microfluidics approaches have some drawbacks, including high costs, lengthy evaluation times, complicated fabrication, and the necessity of experienced employees. Hence, it is extremely important to construct a detection system that is quick, affordable, portable, and efficient. Nowadays, micro-PADs are frequently employed, particularly in electrochemical analyses, to replicate the classic standard laboratory experiments on a miniature paper chip. It has benefits like rapid assessment, small sample consumption, quick reaction, accuracy, and multiplex function. The goal of this review is to examine modern paper microfluidics-based electrochemical sensing devices for the detection of macromolecules, small molecules, and cells in a variety of real samples. The design and fabrication of micro-PADs using conventional and the latest techniques have also been discussed in detail. Lastly, the limitations and potential of these analytical platforms are examined in order to shed light on future research.
... Paper, which is composed of numerous cellulose layers, is a popular substrate due to its low cost, lightweight, high abundance, environmental friendliness, and ease of bulk manufacture (Liang et al., 2019). So, paper has drawn much interest in sensor and device fabrication as it is flexible, portable, disposable, and easy to operate Cate et al., 2015;Dungchai et al., 2009Dungchai et al., , 2011Liang et al., 2020;Mazzeo et al., 2021;Zou et al., 2018). Proper fabrication of electrochemical paper-based biosensors depends on the selection of paper material, design of 2D and 3D electrodes, formation of a hydrophobic wall, surface modification of electrodes, and analyte conjugation (Loo & Pui, 2020). ...
Two-dimensional (2D) nanomaterials have gained popularity over the last few decades due to their excellent mechanical, electrical, and thermal properties. These unique properties of 2D nanomaterials can be exploited in various applications specially in sensor, energy, and separation devices. In this study, the sensing and energy generation performance of PVDF/PAni fiber mat systems is made by the forcespinning method with and without graphene coating. The graphene-coated nanocomposites show an average output voltage of 75 mV (peak-to-peak) which is 300% higher compared to bare fiber mats and an output current of 24 mA (peak-to-peak) by gentle finger pressing. Moreover, the graphene-coated PVDF/PAni was investigated as a promising system for temperature, vibration, and airflow sensing, as well as a water tide energy harvesting piezoelectric nanogenerator. Additionally, a low-cost, single-step, sophisticated graphene-enhanced elastomeric nanocomposite was fabricated for multifunctional sensing and device fabrication by using a shear batch mixer. A direct ink writing of the prepared ink was used for fabricating a membrane on a metal mesh substrate. Furthermore, the study also showed the enhanced battery performance of chemical vapor-deposited pyrolytic carbon coatings on nanoparticles and nanofibers.
