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... our disposable sensor, the spectrum of the outgoing light ( , ) and thus the response of the sensor R( , ) is determined by two phenomena: the photon diffusion process in the hybrid-material drop applied to the optical fiber tip and the absorption of the indicator. Both these processes are pH-dependent; indeed, the size of the hybrid drop depends on the pH level of the solution and so, varying the pH, different photon optical paths are possible. In order to characterize the sensing probe, measurements were performed at room temperature in standard pH buffers (Fisher Scientific) evaluating the response of the disposable sensor R( , ) . According to the schematic representation in Fig. 5, the sensitive tip of the POF was immersed in 20 ml of sample solution; measurements were taken at 5 min after changing the pH level, monitored with the reference pH meter, which has a measuring uncertainty of 0.05 units. The system response R( , ) was calculated acquiring a reference spectrum ( , ) at pH ref =10 and varying the pH of the solution from 9 to 4. To evaluate the temporal response of the probe to a rapid change in pH, the pH value of the solution has been staircase decreased from 8 to 5 with unitary steps of duration 10 s each. The same protocol has been applied for the reverse direction of the staircase, i.e. from 5 to 8. Also during these measurements the testing solution was continuously monitored with the reference pH meter. The temporal response has been investigated firstly visually inspecting the color changes and then acquiring continuously the spectrum ( , ) and calculating R( , ) as a function of time. The optical properties of the interrogation system have been determined according to the measurement procedures reported in section 4.1. Spectra ( ) , ( ) and their ratio are shown in Fig. 6 together with the emission spectrum of the halogen lamp WLS. Other distortions of the halogen lamp spectrum are due to the transmission properties of the optical components used in the interrogation setup. ( ) Figure 6b shows the ratio that, according to Eq. (5), is proportional to the spectral ( ) response of the interrogation system. The spectral region of interest in our application is 500-600 nm, i.e. green-yellow-red; since the response of the interrogation system is satisfactorily flat in this interval, as shown in Fig. 6b, the information of interest is not corrupted. The spectral properties of the sensing indicator have been measured according to the procedure reported in section 4.2. The absorbance spectra of phenol red at different pH values are shown in Fig. 7; the maximum of all the spectra is well visible at the wavelength of about 560 nm. According to literature (Wang, 2003), at this wavelength the phenol red molecules exhibit a very low absorption that can be significantly enhanced by increasing the pH of the solution. Note that the absorbance at 560 nm showed a sharp transaction when the pH of the solution changed from 5 to 8. As shown in Fig. 8, the point of inflection (sigmoidal fitting function Eq. (6) equal to 0.5) corresponds to the apparent pKa value of 7.9. This value is in good agreement with the pKa of phenol red in aqueous solution reported in literature (Budavari, 1989). The sensor characteristics have been measured according to the procedure reported in section 4.3. As shown in Fig. 9, a visual inspection of the probe at two different pH values of the solution underlines the swelling described in the previous sections. The spectra Δ ( , ) = ( , ) − , acquired at different values of pH are shown in Fig. 10. Observing Fig. 10, it is clear that the swelling/shrinking processes induce a change in the amplitude of the whole spectrum. As far as these phenomena are concerned, parameters A and S were considered to quantify the response of the sensor. In particular, as shown in Fig. 11, given a typical spectrum Δ ( ) , parameter A and S were calculated as follow: (i) the two maxima = ( , ) , = ( , ) and the minimum = ( , ) of Δ ( ) have been calculated using a standard Matlab © routine; (ii) the equation of the line joining M 1 and M 2 has been calculated as ( ) = ( − ) ; (iii) A has been defined as ( ) − and S as ( ) . As shown in Fig. 11, parameter S is correlated to the spectrum amplitude and thus to swelling/shrinking processes while A is strictly related to the absorption (at about λ = 560 nm) performed by the indicator. In Fig. 12, parameters A and S were calculated for each spectrum acquired and the normalized results are plotted against pH. Parameter A exhibits a sharp transaction changing the pH of the solution from 5 to 8. The experimental data was fitted by the Boltzmann (sigmoidal) function according to Eq. (6). The point of inflection (sigmoidal fitting function equal to 0.5) corresponds to the apparent pKa value = 6.8 . This value is lower than the measured value of pKa=7.9 of phenol red in aqueous solution (Fig. 8). However, the pKa value can be shifted to lower pH with increasing ionic strength as observed by Holobar et al. (Holobar, 1993), and this phenomenon could occur also in our hybrid matrix. An increase in the value of pH determines a higher swelling of the hybrid drop, as shown in Fig. 9, which leads to an increase in the distance between the optical fiber tip and the probe- liquid interface and a consequent decrease in the mean optical path of the photons through the probe. As a consequence, according to Eq. (3), also the sensor response diminished. Coherently, as shown in Fig. 12b, parameter S decreased linearly with the pH of the solution. The linear fit of the experimental data exhibits a slope of 0.17. The response time of the probe PEO8000-8:2-PR was measured. A trade-off between the response time and the indicator leaching together with the adhesion between the sensitive matrix and the POF is required. In fact, high molecular weight PEO improves the adhesion and diminishes the indicator leaching, but causes long response time of the sensor. In general there are two different time constant; in fact, when pH is changed from 10 to 3, the sensor was found to reach 90% of the regime signal intensity ( τ 90 ) between 1 and 2 seconds, while changing the pH from a low value to a high one resulted in longer response times that can be quantify in the order of some minutes, i.e. the kinetics depends on the direction of ...
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... change (the 90% of the regime signal intensity was not reached in the time scale of the experiment, i.e. 10 seconds per step). This agrees with other experimental observations reported in literature (Ismail, 2002; Badini, 1995). Empirical quantification of this sensor behavior is shown in Fig. 13. In Fig. 13, the parameter A (blue line) is represented as a function of time together with the value of the reference pH (dashed line). We think that the slow response time observed changing the pH from 5 to 8 is strictly associated with the swelling/shrinking kinetics of the sensitive drop. Finally, the kinetics of swelling/shrinking has shown to be dependent on the direction of the pH change. This complex mechanism meddles in the photons propagation in the sensitive drop and thus in the response of the probe. The mean lifetime of disposable sensors, checked in the continuous mode operation at a pH level in the middle of the range, is two days. The reusability, tested with a series of probes checked once a day at a pH level in the middle of the range and preserved dry, has a mean life of one month. Table 1 shows these and other analytical parameters of the sensor. We present a disposable sensor based on a low-cost plastic optical fiber that covers an important pH range for physiological applications, e.g. in medicine and biotechnology, with excellent sensitivity. Some other advantages of the proposed sensor are: simple realization process, small size, high resistance to aggressive environments and electrical isolation. The sensor characterization has been performed using a simple optical setup based on a single wavelength measurement. Nevertheless according to Lei (Lei, 2010), a ratiometric approach could improve the sensing overall performance. To this purpose, the isosbestic wavelength, i.e. 480 nm, highlighted in the spectra shown in Fig. 7, could be conveniently exploited. 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... The absorbance of phenol red solutions at 560 nm is an indicator of pH, as previously described [73][74][75]. Phenol red is a pH indicator changing color from yellow below pH 6.8 to bright pink above pH 8.2. ...
Bacterial pneumonia is a common infection of the lower respiratory tract that can afflict patients of all ages. Multidrug-resistant strains of Acinetobacter baumannii are increasingly responsible for causing nosocomial pneumonias, thus posing an urgent threat. Alveolar macrophages play a critical role in overcoming respiratory infections caused by this pathogen. Recently, we and others have shown that new clinical isolates of A. baumannii, but not the common lab strain ATCC 19606 (19606), can persist and replicate in macrophages within spacious vacuoles that we called Acinetobacter Containing Vacuoles (ACV). In this work, we demonstrate that the modern A. baumannii clinical isolate 398, but not the lab strain 19606, can infect alveolar macrophages and produce ACVs in vivo in a murine pneumonia model. Both strains initially interact with the alveolar macrophage endocytic pathway, as indicated by EEA1 and LAMP1 markers; however, the fate of these strains diverges at a later stage. While 19606 is eliminated in an autophagy pathway, 398 replicates in ACVs and are not degraded. We show that 398 reverts the natural acidification of the phagosome by secreting large amounts of ammonia, a by-product of amino acid catabolism. We propose that this ability to survive within macrophages may be critical for the persistence of clinical A. baumannii isolates in the lung during a respiratory infection.
... The absorbance of phenol red solutions at 560 nm is an indicator of pH, as previously described (Held, 2018;Paye et al., 2018;Rovati et al., 2012). To analyze the pH changes in A. baumannii cultures during bacterial growth, indicated strains were maintained overnight in LB broth at 37 °C under shaking conditions. ...
Bacterial pneumonia is a common infection of the lower respiratory tract that can afflict patients of all ages. Multidrug-resistant strains of Acinetobacter baumannii are increasingly responsible for causing nosocomial pneumonias, thus posing an urgent threat. Alveolar macrophages play a critical role in overcoming respiratory infections caused by this pathogen. Recently, we and others have shown that new clinical isolates of A. baumannii, but not the common lab strain ATCC 19606 (19606), can persist and replicate in macrophages within spacious vacuoles that we called Acinetobacter Containing Vacuoles (ACV). In this work, we demonstrate that the modern A. baumannii clinical isolate 398, but not the lab strain 19606, can infect alveolar macrophages and produce ACVs in vivo in a murine pneumonia model. Both strains initially interact with the alveolar macrophage endocytic pathway, as indicated by EEA1 and LAMP1 markers; however, the fate of these strains diverges at a later stage. While 19606 is eliminated in an autophagy pathway, 398 replicates in ACVs and are not degraded. We show that 398 reverts the natural acidification of the phagosome by secreting large amounts of ammonia, a by-product of amino acid catabolism. We propose that this ability to survive within macrophages may be critical for the persistence of clinical A. baumannii isolates in the lung during a respiratory infection.
... After 72 h, the pH of the central compartment of each chamber was measured for the pH group and control group. For the leakage group, the absorbance of each compartment was measured using an absorptiometer and the absorbance at a wavelength of 560 nm was recorded [27]. Based on the measured values, the amount of leakage was estimated by dividing the average of the absorbance of the left and right compartments by the absorbance of the central compartment. ...
Three-dimensional (3D) printers mainly create 3D objects by stacking thin layers of material. The effect of the tools created using the fused deposition modeling (FDM) 3D printer on nerve cells remains unclear. In this study, the effects of polytetrafluoroethylene (PTFE) models and two different types of polylactic acid (PLA) models (white or natural), were created using the FDM 3D printer on axon extension were compared using the Campenot chamber. Neurons were isolated from the dorsal root ganglia and added to the central compartment of the Campenot chambers after isolation, processing, and culturing. On day 7, after the initiation of the culture, the difference of the axon extensions to the side compartments of each group was confirmed. We also compared the pH and the amount of leakage when each of these chambers was used. The PLA was associated with a shorter axon extension than the PTFE (white p = 0.0078, natural p = 0.00391). No difference in the pH was observed ( p = 0.347), but there was a significant difference on multiple group comparison ( p = 0.0231) in the amount of leakage of the medium. PTFE was found to be a more suitable material for culturing attachments.
... As the measured liquid, buffer solutions with values 4.0, 5.0, 6.0, 7.0, 8.0, 9.0, and 10.0 were employed in the test. Figure 7a depicts the typical measured absorbance spectra of phenol red at different pH values [53], where two significant peaks appear at wavelengths 430 nm (peak 1) and 560 nm (peak 2). Between the peaks is an isosbestic point at a wavelength of about 470 nm. ...
This paper presents a miniature, all-silica, flow-injection sensor. The sensor consists of an optical fiber-coupled microcell for spectral absorption measurements and a microfluidic reagent injection system. The proposed sensor operates in back reflection mode and, with its compact dimensions, (no more than 200 µm in diameter) enables operation in small spaces and at very low flow rates of analyte and reagent, thus allowing for on-line or in-line colorimetric chemical sensing.
... Then pH measurement based on Thin-Core Fiber Capital Interferometer (TCFMI) optical fiber with coating layer uses Sodium Alginate (SA) and Polythylenimine (PEI) with a pH range that can be measured from 2 to 11 with a sensitivity of 1.51 nm/pH [7]. In addition, the utilization of POF as a pH sensor uses a gel [8]. ...
... In previous studies, it was still using a complicated sensor system, namely optical fiber coated with sol gel as sensing elements and having a small measurement range [8]. In this study, pH sensor will be made using POF with cladding and without cladding types. ...
... It causes a decreasing of output voltage and output power, so the range and sensitivity of sensor are also greater. This research has suitability with previous researches about POF as pH sensor that increasing the pH range results cause higher sensitivity [7,8]. Another suitability of the research is the higher of refractive index of the solution measured using a POF sensor causes the sensor output power decreases [11]. ...
Plastic optical fiber testing as a sensor can be applied in pH measurement using loop configuration. It was made of a plastic optical fiber material with two types of peel, namely with cladding and without cladding. Sensor testing was done by dipping the sensor into buffer solutions with varying pH values. The light intensity from the LED will experience power losses due to the effect of adding the solution refractive index around the sensor, so the phototransistor will receive smaller the light intensity. Changes of light intensity in the optical fiber causes the output voltage read on the microcontroller and the computer decreases. The best measurement was obtained at sensor type of without cladding 4 loops with sensitivity 0.035 V/pH and resolution 0.029 pH. Aplication of plastic optical fiber as sensor for pH measurement has advantages such as low cost, real time, high sensitivity, accurate and simple measurement.
... ANYTYPES of pH sensor are easily available in commercial market like pH strips, indicator reagent and amperometric or potentiometric device are the most commonly used [1]. The earliest chemical indicator of pH measurement is pH strips or litmus paper and is still in use for laboratory activities at school. ...
Optical pH sensors offer a promising alternative method over the existence pH electrochemical sensor and other. Due to ability to achieve high performance, electrical passive operation, simplicity and price effectiveness. Recently, significant research efforts have been devoted to pH sensors for the detection of pH variation in high resolution short range changes. It becomes important to consider ways to heighten the sensitivity of the indicator by improving combination of the material and simple method of sensor fabrication. Effort has been put in studying the fabrication and the sensitivity of film towards pH range in physiological application. Most optical sensors consist of an indicator which is immobilized in a polymer matrix. In this research, polyaniline act as a sol - gel matrix to support pH sensitive indicator molecules which is phenol red. Polyaniline has been found to be versatile functional material which is the most suitable organic material to act as a matrix in aqueous medium and capability to sense on pH changes. The combination between polyaniline with phenol red will enhance the sensitivity of the sensor. The sensing capabilities of the device in term its optical absorption intensity with different pH values were explored. Besides that, simpler and low cost methods was prepared and developed. Through the final investigations, it was found that the phenol red immobilized in a polyaniline film on a portion of fiber optic developed by deposited for 4 layers at thickness is 88.46 nm, withdrawal speed with 15 mm/s and re-cladded length is 15mm/s is the best optimized parameters.
... Thus, immobilization of the indicator on fiber is crucial for the development of optical pH sensor. Sol-gel process is a popular approach to immobilize the indicator dyes [5][6][7][8] in view of its simplicity and versatility. The process key parameters such as reactant formulation, catalyst, water content and reaction temperature can be exploited and adjusted to tailor the physicochemical properties of the film in order to optimize the sensor performances [9][10][11]. ...
... Finally through condensation, silanols react with siloxanes to form porous sol-gel matrices after aging and drying processes under ambient atmospheres. The reaction scheme for such process is depicted in Fig. 1 [5,9,12]. ...
The fabrication and characterization of an optical fiber pH sensor for the detection range 2 – 7 are described. The sensing element was prepared by coating the uncladded middle portion of a multimode plastic clad silica fiber (PCF) with xerogel film of immobilized bromophenol blue (BPB) prepared by a sol-gel process. The exponential decay of the evanescent wave at the core-cladding interface of the multimode fiber was utilized to determine the pH response. The objective of this work is to analyze the measurement of the fiber optic sensing probe towards various pH level. The intensity of the absorbance was analyzed using statistical technique (Statistical Package for the Social Sciences, SPSS) to identify the significant pH range that can be used as a reference in developing the sensor instrumentation in the future. pH2 shows the highest significance among all pH values based on the statistical results using error plots.
... While many detectors have been implemented with silica FBGs [86,87], only a few works have used polymer fibers. Sol-gel coated PMMA fibers and dye doped micro-structured POF leveraging fluorescence have already been reported [88,89]. These configurations based on absorbance can be affected by unwanted intensity fluctuations and temperature changes, issues that can be alleviated using FBGs. ...
Interest in polymer optical fiber Bragg gratings (POFBGs) arises from the different material properties and sensing modalities brought by polymers relative to silica. Polymer fibers typically offer twice the sensitivity to temperature of conventional silica fiber and increased sensitivity to strain overall. In addition, polymer fibers have higher elastic limits and as a result a larger range of operation for physical constraints. While some polymers are effectively humidity insensitive, others present inherent humidity sensitivity. Their organic properties also allow a variety of chemical processes to create (bio)chemical sensors, with the consequences of fiber breakage in situ being less hazardous than silica. These attributes have led to the use of POFBGs for applications that remain complex using silica fibers. This review article covers the progress towards commercialization and the increasing number of specific applications.
... Because some part of the cladding had been replaced by pH-sensitive material (described at section 2.2 and 2.3), partial absorption of the light will be occured when the light touches this material at the given wavelength. Part of the incoming Partially of light is absorbed into the film there because it interacts with the analytic material and the rest of incoming light that is not absorbed will be reflected back towards the core of fiber optic [36]. Due to the interaction of light with the analytic material causes the reflected light intensity is reduced, this optical signal will be guided back to detector. ...
... Curve fitting was performed using the four-parameter sigmoid model on SigmaPlot 12.0 for Windows (Chicago, IL, USA). Phenol red has previously been shown to be the optimal choice of indicator since it is vibrantly yellow at near neutral pH and transitions to bright purple at basic pH values above 8.2 (Rovati et al., 2012;Tram et al., 2014). This translates to a clear contrast between test and control samples that enables rapid visual determination of the presence of target. ...
Ingestion of water containing toxic contaminants above levels deemed safe for human consumption can occur unknowingly since numerous common contaminants in drinking water are colorless and odorless. Uranyl is particularly problematic as it has been found at dangerous levels in sources of drinking water. Detection of this heavy metal-ion species in drinking water currently requires sending a sample to a laboratory where trained personnel use equipment to perform the analysis and turn-around times can be long. A pH-responsive colorimetric biosensor was developed to enable detection of uranyl in water which coupled the uranyl-specific 39E DNAzyme as a recognition element, and an enzyme capable of producing a pH change as the reporter element. The rapid colorimetric assay presented herein can detect uranyl in lake and well water at concentrations relevant for environmental monitoring, as demonstrated by the detection of uranyl at levels below the limits set for drinking water by major regulatory agencies including the World Health Organization (30 μg/L). This simple and inexpensive DNAzyme-based assay enabled equipment-free visual detection of 15 μg/L uranyl, using both solution-based and paper-based pH-dependent visualization strategies.
