JM Research Lab
Rambhai Barni Ratchabhat University, Thailand
ACADEMIC ARTICLES
User-friendly diameter-based measurement paper sensor for chloride detection in water
Chloride (Cl−) is an anion widely distributed in nature. It is also an essential parameter to consider when assessing the water quality for ensuring drinking water safety, preventing infrastructure damage, mitigating environmental impact, identifying groundwater contamination. This work presents the first development of a diameter-based measurement paper sensor for chloride analysis using the reaction based on a Mohr's precipitation titration. The paper sensor that has a circular shape with 3-cm diameter was pre-coated with AgNO3 and CrO42− forming brown precipitates of the Ag2CrO4. The sensor was sealed using lamination films with 3-mm diameter hole-punched inlets on the top of the lamination film for sample delivery. To detect chloride, the sensor was simply immersed into the sample. The chloride solution flows into the central sample inlet and spreads radially to undergo the displacement reaction with Ag2CrO4 precipitate, forming AgCl white precipitate whose diameter proportional to the chloride that can be observed within 3 min. Concentration of AgNO3 used was found to impact the analytical figures of merit. The lower AgNO3 concentration yields lower limit of detection, narrower linear range but higher sensitivity. The sensor was applied for chloride analysis in tap water, drinking water and industrial water and the chloride concentration obtained from the developed sensors are not significant differences from those obtained from the standard titration method at 95% confidence interval (two tailed P = 0.08) indicating that the developed sensor provides accurate analysis of chloride in water samples from various sources. The developed sensor was used by the untrained staffs for on-site of analysis chloride in tap water collected at 26 locations in SaenSuk Municipality area, Chonburi, Thailand. The results showed that the chloride level in all samples is in range of 52.2–84.7 mg L−1 which is far below the acceptable range set by the Provincial Waterwork Authority of Thailand (< 250 mg L−1) indicating that the tap water used in this area is safe for consumers.
Microfluidic paper-based analytical devices for simultaneous detection of oxidative potential and copper in aerosol samples
The potential reach of point-of-care (POC) diagnostics into daily routines for exposure to reactive oxygen species (ROS) and Cu in aerosolized particulate matter (PM) demands that microfluidic paper-based analytical devices (μPADs) take into consideration the simple detection of these toxic PM components. Here, we propose μPADs with a dual-detection system for simultaneous ROS and Cu(II) detection. For colorimetric ROS detection, the glutathione (GSH) assay with a folding design to delay the reaction yielded complete ROS and GSH oxidation, and improved homogeneity of color development relative to using the lateral flow pattern. For electrochemical Cu(II) determination, 1,10-phenanthroline/Nafion modified graphene screen-printed electrodes showed ability to detect Cu(II) down to pg level being low enough to be applied to PM analysis. No intra- and inter-interference affecting both systems were found. The proposed μPADs obtained LODs for 1,4-naphthoquinone (1,4-NQ), used as the ROS representative, and Cu(II) of 8.3 ng and 3.6 pg, respectively and linear working ranges of 20 to 500 ng for ROS and 1 × 10−2 to 2 × 102 ng for Cu(II). Recovery of the method was between 81.4 and 108.3% for ROS and 80.5–105.3% for Cu(II). Finally, the sensors were utilized for simultaneous ROS and Cu(II) determination in PM samples and the results statistically agreed with those using the conventional methods at 95% confidence.
An electrochemical paper-based analytical sensor for one-step latex protein detection
Exposure to natural rubber latex (NRL) can result in sensitivity to NRL protein with resulting allergic reactions. Low-cost, portable, simple, sensitive analytical tools for NRL protein measurements are needed for rapid and accurate assessments of allergenic risks at the point-of-care (POC) instead of using traditional methods that require large and expensive instruments, long-time analysis, and complex sample preparation steps. Here, an electrochemical paper-based analytical device (ePAD) is presented by combining sample preparation and electrochemical detection within a single device to offer a one-step NRL analysis. The lack of antibodies and/or enzymes against NRL makes POC analysis difficult. In this work, detection is based on electrochemical measurement of the remaining Cu after in situ protein complexation instead of more complex biological assays for the first time. Graphene screen-printed electrodes modified with 1,10-phenanthroline and Nafion were used in the ePAD to improve Cu signal 18-fold relative to unmodified carbon screen-printed electrodes. The optimum parameters including 1,10-phenanthroline concentration, reaction time between Cu and protein, and the starting Cu concentration were 5% w/v, 1 min, and 600 μg mL−1, respectively. In addition to short analysis time (4 min), the system selectivity indicated no other interfering species affecting protein detection. The proposed ePAD achieved an LOD of 3.0 mg dL−1 and a linear range of 10.0–200.0 mg dL−1. Finally, the proposed sensors were applied for NRL protein detection and the results were not significantly different from the traditional Lowry method at 95% confidence.
Simple biodegradable plastic screen-printing for microfluidic paper-based analytical devices
The goal of using microfluidic paper-based analytical devices (μPADs) in remote areas has prompted the development of uncomplicated, affordable, and environmentally-friendly fabrication methods. Here, screen-printed biodegradable polycaprolactone (PCL) as a simple, low-cost, and non-toxic alternative approach to create μPADs was introduced. No need for a heating step contributed to low PCL dispersion resulting in high resolution hydrophobic barriers. The proposed method achieved a narrowest hydrophilic channel and hydrophobic edge of 510 ± 40 μm and 490 ± 30 μm, respectively. The method was used to generate several designs for Cr3+ and Cl− detections. For Cr3+ analysis, silver nanoparticles were used as the colorimetric probe to selectively measure Cr3+ using a spot format that achieved a limit of detection (LOD) of 15.0 μg L-1 and a linear working range of 50.0–1000.0 μg L-1. For Cl- determination, the distance-based pattern using traditional precipitation titration was utilized to resolve the coffee ring effect from colorimetric detection. The method gave an LOD and a linear range for Cl- detection of 10.0 mg L-1 and 10.0–500.0 mg L-1, respectively. Finally, the μPADs were applied for Cl- analysis in instant noodle seasonings and the results significantly agreed with those using the traditional titration at 95 % confidence.
Janus Electrochemical Paper-Based Analytical Devices for Metals Detection in Aerosol Samples
Exposure to trace metals in airborne particulate matter (PM) has been linked to various adverse health effects. Quantifying metals in PM is important; however, current analytical tools tend to be bulky and expensive. A need therefore exists for more rapid, low-cost, portable tools for multiplexed determination of metals in PM. Electrochemical paper-based devices (ePADs) have been used for detecting metals in PM but require different devices and methods for different metals, making the systems more complicated than desired. Recently reported Janus ePADs offer a solution to this problem by allowing for multiple electrochemical experiments from a single sample. Here, we sought to determine if a Janus ePAD containing four independent channels and working electrodes could be used for simultaneous detection of multiple metals in PM. Online sample pretreatment in each channel during sample delivery yielded optimal conditions for each experiment. The design allows the device to conduct square-wave anodic stripping voltammetry (SWASV) and square-wave cathodic stripping voltammetry (SWCSV) for simultaneous detection of Cd, Pb, Cu, Fe, and Ni from a single sample. Two detection zones each with shared reference and counter electrodes were used for SWASV and SWCSV, respectively. The proposed sensors reached LODs down to 0.5, 0.5, 1.0, 0.5, and 1.0 μg L–1, for Cd(II), Pb(II), Cu(II), Fe(II), and Ni(II), respectively. The linear working ranges were 0.5–400.0 μg L–1 for Cd(II), Pb(II), and Fe(II), 1.0–400.0 μg L–1 for Cu(II), and 0.5–200.0 μg L–1 for Ni(II). The devices were applied for Cd(II), Pb(II), Cu(II), Fe(II), and Ni(II) determination in PM samples, and the results agreed with those using traditional ICP-MS analyses at 95% confidence.
AgNP/Bi/Nafion-modified Disposable Electrodes for Sensitive Zn(II), Cd(II), and Pb(II) Detection in Aerosol Samples
A new method for modifying electrodes with Ag nanoparticles (AgNPs) using electrospray deposition for sensitive, selective detection of Zn(II), Cd(II), and Pb(II) in aerosol samples when combined with Bismuth and Nafion coating and square-wave anodic stripping voltammetry (SWASV) is reported. Carbon stencil-printed electrodes (CSPEs) fabricated on a polyethylene transparency (PET) sheet were produced for an inexpensive, simple to fabricate, disposable sensor that can be used with the microliter sample volumes for analysis. Sensor performance was improved by modifying the electrode surface with electrospray-deposited AgNPs. The use of electrospray deposition resulted in more uniform particle dispersion across the electrode surface when compared to drop-casting. Using AgNP-modified electrodes combined with Bi and Nafion, experimental detection limits (LODs) of 5.0, 0.5, and 0.1 μg L−1 for Zn(II), Cd(II), and Pb(II), respectively, were achieved. The linear working ranges were 5.0–400.0 μg L−1, 0.5–400.0 μg L−1, and 0.1–500.0 μg L−1 for Zn(II), Cd(II), and Pb(II), respectively. Interference studies showed Cu(II) was the only metal that interfered with this assay but inference could be eliminated with the addition of ferricyanide directly to the sample solution. This electrochemical sensor was applied for the simultaneous determination of Zn(II), Cd(II), and Pb(II) within source particulate matter (PM) samples collected on filters using an aerosol test chamber.
Low-cost reusable sensor for cobalt and nickel detection in aerosols using adsorptive cathodic square-wave stripping voltammetry
A low-cost electrochemical sensor with Nafion/Bi modification using adsorptive stripping voltammetry for Co and Ni determination in airborne particulate matter and welding fume samples is described. Carbon stencil-printed electrodes (CSPEs) manufactured on low-cost PET films were utilized. Dimethylglyoxime (DMG) was used as a Co(II) and Ni(II) chelator with selective chemical precipitation for trace electrochemical analysis. Electrochemical studies of the Nafion/Bi-modified CSPE indicated a diffusion-controlled redox reaction for Co and Ni measurements. The Nafion coating decreased the background current and enhanced the measured peak current. Repeatability tests based on changes in percent relative standard deviation (RSD) of peak current showed the electrode could be used at least 15 times before the RSD exceeded 15% (the reported value of acceptable repeatability from Association of Official Analytical Chemists (AOAC)) due to deterioration of electrode surface. Limits of detection were 1 μg L− 1 and 5 μg L− 1 for Co and Ni, respectively, which were comparable to electrochemical sensors requiring more complicated modification procedures. The sensor produced a working range of 1–250 and 5–175 μg L− 1 for Co and Ni, respectively. Interference studies showed no other metal species interfered with Co and Ni measurements using the optimized conditions. Finally, the developed sensors were applied for Co and Ni determination in aerosol samples generated from Co rods and a certified welding-fume reference material, respectively. Validation with ICP-MS showed no statistically different results with 95% confidence between sensor and the ICP methods.
Electrophoretic separations on Parafilm-paper-based analytical devices
Microfluidic paper-based analytical devices (mPADs) have gained significant attention in recent years for applications ranging from clinical diagnostics to environmental testing. However, separation on mPADs remains challenging to implement, particularly in complex samples. This has revived interest in revisiting paper chromatography and paper electrophoresis in mPADs to address these needs. Here, laminated Parafilm-paper (l-paper) is applied to fabricate electrophoretic devices. This approach yields a free-standing channel, leading to improved peak resolution relative to previous electrophoretic separations in traditional wax-printed mPADs. Major factors influencing the separation, including Joule heating, electroosmotic flow, and electrophoretic mobility, were investigated. As a result of paper’s high ratio of surface area (78%) to pore volume (22%) resulting in slow heat dissipation, a usable applied field strength range of 0–200 V cm−1 was employed to avoid Joule heating. The electroosmotic flow of the system was found to be 2.5 × 10−5 ± 7.7 × 10−7 cm2 V−1 s−1 and the electrophoretic mobility of chlorophenol red was 1.2 × 10−4 ± 7.7 × 10−7 cm2 V−1 s−1. Basic separation protocols were optimized using colorimetric detection of chlorophenol red and indigo carmine dyes as representative molecules. Paper type, channel width, and applied potential were then used to optimize the separations. Addition of an injection port to the device improved resolution and reduced peak broadening. Finally, the separation of fluorescein isothiocyanate (FITC) and l-glutamic acid (Glu) labeled with FITC, was successfully carried out using the l-paper electrophoretic device. Imaging with a microscope was found to achieve reduced peak broadening and increased resolution relative to imaging with a mobile camera, due to elimination of background signal, achieving a 72 ±â€¯4% conjugation of Glu and FITC.
Improving electrophoretic separations using A parafilm-paper-based analytical platform
This has revived interest in revisiting paper chromatography and paper electrophoresis in mPADs to address these needs. Here, laminated Parafilm-paper (l-paper) is applied to fabricate electrophoretic devices. This approach yields a free-standing channel, leading to improved peak resolution relative to previous electrophoretic separations in traditional wax-printed mPADs. Major factors influencing the separation, including Joule heating, electroosmotic flow, and electrophoretic mobility, were investigated. As a result of paper’s high ratio of surface area (78%) to pore volume (22%) resulting in slow heat dissipation, a usable applied field strength range of 0–200 V cm−1 was employed to avoid Joule heating. The electroosmotic flow of the system was found to be 2.5 × 10−5 ± 7.7 × 10−7 cm2 V−1 s−1 and the electrophoretic mobility of chlorophenol red was 1.2 × 10−4 ± 7.7 × 10−7 cm2 V−1 s−1. Basic separation protocols were optimized using colorimetric detection of chlorophenol red and indigo carmine dyes as representative molecules. Paper type, channel width, and applied potential were then used to optimize the separations. Addition of an injection port to the device improved resolution and reduced peak broadening. Finally, the separation of fluorescein isothiocyanate (FITC) and l-glutamic acid (Glu) labeled with FITC, was successfully carried out using the l-paper electrophoretic device. Imaging with a microscope was found to achieve reduced peak broadening and increased resolution relative to imaging with a mobile camera, due to elimination of background signal, achieving a 72 ±â€¯4% conjugation of Glu and FITC.
Electrochemistry on Paper-based Analytical Devices
Even though they were introduced less than a decade ago, electrochemical paper-based devices (ePADs) have attracted widespread attention because of their inherent advantages in many applications. ePADs combine the advantages of microfluidic paper-based devices (low cost, ease of use, equipment free pumping, etc.) for sample handling and processing with the advantages of sensitive and selective detection provided by electrochemistry. As a result, ePADs provide simplicity, portability, reproducibility, low cost and high selectivity and sensitivity for analytical measurements in a variety of applications ranging from clinical diagnostics to environmental sensing. Herein, recent advances in ePAD development and application are reviewed, focusing on electrode fabrication techniques and examples of applications specially focused on environmental monitoring, biological applications and clinical assays. Finally, a summary and prospective directions for ePAD research are also provided.
Recent Developments in Paper-Based Microfluidic Devices
During this time over 1 000 articles have been published in the field, making a full comprehensive review citing all papers impossible. As a result, we seek to highlight the papers we find to be most impactful for the field. We also limited our search criteria and resulting discussion to papers describing analytical measurements. In recent years, paper as a substrate material has been used more frequently for electronics as evidenced by a number of excellent reviews. While many of these reports have bearing and importance to analytical measurements, they are not discussed here in interest of maintaining focus. The same is true of lateral flow immunoassays. Lateral flow immunoassays warrant a separate review based on their ubiquity and have been covered recently. Finally, searches were done using a combination of Google Scholar, Web of Science, PubMed, and SciFinder. In addition, high impact journals were scanned for manuscripts that did not readily appear with standard search terms. Despite these extensive searches, we have, without a doubt, missed many excellent papers relating to paper microfluidics. For those papers missed, we apologize in advance.
