Recently, the development of electrochemical biosensors as part of microfluidic devices has garnered a great deal of attention because of the small instrument size and portability afforded by the ...integration of electrochemistry in microfluidic systems. Electrode fabrication, however, has proven to be a major obstacle in the field. Here, an alternative method to create integrated, low cost, robust, patternable carbon paste electrodes (CPEs) for microfluidic devices is presented. The new CPEs are composed of graphite powder and a binder consisting of a mixture of poly(dimethylsiloxane) (PDMS) and mineral oil. The electrodes are made by filling channels molded in previously cross-linked PDMS using a method analogous to screen printing. The optimal binder composition was investigated to obtain electrodes that were physically robust and performed well electrochemically. After studying the basic electrochemistry, the PDMS-oil CPEs were modified with multi-walled carbon nanotubes (MWCNT) and cobalt phthalocyanine (CoPC) for the detection of catecholamines and thiols, respectively, to demonstrate the ease of electrode chemical modification. Significant improvement of analyte signal detection was observed from both types of modified CPEs. A nearly 2-fold improvement in the electrochemical signal for 100 μM dithiothreitol (DTT) was observed when using a CoPC modified electrode (4.0 ± 0.2 nA (n = 3) versus 2.5 ± 0.2 nA (n = 3)). The improvement in signal was even more pronounced when looking at catecholamines, namely dopamine, using MWCNT modified CPEs. In this case, an order of magnitude improvement in limit of detection was observed for dopamine when using the MWCNT modified CPEs (50 nM versus 500 nM). CoPC modified CPEs were successfully used to detect thiols in red blood cell lysate while MWCNT modified CPEs were used to monitor temporal changes in catecholamine release from PC12 cells following stimulation with potassium.
In this work, we report a newly developed paper-based analytical device (PAD) for determining formaldehyde in foods. Formaldehyde (FA) is considered as a carcinogen and classified as a Type 2 ...hazardous substance but it is still illegally use as a preservative in many foods to prevent them from spoilage and increase storage time. Current technologies for quantifying FA in foods are expensive, require long analysis times and skill operators, and are difficult to use on-site with acceptable performance. Consequently, a simple, low-cost, portable, instrument-free measurement test is needed to provide affordable and rapid in-field quantification of FA in foods. The developed FA tests, referred to as the FormaSense™, measure FA by observing diameter of a circular pink ring on the paper that is directly proportional to the FA concentration without the interference of food color background problem hence, increasing the test performance. Printing technologies including wax and inkjet printers were employed to demonstrate highly reproducible and scalable fabrication of the paper-based tests. The results of FA analysis in food samples obtained from the FormaSense™ tests are agreeable with those obtained the standard titration methods with good recoveries in the range of 90–107%.
•Diameter-based readout paper devices for formaldehyde (FA) analysis in foods.•FA quantification in foods without interferences from food color background.•Highly scalable production of paper devices using inkjet-printing technology.
We report the first use of a paper-based device as a simple, low-cost and rapid detection platform for simultaneous determination of antioxidant activity and total phenolic content in food samples. ...Two antioxidant activity assays including 2,2′-azino-bis(3-ethylbenzthiazoline-6-sulphonate) radical cation (ABTS) assay and cupric reducing antioxidant capacity (CUPRAC) assay and one total phenolic content assay, Folin Ciocaltue reagent (FC) assay were simultaneously employed as a proof-of-concept. The device composed of a central sample zone connected to four pretreatment zones and consecutive detection zones to accommodate all three assays and a sample blank measurement. The analysis was achieved by dropping the samples onto the sample zone to flow to the pretreatment and detection zones containing the stored reagents for each antioxidant assay making the color change that was measured using imageJ software. Assay optimization including key reagent concentrations, reaction time, and surface modification were carried out to obtain sensitive and wide linear rage analyses. Various antioxidant standards were then evaluated to determine the analytical features of the method. The paper-based assays were successfully applied to detect antioxidant activity and total phenolic content in 10 beverage samples with similar gallic acid equivalent (GAE) values to those obtained from traditional assays at a 95% confidence interval. Moreover, the GAE values of the samples obtained from three assay analyses were well correlated to each other with relatively high Pearson's correlation coefficients. These results indicated that the assays gave accurate results and are suitable for simultaneous analysis of antioxidant activity and total phenolic content in real samples.
Display omitted
•Multiple antioxidant and total phenolic content assays can be performed simultaneously on a single PAD.•Various information on antioxidant mechanisms can be obtained in one analysis.•Rapid analysis with low reagent and sample consumption for multiple antioxidant analysis.
Cloth-based sensors are gaining attention for creating microfluidic wearable sensors for continuous monitoring of sweat biomarkers because of their flexibility, low cost, and natural hydrophilicity ...making them suitable for integration into everyday products. Here, we present a novel, low-cost and simple fabrication approach to create a cloth-based sensor ready for use as a sweat sensor while being environmentally friendly using biocompatible and biodegradable material, polylactic acid (PLA), and a stencil transparent film-printing method. The method provided high-resolution structures with narrowest hydrophilic channels and hydrophobic barriers measuring 1.90 ± 0.34 mm and 1.23 ± 0.14 mm, respectively. Various designs for detecting sweat biomarkers, including pH, lactate, and chloride, were generated by simply adjusting the stencil transparent film designs. For pH detection, a square-shaped cloth-based sensor was constructed and different natural indicators was used as biocompatible and non-toxic reagents to measure pH providing the detection in the pH range of 1–14. In lactate determination, an enzymatic assay with nanoceria as colorimetric probes was used in a spot format, offering a lactate detection range of 2.5–25 mM, effectively distinguishing between normal and abnormal muscle fatigue patients at a cut-off level of 12.5 mM sweat lactate. For chloride, a distance-based format was employed using the reverse Mohr titration assay, resulting in a detection range of 10–100 mM. Finally, the analysis of lactate and chloride in artificial sweat was successfully demonstrated yielding the recovery in the acceptable range demonstrating accurate measurements of the fabricated cloth-based sensors.
Display omitted
•PLA, a biocompatible, biodegradable polymer, was first used in creating a cloth-based sweat sensor.•A novel stencil transparent film-printing method was used to pattern PLA hydrophobic barrier onto the cloth.•The fabricated sensor effectively analyzed sweat biomarkers including pH, lactate, and chloride.
Display omitted
•The acid-base titration using μTAD was firstly developed for formalin analysis in food samples.•Distance of colored zone was analyzed by visual detection and a digital vernier ...caliper.•It provides easy and low-cost monitoring of formalin in various food samples.
The use of formalin (FA) to maintain food freshness and storage time is illegal. FA intake causes chronic and acute effects on human health. In this work, the novel visual detection of FA in food samples by using a microfluidic thread-based analytical device (µTAD) was developed. This proposed method based on a sulfite assay where FA reacted with excess Na2SO3 to generate NaOH that was quantified on µTAD using acid-base titration. The µTAD was fabricated from an untreated 100 % cotton thread (20.0 cm) treated with phenolphthalein solution as an indicator and low and high concentrations of Potassium hydrogen phthalate (KHP) as a limiting agent. Both threads were tied together with a central knot before being attached to the woodblock platform before the analysis. The length of the color change (colorless to pink) on the µTAD was analyzed by the visual detection using the digital vernier caliper and ImageJ software (mode: distance measurement) using a captured image from a smartphone. Two linear calibration curves at low concentration (150–350 mg L−1) and high concentration (500–900 mg L−1) were achieved with the limit of quantification at 150 mg L−1. In addition, greater selectivity towards FA compared with potential interference ions was also observed. Furthermore, the developed µTAD was applied to analyze FA in food samples, and the results was agree with those obtained by the conventional method. Thus, the proposed µTAD can be used for developing a colorimetric detection platform for interesting trace chemical analysis.
Particulate matter (PM) air pollution has a significant impact on human morbidity and mortality; however, the mechanisms of PM-induced toxicity are poorly defined. A leading hypothesis states that ...airborne PM induces harm by generating reactive oxygen species in and around human tissues, leading to oxidative stress. We report here a system employing a microfluidic electrochemical sensor coupled directly to a particle-into-liquid sampler (PILS) system to measure aerosol oxidative activity in an on-line format. The oxidative activity measurement is based on the dithiothreitol (DTT) assay, where, after being oxidized by PM, the remaining reduced DTT is analyzed by the microfluidic sensor. The sensor consists of an array of working, reference, and auxiliary electrodes fabricated in a poly(dimethylsiloxane)-based microfluidic device. Cobalt(II) phthalocyanine-modified carbon paste was used as the working electrode material, allowing selective detection of reduced DTT. The electrochemical sensor was validated off-line against the traditional DTT assay using filter samples taken from urban environments and biomass burning events. After off-line characterization, the sensor was coupled to a PILS to enable on-line sampling/analysis of aerosol oxidative activity. Urban dust and industrial incinerator ash samples were aerosolized in an aerosol chamber and analyzed for their oxidative activity. The on-line sensor reported DTT consumption rates (oxidative activity) in good correlation with aerosol concentration (R 2 from 0.86 to 0.97) with a time resolution of approximately 3 min.
Human exposure to particulate matter (PM) air pollution is associated with human morbidity and mortality. The mechanisms by which PM impacts human health are unresolved, but evidence suggests that PM ...intake leads to cellular oxidative stress through the generation of reactive oxygen species (ROS). Therefore, reliable tools are needed for estimating the oxidant generating capacity, or oxidative load, of PM at high temporal resolution (minutes to hours). One of the most widely reported methods for assessing PM oxidative load is the dithiothreitol (DTT) assay. The traditional DTT assay utilizes filter-based PM collection in conjunction with chemical analysis to determine the oxidation rate of reduced DTT in solution with PM. However, the traditional DTT assay suffers from poor time resolution, loss of reactive species during sampling, and high limit of detection. Recently, a new DTT assay was developed that couples a particle-into-liquid-sampler with microfluidic-electrochemical detection. This "on-line" system allows high temporal resolution monitoring of PM reactivity with improved detection limits. This study reports on a laboratory comparison of the traditional and on-line DTT approaches. An urban dust sample was aerosolized in a laboratory test chamber at three atmospherically relevant concentrations. The on-line system gave a stronger correlation between DTT consumption rate and PM mass (R
2
= 0.69) than the traditional method (R
2
= 0.40) and increased precision at high temporal resolution, compared to the traditional method.
Copyright 2014 American Association for Aerosol Research
Immunoassays are one of the most useful diagnostic techniques in disease assessment, drug metabolite analysis, and environmental applications due largely in part to the selectivity and sensitivity ...provided by antibody–antigen interactions. Here, a multiplexed immunoassay termed cleavable tag immunoassay (CTI) was performed in competitive, non-competitive, and mixed formats for the analysis of proteins and small molecule biomarkers of inflammation and tissue damage. Microchip capillary electrophoresis (MCE) with fluorescence detection was employed for the analysis of fluorescently labeled tags corresponding to the analytes of interest cleaved from the detection antibodies. For this work we have selected 3-nitrotyrosine (3-NT) a molecule indicative of reactive nitrogen species (RNS), thyroxine (T4) a molecule used to monitor thyroid gland function, and C-reactive protein (CRP) a marker of chronic inflammation as model analytes to demonstrate the assay principles. The simultaneous detection of 3-nitrotyrosine (3-NT) and thyroxine (T4) was carried out as a proof-of-principle for the competitive CTI while non-competitive CTI performance was demonstrated via the analysis of C-reactive protein (CRP). Limit of detections (LOD) and dynamic ranges were investigated. LOD for 3-NT, T4, and CRP were 0.5μg/mL, 23nM, and 5μg/mL, respectively thus demonstrating the ability of the CTI to detect proteins and small molecules within clinical reference ranges. Moreover, this is the first report of the use of mixed format CTI chemistry for the simultaneous detection of proteins (CRP) and small molecules (3-NT) in a single assay. The success of this work demonstrates the ability of CTI to analyze intact proteins and small molecule biomarkers simultaneously.
Extensive epidemiological studies show strong associations between the exposure to atmospheric aerosol particulate matter (PM) in the size range of 0.1–10 µm and health problems, including ...respiratory, atherosclerosis and cardiovascular diseases. However, the mechanisms of PM-induced toxicity are poorly understood. A leading hypothesis states that airborne PM induces harm by generating reactive oxygen species in and around human tissues, leading to oxidative stress. To improve understanding of this effect, methods including biological assays and chemical assays for assessing oxidative stress caused by atmospheric aerosols have been developed and are described in this dissertation. For biological assays, a cleavable tag immunoassay (CTI) was developed with an ultimate goal of measuring multiple oxidative stress biomarkers in a single run. As a proof-of-concept, the multianalyte analysis system CTI was performed in competitive, non-competitive, and mixed formats for detection of small molecules and protein biomarkers simultaneously. For chemical assays, a microfluidic electrochemical sensor and a microfluidic paper-based analytical device (µPAD) have been developed for assessing aerosol oxidative stress in an area-based exposure study and a personal exposure study, respectively. The microfluidic electrochemical sensor was used for assessing aerosol oxidative stress by measuring the oxidative activity. The sensor was coupled directly to a Particle-into-Liquid-Sampler (PILS) to create an on-line aerosol sampling/analysis system. The system offers analysis with 3 minute temporal resolution, making it the best available temporal resolution for aerosol oxidative activity. The sensor was also used to analyze the ability of aerosols to generate hydroxyl radicals as another parameter for assessing aerosol oxidative stress. The ultimate goal of this system is to create an on-line monitoring system using a similar approach for oxidative activity analysis. As a first step toward this goal, assay optimization and system characterization in an off-line format employing flow injection analysis and amperometric detection, were carried out and presented in this dissertation. A microfluidic paper-based analytical device (µPAD) was developed for measuring oxidative activity of aerosol collected by a personal sampler. The system allows analysis with minimal sample preparation and requires 100-fold less particulate matter mass than existing analysis methods.
The coronavirus (COVID-19) epidemic has had a significant impact on people's lives and businesses. After the epidemic situation, Saensuk Sub-district, Chonburi is one area that has a need to change ...its tourism management. Saen Suk Municipality launched a campaign to promote Bang Saen as a "Safe Food Avenue". The pilot project began with production of an application to support a special test for formalin (FA) in sea foods which shows the result to food shops and tourists online. The FA test kit was produced and approved with accurate test results verified by a team of specialists from Burapha university. The application was developed using a responsive website technique. Specialists used the system to upload images of FA test results. Then a machine learning in image processing technique was used to analyze the test results. The Server sends the result through a RESTFUL API in JSON format to the application so that users can see the results online. The experiment using Circular Hough Transform (CHT) algorithm to detect circular shape in two-dimensional space by voting in Hough parameter with 400 data records for training. Based on the FA test result dataset, training accuracy are 100%. The SafeFoodAvenue mobile application using responsive technology FA test result's dataset accuracy is 100%.
PDF
