Validation of quantitative loop-mediated isothermal amplification assay using a fluorescent distance-based paper device for detection of Escherichia coli in urine.

Uropathogenic Escherichia coli (UPEC) causes up to 90% of urinary tract infections (UTI) which is more prevalent among females than males. In urine, patients with symptomatic UTI usually have a high concentration of bacterial infection, ≥ 105 colony-forming units (CFU) per mL, in which the culture method is regularly the gold standard diagnosis. In this study, a simple and inexpensive distance-based paper device (dPAD) combined with the fluorescent closed tube LAMP assay was validated for simultaneously screening and semi-quantifying the infection level of E. coli in 440 urine samples of patients with UTI. The dPAD could measure the LAMP amplicons and semi-quantify the levels of E. coli infection in heavy (≥ 104 CFU/mL), light (≤ 103 CFU/mL) and no infection. The sensitivity and specificity had reliable performances, achieving as high as 100 and 92.7%, respectively. The one step LAMP assay could be performed within 3 h, which was 7.5 times faster than the culture method. To empower early UTI diagnosis and fast treatment, this inexpensive dPAD tool combined with the fluorescent closed tube LAMP assay is simple, reliably fast and practically portable for point-of-care settings, particularly in resource-limited areas, which can be set up in all levels of healthcare facilities.

A sensitive and facile electrochemical paper-based sensor for glucose detection in whole blood using the Pd/CB-Ni@rGO modified electrode.

We created novel Pd/CB-Ni@rGO nanomaterials for glucose detection. The as-synthesized nanomaterials were dropped on the electrode surface using the drop casting technique. The prepared electrode was then attached to a paper-based device containing the sample zone and the reaction zone, enabling plasma isolation and an enzymatic reaction for glucose detection in whole blood. The nanomaterials and surfaces of electrodes were characterized by FTIR, TEM, and SEM. The proposed approach is a disposable glucose detection method that is unaffected by protein fouling on the electrode, and it requires only one drop of human blood. Therefore, there is no need for extensive sample preparation, and there is less sample consumption. Under optimal conditions, Pd/CB-Ni@rGO can accurately measure blood glucose levels with a linear range of 7 to 7140 µM (R2 = 0.9986) and a low detection limit of 0.82 µM. Besides, the developed sensor shows excellent anti-interference capacity, stability, and satisfactory reproducibility and repeatability. Importantly, Pd/CB-Ni@rGO was successfully applied for glucose in whole blood from 4 volunteers, with results that correlated well with those obtained using an Accucheck glucometer at a 95% confidence level. Given its low cost, high accuracy, and ease of use, the blood glucose sensor holds significant potential for clinical use and broadens the area of future noninvasive sensor development.

Dual-mode ion-selective electrodes and distance-based microfluidic device for detection of multiple urinary electrolytes.

Here, we developed a microfluidic paper device by combining ion-selective electrodes (ISE) and a distance-based paper device (dPAD) for simultaneous potentiometric and colorimetric detection of urine electrolytes including K+, Na+ and Cl-. The working and reference electrode zones were coated with polystyrene as a non-ionic polymer to improve hydrophobic properties on the paper surface for fabrication of K+-ISE and Na+-ISE. The layer of polymer coating was optimized to enhance the sensitivity of the ISEs. Under optimized conditions, the electrode surfaces were modified with carbon black to improve the electrochemical characteristics of the ISEs. The ISEs showed good performance with sensitivities of 54.14 ± 3.94 mV per decade and 55.08 ± 1.15 mV per decade for K+ and Na+ within the linear concentration range 0.100 mM-100 mM K+ and 5 mM-1 M Na+, respectively. The limits of detection (LOD) were 0.05 mM and 1.36 mM for K+ and Na+, respectively. The linear working range of Cl- was 0.50 to 50 mM and the LOD and limit of quantification (LOQ) were found to be 0.16 ± 0.05 mM (3SD) and 0.53 ± 0.05 mM (10SD), respectively. The dual-mode ISE-dPAD was validated in human urine and recoveries were obtained as 90-108%, 94-105%, and 90-96% for K+, Na+, and Cl-, respectively, showing successful application of the developed device in a complex matrix. The ISE-dPAD has advantages including low-cost ($ 0.33 per test), eco-friendly, portability, simple operation, the need of low sample volume (100 µL), and simultaneous analysis on a single device.

A smartphone-assisted hybrid sensor for simultaneous potentiometric and distance-based detection of electrolytes.

At home electrolyte analysis is of growing interest due to the importance for early diagnosis for various diseases. This work presents the first device that integrates a potentiometric ion-selective electrode (ISE) with distance-based colorimetric detection for the simultaneous analysis of K+ and Cl- ions at the point of care (POC). This hybrid sensing device was designed in a two-dimensional configuration using a plastic transparency sheet containing a stencil printed K+-ISE and a paper substrate for distance-based colorimetric detection of Cl-. K+ quantification was performed using a low-cost (<$25) lab-made Wi-Fi supported potentiometer with a custom smartphone application while Cl- ions were quantified with an instrument-free distance-based paper analytical device (dPAD). The total analysis time is 5 min once the sample is added. The K+-ISE showed a sensitivity of 55.89 ± 2.52 mV/decade from 0.1 to 100 mM with a limit of detection (LOD) of 0.01 mM. The linear working range for Cl- detection was 0.5-50 mM whereas the LOD was 0.16 ± 0.05 mM. The proof-of-concept application of the sensing hybrid device was demonstrated in human urine and artificial sweat samples containing K+ and Cl- ions at physiologically relevant ranges. The recoveries were found to be 88-108% for K+ and 90-104% for Cl-, showing the potential use of the proposed device for low-cost routine analysis of biological samples at POC.

Distance-based paper device using combined SYBR safe and gold nanoparticle probe LAMP assay to detect Leishmania among patients with HIV.

Asymptomatic visceral leishmaniasis cases increase continuously, particularly among patients with HIV who are at risk to develop further symptoms of leishmaniasis. A simple, sensitive and reliable diagnosis is crucially needed due to risk populations mostly residing in rural communities with limited resources of laboratory equipment. In this study, a highly sensitive and selective determination of Leishmania among asymptomatic patients with Leishmania/HIV co-infection was achieved to simultaneously interpret and semi-quantify using colorimetric precipitates (gold-nanoparticle probe; AuNP-probe) and fluorescence (SYBR safe dye and distance-based paper device; dPAD) in one-step loop-mediated isothermal amplification (LAMP) assay. The sensitivities and specificities of 3 detection methods were equivalent and had reliable performances achieving as high as 95.5%. Detection limits were 102 parasites/mL (0.0147 ng/µL) which were 10 times more sensitive than other related studies. To empower leishmaniasis surveillance as well as prevention and control, this dPAD combined with SYBR safe and gold nanoparticle probe LAMP assay is reliably fast, simple, inexpensive and practical for field diagnostics to point-of-care settings in resource-limited areas which can be set up in all levels of healthcare facilities, especially in low to middle income countries.

Distance-Based All-In-One Immunodevice for Point-of-Care Monitoring of Cytokine Interleukin-6.

We report the development of a distance-based paper analytical device combined with a hydrophilic bridge valve (B-dPAD) as a quantitative immunoassay method to monitor human interleukin-6 (IL-6) in human samples. Our device design features (i) a circular sample inlet zone, (ii) a circular capture zone with immobilized anti-IL-6 (anti-Ab1), and (iii) a detection zone channel coated with methylene blue (MB). Two hydrophilic valves are positioned between these three zones. IL-6 levels were determined quantitatively by measuring the extent of degradation of MB to a colorless product along the length of the detection zone channel. Following method optimization, we obtained a linear range from 0.05 to 25.0 pg/mL (R2 = 0.9995) and a detection limit (LOD) of 0.05 pg/mL by the naked-eye readout. This is directly within the clinically relevant range. The system does not require any external instrumentation, and the bridge valves can be easily connected and disconnected by a minimally trained operator. The total analysis time is 35 min, significantly reduced from a typical ELISA assay, which takes around 1 h since the B-dPAD workflow circumvents washing steps. The device was tested for IL-6 quantification in human saliva and urine samples of volunteers, with no significant difference found between our method and the standard clinical laboratory method at 95% confidence levels. Recoveries ranged from 98 to 105% with the highest standard deviation at 3.9%. Our B-dPAD immunodevice is therefore a promising approach for rapid IL-6 monitoring in the context of point-of-care diagnostics and analysis in resource-limited settings.

A Simple Counting-Based Measurement for Paper Analytical Devices and Their Application.

This work introduces the concept of a counting-based measurement on paper analytical devices (cPADs) to improve the utilization of numerous reactions. The design of cPADs consists of two layers of paper substrates; the first layer contains a central sample zone combined with a radial surrounded by 12 detection zones that are predeposited with the various reagents, and the second layer acts as a connection channel between the sample zone and each detection zone. The solution can vertically flow from the first to the second layer and then move through the area to each subsequent detection zone. The analyte level can be evaluated by counting the number of detection zones that change color from a blank signal. Furthermore, our cPADs exhibit a capability of implementation for a broad series of reactions. Compared to the dPAD technique, some reactions that are possibly difficult to apply in such devices can be wholly enabled in our devices. The final color reaction on cPADs can apparently occur due to its identity. We applied this technique to the monitoring of carbaryl (CBR) and copper ions (Cu2+) using different reactions, including azo-coupling and complexation, respectively. Accordingly, this indicates an excellent result validated using the more traditional methods. Our cPADs can be applied for rapid screening of both CBR and Cu2+ in water samples with outstanding accuracy and precision using a naked-eye measurement by a relatively unskilled person. We offer a simple platform on PADs for rapid screening, combining high cost-effectiveness within a miniaturized platform designed for use with onsite applications, which is thus suitable for several different reactions.

Distance-based ß-amyloid protein detection on PADs for the scanning and subsequent follow-up of Alzheimer's disease in human urine samples.

We report on the first development of a simple distance-based ß-amyloid (Aß) protein quantification using a paper-based device (dPAD) to screen for Alzheimer's disease (AD) and to subsequently follow up on its influence, i.e., clinical dementia. This sensor method is based on the transformation of a free acid form and its binding with a basic form of bromocresol purple (BCP) through its electrostatic interaction with an Aß protein. This sensor can measure the length of color change from yellow to blue-green on a paper strip, with this change proportional to the amount of Aß protein level. We found that the linearity for Aß protein monitoring was in the range from 0.50 to 10.0 ng mL-1, and the subsequent naked-eye detection limit for Aß was 0.20 ng mL-1. This system also provided high reproducibility and with no apparent interference effect for Aß protein analysis in human urine samples. Furthermore, our developed dPAD constituted an accurate and effective device to precisely determine an Aß protein concentration in real samples, with percentage recoveries in the range of 97-103%, and with the highest relative standard deviation of 5.41%. Subsequently, the validation of our assay was assessed by comparison with a commercial ELISA approach, with favorable results. Finally, the proposed dPAD was successfully applied to the determination of an Aß protein in human urine samples and showed more benefits for the unskilled user, such as cost-efficiency, simplicity, low reagent usage, and low time consumption. It is also suitable for point-of-care monitoring.

Distance-Based Paper Device for a Naked-Eye Albumin-to-Alkaline Phosphatase Ratio Assay.

The albumin-to-alkaline phosphatase ratio (AAPR) has been a cancer prognostic indicator. This paper presents the concept of a dual-color change distance-based paper device (dPAD) for albumin (Alb) and alkaline phosphatase (ALP) detection to evaluate this cancer prognostic index. Whereas Alb interacts with the bromocresol green (BCG) indicator to form a bluish-green complex, ALP hydrolyzes l-ascorbic acid-2-phosphate (AAP) to produce ascorbic acid (AA), which reacts with KIO3 to generate I2 and I-. I2/I- reacts with silver hexagonal nanoprisms (purple color) in the presence of Cu2+, resulting in a color change from purple to colorless. The distance of the color change from yellow to the bluish-green and purple to colorless correlates to Alb and ALP concentration, respectively. The angle index for the AAPR is then defined by drawing a straight line that connects the tops of the two changed band lengths in the detection area. The highest bluish-green color band length on the Alb region is the midpoint, which is the position set of the protractor at 0°, and the angle is measured using a simple protractor. The results indicate that an AAPR below 0.57 will have an angle greater than 40° and correlates with a risk factor for lung cancer. The naked-eye detection limits for Alb and ALP were found to be 0.8 g/L and 5 U/L (n = 10), respectively. The practical application of the developed dPAD was successfully demonstrated by Alb and ALP analysis in human serum and validated against standard methods. The proposed method does not require incubation conditions for the ALP assay, which strongly reduces the overall analysis steps and time. Moreover, our device provides a low-cost, simple, sensitive, selective, accurate, and precise determination of the AAPR.

Highly sensitive distance-based liquid crystalline visualization for paper-based analytical devices.

We successfully report on the first demonstration of a highly sensitive distance-based liquid crystalline visualization for paper-based analytical devices. The construction of this paper sensor was achieved by immobilizing 4-cyano-4'-pentylbiphenyl (5CB) as liquid crystalline molecules (LCs) onto a paper strip substrate. The sensing mechanism is based on the ultrasound-assisted decomposition of 5CB by the hydroxyl radical (•OH) which is generated from the oxidase enzymatic reaction of the analyte, this then results in the change of texture and color of paper. The utility of our devices was then demonstrated with the determination of bilirubin (BR) in biological samples using a bilirubin oxidase enzymatic reaction. The quantification of BR can be achieved by dipping the tip of the paper strips into the analyte solutions and then by measuring the length of color which has been changed on the paper, by the naked eye. Under optimized conditions, this paper sensor offered the linear range of BR detection from 2.0 to 30.0 pmol/L (R2 = 0.9945) with the limit of detection (LOD) of 0.80 pmol/L. In addition, the results of this sensor were highly reproducible, with a relative standard deviation (RSD) of less than 3.50%. The recoveries of spiked BR in human urine and serum samples were in the range of 99.09-107.89%, which demonstrates the high accuracy of this paper sensor. Overall, this work presents a simple method to determine the concentration of H2O2 and BR at pmol levels with an instrument-free length-measuring readout, so it could be suitable for quantitative analysis of other biomarkers based on oxidase enzymatic reaction, which can provide important information about early disease diagnosis and patient prognosis.

A rapid and highly sensitive paper-based colorimetric device for the on-site screening of ammonia gas.

A rapid and highly sensitive paper-based colorimetric device for the on-site detection of ammonia (NH3) gas is presented in this study. The detection principle of this device is based upon a change of color from red to yellow on a paper that has been immobilized with a pH indicator, i.e., methyl orange (pKa = 3.4), in the presence of NH3 gas. The color signal of the device can be measured through the hue channel of an HSL system via the application of a smartphone. This device can detect the amount of NH3 gas within 3 min. The linear relationship between the NH3 gas concentration and the hue signal was found to be in the range from 6.0 to 54.0 ppbv with R2 = 0.9971, and the limit of detection was found to be 2.0 ppbv. In addition, this device showed remarkably high selectivity to NH3 gas amongst the other common volatile organic compounds and general gases that are present in environmental air without the assistance of any membrane material. Furthermore, we demonstrated the applicability of this device for the detection of total NH3 gas at a chicken farm and in a laboratory, with relative standard deviations of 6.2% and 5.4%, respectively. The developed NH3 gas device in the study is easy to operate and cost-effective, with the reduction of a large consumption of chemical reagents; also, its signals can be measured simply and then recorded through a smartphone. It is suitable for the application of routine on-site detection of NH3 gas, especially concerning regions which have limited resources.

Rapid Distance-Based Cardiac Troponin Quantification Using Paper Analytical Devices for the Screening and the Follow-Up of Acute Myocardial Infarction, Using a Single Drop of Human Whole Blood.

This work introduces the procedure of using non-immunoassay distance-based paper analytical devices (dPADs) to accurately measure any traces of the cardiac troponin I (TnI) in whole blood samples without the use of any external blood separation. This enables a rapid clinical diagnosis and the subsequent follow-up in regard to identifying acute myocardial infarction. These dPADs are designed and constructed to accommodate three parts: (1) a blood separation zone that is immobilized with a hemostatic agent, this no longer requires a blood separation membrane for the isolation of the plasma from the blood element, (2) a pretreatment zone, and (3) a detection zone coated with thymol blue. The quantitative TnI level in the whole blood was determined by measuring the blue color length found in the detection zone, which is proportional to the concentration, owing to the dry protein binding principle. Correspondingly, a mere single drop of human whole blood performs adequately within our proposed method. This reduces both the size of the collection process and the sample volumes needed in the respective medical fields. As we cover all of the optimization studies, our dPADs provide an evaluation of the linearity range from 0.025 to 2.5 ng/mL (R2 = 0.9989) of TnI, with a detection limit as low as 0.025 ng/mL by use of an observation just using the naked eye. To validate the clinical utilities of our proposed method, our dPADs were then applied for the detection of TnI in humans using the whole blood sample of 15 volunteers. A great amount of accuracy was required in this assay because there was no significant difference between both methods, with the confidence level being as high as 95%. This technique also showed that the recoveries ranged from 99.40 to 104.27%, with the highest relative standard deviation being at 3.77%. Thus, our proposed dPADs offer more benefits for a rapid TnI determination.

A Portable Reflective Absorbance Spectrophotometric Smartphone Device for the Rapid and Highly Accurate Determination of Amlodipine in Pharmaceutical Formulation and Human Urine Samples.

The simple reflective absorbance spectrophotometric smartphone device for point-of-monitoring amlodipine is presented here for the first time. The immediate analysis of amlodipine in the human urine of the patients who suffered severe side effects of this drug is very important for the diagnosis, treatment, and reduction of the death rate. This measurement technique is based on the charge-transfer complex between amlodipine and picric acid, which forms a yellow product. This product can absorb light intensity from an LED strip and measure through the Blue channel from the RGB mode with a smartphone application. The linear relationship for amlodipine monitoring was found in a wide range from 100.0 µg L-1 to 140.0 mg L-1 (R2 = 0.999), and the limit of detection was found to be 25.0 µg L-1. Our proposed method can be applied to different smartphone brands with consistent sensitivity of amlodipine detection. Additionally, the determination of amlodipine in pharmaceutical formulations and human urine samples was demonstrated by our proposed method. The recoveries were indicated in the range of 98.60 - 100.00%, which is at the acceptable level for pharmacy. This method offers an interweaving of basic technology and chemical analysis with being environmentally friendly due to reducing the complex instrument and the amount of organic waste compared to the chromatographic technique and efficient use for the detection of amlodipine. Hence, this method can be applied for prompt medical diagnoses and laboratories with limited budget resources.

Highly sensitive, selective and naked-eye detection of bromide and bromate using distance-based paper analytical device.

Bromine (Br) can usually be found as a bromide (Br‾) form contained in drinking water. Bromate (BrO3‾) formation often occurred during the ozonation process in the presence of Br‾. BrO3‾ is classified as a potential human carcinogen, so both the Br‾ and BrO3‾ concentrations must be strictly controlled before and after an ozone-based treatment procedure, respectively. This work reports on distance-based paper analytical devices (dPADs) that have been modified with silver hexagonal nanoprisms (AgNPrs) for highly sensitive and selective determination of both Br‾ and BrO3‾. The measurement of BrO3‾ is based upon its conversion to bromine vapor (Br2) when gauged with a paper-based headspace extractor (PAD-HS) that is coupled with dPADs (PAD-HS-dPADs). For Br‾ analysis, O2 plays an important role in the change from Br‾ to Br2 within an acid media. Br2 changes rapidly in water to give us HBrO which is a strong oxidizing agent of AgNPrs. Then, the oxidative reaction of the AgNPrs (pink color) within the presence of Br‾ and BrO3‾ establishes both silver bromide (AgBr) and the silver nanosphere (AgNPs, yellow color), which can then be easily observed as a change of a pink color band to a yellow color band by the naked eye. Quantification of Br‾ and BrO3‾ is then achieved by measuring the length of the yellow color band. Under the optimal conditions, the calibration curve will be linear in the range of 25 µg L-1 to 2 mg L-1, and from 0.5 to 50 µg L-1 for Br‾ and BrO3‾, respectively. The naked-eye detection limits were found to be 10 and 0.5 µg L-1 for Br‾ and BrO3‾, respectively. The proposed dPADs for the Br‾ and BrO3‾ detection exhibited an exceptional sensor performance combined with a low detection limit. They also have the benefits of ease of use, an instrument-free convenience, coupled with portability and a low-cost efficiency. Consequently, our sensing device should be applied to the low-level detection of Br‾ and BrO3‾ in real samples, including drinking water, rice, and flour.

Development of a fluorescent distance-based paper device using loop-mediated isothermal amplification to detect Escherichia coli in urine.

The highly sensitive and selective determination of Escherichia coli (E. coli) in urine was achieved using a SYBR™ safe loop-mediated isothermal amplification (LAMP) method with a distance-based paper device. New primers set specific to multi-copy the 16s rRNA gene of E. coli were designed and used in this study. The detection sensitivity of these primers was higher than in related work and they could be incorporated with a low-cost paper-based device to quantify E. coli in urine at a concentration lower than 101 CFU mL-1. Regarding standard artificial urine, a linear range of a 10-fold dilution of E. coli concentration (105-100 CFU mL-1) with an R-square value (R2) = 0.9823 was observed directly using a fluorescent migratory distance of the 4 µL reaction mixture in the detection zone under blue light without the need for postreaction staining process. Based on the device, E. coli infection could be significantly categorized into 3 groups; none, light, and heavy levels, which is beneficial for UTI diagnosis. Hence, this paper-based device is suitable for use with the SYBR™ Safe-LAMP assay to semi-quantify E. coli, especially in resource-limited settings due to advantages of low cost, simple fabrication and operation, and no requirement for sophisticated instruments, as well as its disposability and portability.

Dual Sample Preconcentration for Simultaneous Quantification of Metal Ions Using Electrochemical and Colorimetric Assays.

A paper-based method for heating preconcentration (PAD-HP) has been developed for the determination of Pb2+, Cd2+, Fe3+, and Ni2+. The design of our heating system was evaluated for dual quantification of ions using electrochemical and colorimetric methods simultaneously. The PAD-HP was used to detect Pb2+ and Cd2+ by anodic stripping voltammetry and to detect Fe3+ and Ni2+ by colorimetric reactions. Assay conditions were optimized by evaluating performance when changing the concentration of the colorimetric reagent, eluent volume, electrolyte concentration, and electrochemical parameters. Limits of detection (LOD) were determined to be 0.97 and 2.33 µg L-1 for Pb2+ and Cd2+ (via voltammetry) and 0.03 and 0.04 mg L-1 for Fe3+ and Ni2+ (via colorimetric assay), respectively. The relative standard deviations for assays were in the range of 5.76 to 10.12%. We observed that the PAD-HP method significantly enhanced the signal of all metals ions (14-100-fold, depending on the metal) in comparison to paper-based devices that did not use a heating preconcentration system. This PAD-HP method was successfully applied to the determination of metals ions in samples of drinking water, tap water, pond water, and wastewater. These results suggest that our approach can provide a convenient strategy to monitor aqueous samples for heavy metals with high sensitivity and selectivity.

A paper-based conductive immunosensor for the determination of Salmonella Typhimurium.

We report for the first time a highly sensitive and rapid quantitative method for the detection of Salmonella Typhimurium (S. Typhimurium) using a conductive immunosensor on a paper-based device (PAD). S. Typhimurium monoclonal antibodies (MA) were first immobilized on a paper-based device and then captured by S. Typhimurium. After an immunoreaction on the device, the polyclonal antibody-colloidal gold conjugate (PA-AuNPs) was dropped to bind with S. Typhimurium. After a complete sandwich reaction, a dark red color appeared on the paper-based device, which can be observed by the naked eye for a rapid screening test. The electrical conductivity of PA-AuNPs between the screen-printed electrodes on the paper-based device was also measured for an accurate quantitative analysis. The electrical conductivity correlated well with the concentration of S. Typhimurium, which was controlled by the amount of S. Typhimurium attached to the polyclonal antibody-colloidal gold conjugate. The device showed a linear correlation for the concentration of the S. Typhimurium in the range of 10-108 CFU mL-1 in a logarithmic plot, with an R2 value of 0.9882 and a limit of detection (LOD) as low as 10 CFU mL-1. This simple, highly sensitive, and rapid method for the S. Typhimurium detection was successfully performed within 30 min, and it can be developed into small portable measuring devices in order to facilitate preliminary screening tests.

Sensitive distance-based paper-based quantification of mercury ions using carbon nanodots and heating-based preconcentration.

This article reports the first fluorescent distance-based paper device coupled with an evaporating preconcentration system for determining trace mercury ions (Hg2+) in water. The fluorescent nitrogen-doped carbon dots (NCDs) were synthesized by a one-step microwave method using citric acid and ethylenediamine. The fluorescence turn-off of the NCDs in the presence of Hg2+ was visualized with a common black light, and the distance of the quenched fluorescence correlated to Hg2+ concentration. The optimal conditions for pH, NCD concentration, sample volume, and reaction time were investigated. Heating preconcentration was used to improve the detection limits of the fluorescent distance-based paper device by a factor of 100. Under the optimal conditions, the naked eye limit of detection (LOD) was 5 µg L-1 Hg2+. This LOD is sufficient for monitoring drinking water where the maximum allowable mercury level is 6 µg L-1 as established by the World Health Organization (WHO). The fluorescent distance-based paper device was successfully applied for Hg2+ quantification in water samples without interference from other cations. The proposed method provides several advantages over atomic absorption spectroscopy including ease of use, inexpensive material and fabrication, and portability. In addition, the devices are simple to fabricate and have a long shelf-life (>5 months).

Development of an ultrasound-enhanced smartphone colorimetric biosensor for ultrasensitive hydrogen peroxide detection and its applications.

In this work, we developed the first ultrasound technique enhanced smartphone application for highly sensitive determination of hydrogen peroxide (H2O2). The measurement technique is based on the change in color intensity due to the transformation of tetramethylbenzidine (TMB) to oxidized tetramethylbenzidine (oxTMB) by the oxidation process with hydroxyl radical (OH˙) from the oxidation etching of silver nanoparticles (AgNPs) and its ultrasound usability. The oxTMB product occurs without peroxidase and can be detected with a saturation channel using HSV methodology via the application of a smartphone. To prove the peroxidase mimic property, our proposed method was also validated by determination of certain biomolecules, including glucose, uric acid, acetylcholine and total cholesterol, of which the known amounts are a valuable diagnostic tool. The proposed method provided the lowest limits of detection (LOD) of 2.0, 5.0, 12.50, 7.50, and 10.0 nmol L-1 for H2O2, glucose, uric acid, acetylcholine, and cholesterol, respectively, when compared with LODs obtained from other smartphone colorimetric methods. Reproducibility was calculated from the detection of H2O2 at 25.0 and 50.0 nmol L-1 with the highest standard deviations of 3.47 and 4.58%, respectively. Additionally, the determination of all analytes in human urine samples indicated recoveries in the range of 96-104% with the highest relative standard deviation of 3.98%, offering high accuracy and precision. Our research shows the novel compatibility of basic technology and chemical methodology with green chemistry principles by reducing a high-power process and organic solvent as well as exhibiting good colorimetric performance and effective sensitivity and selectivity. Thus, our developed method can be applied for point-of-care medical diagnosis.

Cotton fiber-based assay with time-based microfluidic absorption sampling for point-of-care applications.

Aim: Time-based microfluidic absorption sampling was proposed using cotton fiber-based device made in swab stick. The assay was optimized and compared with conventional pipetted drop sampling using the same device. Materials & methods: Reagents were integrated into cotton fiber device for assessing concentration of analytes by the colorimetric detection method through time-based absorption sampling microfluidic system. All assay parameters were first optimized using conventional pipette-based drop sampling. Results: The color intensity is linear in the relevant concentration range of the analytes. The LOD are 0.189 mM for glucose and 6.56 µM for nitrite, respectively. These values are better than conventional drop sampling. The fiber-containing swab itself functions as sampling, assay and calibration device. Conclusion: Microfluidic cotton fiber-based assay device was fabricated and can determine analyte concentration in artificial salivary samples, colorimetrically, by time-based absorption sampling without the need of complex equipments.