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.

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.

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 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.

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.

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.

Distance-Based Paper Device Combined with Headspace Extraction for Determination of Cyanide.

We report for the first time a distance-based paper device based on gold/silver core shell nanoparticles (Au@Ag NPs) for a simple, inexpensive, instrument-free, and portable determination of cyanide by the naked eye. Au@Ag NPs immobilized on a paper channel were etched by cyanide ions so that a yellow color band length of Au@Ag NPs is proportional to a decrease in the cyanide concentration. Quantification is achieved by measuring color length, thus eliminating the need to differentiate hues and intensities by the user, and the processing data of each imaging device. Moreover, the paper-based headspace extraction was combined with the distance-based paper device to improve the sensitivity. The enrichment factor was found to be 30-fold and the linearity was found in the range 0.05-1 mg L-1. The naked eye detection limit was 10 µg L-1 where the World Health Organization (WHO) have regulated the maximum level of cyanide in drinking water as 70 µg L-1. Our proposed device also showed no interference from common cations and anions presenting in seawater and waste water including thiocyanate, chloride. Finally, our device has been successfully applied to determine cyanide ions in seawater, drinking water, tap water and wastewater providing satisfactory precision and accuracy.

A distance-based paper sensor for the determination of chloride ions using silver nanoparticles.

We report for the first time the development of a distance-based paper sensor for a simple, inexpensive, instrument-free, and portable determination of chloride ions. Our analysis reaction is based on the oxidative etching of silver nanoparticles (AgNPs) to form AgCl in the presence of Cl- and H2O2. H2O2 reacts with AgNPs in the channel of the paper device and Cl- in the sample forming a white precipitate (AgCl) where the white color band length is proportional to the Cl- concentration. Quantification of Cl- is achieved by measuring the length of the white color band using a ruler printed on the side of the channel. Under optimal conditions, the distance-based paper sensor was characterized by a working range of 25-1000 mg L-1 (R2 = 0.9954) and the naked eye detection limit (LOD) was 2 mg L-1 (0.08 µg). Our sensor was found to be reproducible with a relative standard deviation of less than 4.51% (n = 10). The levels of Cl- in real water samples measured using our proposed device were within the error of the values measured using traditional tests but without the need for any external instrumentation. Therefore, our proposed method presents acceptable accuracy, precision, and high selectivity for point of need monitoring of Cl- in real water samples.

Multilayer paper-based device for colorimetric and electrochemical quantification of metals.

The release of metals and metal-containing compounds into the environment is a growing concern in developed and developing countries, as human exposure to metals is associated with adverse health effects in virtually every organ system. Unfortunately, quantifying metals in the environment is expensive; analysis costs using certified laboratories typically exceed $100/sample, making the routine analysis of toxic metals cost-prohibitive for applications such as occupational exposure or environmental protection. Here, we report on a simple, inexpensive technology with the potential to render toxic metals detection accessible for both the developing and developed world that combines colorimetric and electrochemical microfluidic paper-based analytical devices (mPAD) in a three-dimensional configuration. Unlike previous mPADs designed for measuring metals, the device reported here separates colorimetric detection on one layer from electrochemical detection on a different layer. Separate detection layers allows different chemistries to be applied to a single sample on the same device. To demonstrate the effectiveness of this approach, colorimetric detection is shown for Ni, Fe, Cu, and Cr and electrochemical detection for Pb and Cd. Detection limits as low as 0.12 µg (Cr) were achieved on the colorimetric layer while detection limits as low as 0.25 ng (Cd and Pb) were achieved on the electrochemical layer. Selectivity for the target analytes was demonstrated for common interferences. As an example of the device utility, particulate metals collected on air sampling filters were analyzed. Levels measured with the mPAD matched known values for the certified reference samples of collected particulate matter.

Determination of aerosol oxidative activity using silver nanoparticle aggregation on paper-based analytical devices.

Airborne particulate matter (PM) pollution significantly impacts human health, but the cellular mechanisms of PM-induced toxicity remain poorly understood. A leading hypothesis on the effects of inhaled PM involves the generation of cellular oxidative stress. To investigate PM-induced oxidative stress, analytical methods have been developed to study the chemical oxidation of dithiothreitol (DTT) in the presence of PM. Although DTT readily reacts with several forms of reactive oxygen species, this molecule is not endogenously produced in biological systems. Glutathione (GSH), on the other hand, is an endogenous antioxidant that is produced throughout the body and is directly involved in combating oxidative stress in the lungs and other tissues. We report here a new method for measuring aerosol oxidative activity that uses silver nanoparticle (AgNP) aggregation coupled to glutathione (GSH) oxidation in a paper-based analytical device. In this assay, the residual reduced GSH from the oxidation of reduced GSH to its disulfide induces the aggregation of AgNPs on a paper-based analytical device, which produces a reddish-brown product. Two methods for aerosol oxidative reactivity are presented: one based on change in color intensity using a traditional paper-based techniques and one based on the length of the color product formed using a distance-based device. These methods were validated against traditional spectroscopic assays for DTT and GSH that employ Elman's reagent. No significant difference was found between the levels measured by all three GSH methods (our two paper-based devices and the traditional method) at the 95% confidence level. PM reactivity towards GSH was less than towards DTT most likely due to the difference in the oxidation potential between the two molecules.

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.

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 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.

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 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.

A low-cost, simple, and rapid fabrication method for paper-based microfluidics using wax screen-printing.

Wax screen-printing as a low-cost, simple, and rapid method for fabricating paper-based microfluidic devices (µPADs) is reported here. Solid wax was rubbed through a screen onto paper filters. The printed wax was then melted into the paper to form hydrophobic barriers using only a hot plate. We first studied the relationship between the width of a hydrophobic barrier and the width of the original design line. We also optimized the heating temperature and time and determined the resolution of structures fabricated using this technique. The minimum width of hydrophilic channel and hydrophobic barrier is 650 and 1300 µm, respectively. Next, our fabrication method was compared to a photolithographic method using the reaction between bicinchoninic acid (BCA) and Cu(1+) to demonstrate differences in background reactivity. Photolithographically defined channels exhibited a high background while wax printed channels showed a very low background. Finally, the utility of wax screen-printing was demonstrated for the simultaneous determination of glucose and total iron in control human serum samples using an electrochemical method with glucose oxidase and a colorimetric method with 1,10-phenanthroline. This study demonstrates that wax screen-printing is an easy-to-use and inexpensive alternative fabrication method for µPAD, which will be especially useful in developing countries.

Poly(dimethylsiloxane) cross-linked carbon paste electrodes for microfluidic electrochemical sensing.

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.

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.