Poomrat Rattanarat

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

Nanoparticle-based electrochemical detection in conventional and miniaturized systems and their bioanalytical applications: A review

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.

Sodium dodecyl sulfate-modified electrochemical paper-based analytical device for determination of dopamine levels in biological samples

With recent advances in nanotechnology making more easily available the novel chemical and physical properties of metal nanoparticles (NPs), these have become extremely suitable for creating new sensing assays. Many kinds of NPs, including metal, metal-oxide, semiconductor and even composite-metal NPs, have been used for constructing electrochemical sensors. This article reviews the progress of NP-based electrochemical detection in recent applications, especially in bioanalysis, and summarizes the main functions of NPs in conventional and miniaturized systems. All references cited here generally show one or more of the following characteristics: a low detection limit, good signal amplification and simultaneous-detection capabilities.

A microfluidic paper-based analytical device for rapid quantification of particulate chromium.

We report the development of an electrochemical paper-based analytical device (ePAD) for the selective determination of dopamine (DA) in model serum sample. The ePAD device consists of three layers. In the top layer, SU-8 photoresist defines a hydrophilic sample application spot on the filter paper. The middle layer was made from transparency film and contained two holes, one for sample preconcentration and the other for the surfactant to allow transfer to the third layer. A screen-printed carbon electrode formed the bottom layer and was used for electrochemical measurements. In the absence of the anionic surfactant, sodium dodecyl sulfate (SDS), the oxidation peaks of DA, ascorbic acid (AA) and uric acid (UA) overlapped. With the addition of SDS, the DA oxidation peak shifted to more negative values and was clearly distinguishable from AA and UA. The oxidation potential shift was presumably due to preferential electrostatic interactions between the cationic DA and the anionic SDS. Indeed, whilst the SDS-modified paper improved the DA current five-fold, the non-ionic Tween-20 and cationic tetradecyltrimethylammonium bromide surfactants had no effect or reduced the current, respectively. Furthermore, only the SDS-modified paper showed the selective shift in oxidation potential for DA. DA determination was carried out using square-wave voltammetry between -0.2 and 0.8 V vs. Ag/AgCl, and this ePAD was able to detect DA over a linear range of 1-100 μM with a detection limit (S/N=3) of 0.37 μM. The ePAD seems suitable as a low cost, easy-to-use, portable device for the selective quantitation of DA in human serum samples.

Ultra-performance liquid chromatography coupled with graphene/polyaniline nanocomposite modified electrode for the determination of sulfonamide residues.

Occupational exposure to Cr is concerning because of its myriad of health effects. Assessing chromium exposure is also cost and resource intensive because the analysis typically uses sophisticated instrumental techniques like inductively coupled plasma-mass spectrometry (ICP-MS). Here, we report a novel, simple, inexpensive microfluidic paper-based analytical device (μPAD) for measuring total Cr in airborne particulate matter. In the μPAD, tetravalent cerium (Ce(IV)) was used in a pretreatment zone to oxidize all soluble Cr to Cr(VI). After elution to the detection zone, Cr(VI) reacts with 1,5-diphenylcarbazide (1,5-DPC) forming 1,5-diphenylcarbazone (DPCO) and Cr(III). The resulting Cr(III) forms a distinct purple colored complex with the DPCO. As proof-of-principle, particulate matter (PM) collected on a sample filter was analyzed with the μPAD to quantify the mass of total Cr. A log-linear working range (0.23-3.75 μg; r(2)=0.998) between Cr and color intensity was obtained with a detection limit of 0.12 μg. For validation, a certified reference containing multiple competing metals was analyzed. Quantitative agreement was obtained between known Cr levels in the sample and the Cr measured using the μPAD.

Glutathione and l-cysteine modified silver nanoplates-based colorimetric assay for a simple, fast, sensitive and selective determination of nickel

An ultra-performance liquid chromatography (UPLC) coupled with graphene/polyaniline (G/PANI)-modified screen-printed carbon electrode was developed for separation and sensitive determination of eight sulfonamides (SAs) in shrimp. Electrospraying was selected for electrode modification because it can generate the well dispersion of G/PANI nanocomposites on the electrode surface. Prior to electrochemical detection, eight SAs were completely separated within 7 min by using reversed phase UPLC (C4) with mobile phase containing 70:25:5 (v/v/v) of potassium hydrogen phosphate (pH 3):acetonitrile:ethanol. For amperometric detection, the detection potential acquired from hydrodynamic voltammetry was found to be +1.4V. Under optimal conditions, a wide linearity and low limit of detection were obtained for eight SAs in the range of 0.01-10 µg mL(-1) and 1.162-6.127 ng mL(-1), respectively. Compared to boron-doped diamond (BDD) electrode, a G/PANI-modified screen-printed carbon electrode offered higher sensitivity with lower operating cost. To determine SAs in shrimp samples, solid-phase extraction was used to clean up and preconcentrate the samples prior to UPLC separation. To validate this developed method, a highly quantitative agreement was accomplished with UPLC-UV system. Thus, this proposed system might be an alternative approach for rapid, inexpensive, and sensitive determination of SAs in shrimps.

Ultra-high performance liquid chromatographic determination of antioxidants in teas using inkjet-printed graphene–polyaniline electrode ☆

A novel colorimetric assay based on silver nanoplates (AgNPls) for detecting nickel ions (Ni(2+)) has been developed. Glutathione (GSH) and l-cysteine (Cys) were used to modify the AgNPls surface, exhibiting extremely high selectivity towards Ni(2+) over other metal ions under specific conditions. Upon addition of Ni(2+) to the modified AgNPls solution, a distinctive color change can be clearly observed by naked eyes as a result of the aggregation of AgNPls induced by the binding between Ni(2+) and the modified ligands. To verify a complete self-assembly of the GSH and Cys onto AgNPls surface, the modified AgNPls were characterized using Fourier transform infrared spectroscopy (FTIR), ultraviolet-visible spectroscopy (UV-vis) and transmission electron microscopy (TEM), respectively. Moreover, various parameters affecting the Ni(2+) quantification including the modifier ratio, pH, reaction time, and interferences were investigated. With UV-vis spectrophotometric measurement under optimal conditions, a quantitative linearity was established in the range of 10-150 ppb (R(2)=0.9971) with the detection limit of 7.02 ppb or 120 nM (S/N=3). In addition, the developed sensor was applied to the determination of Ni(2+) in waste samples from a jewelry factory and a car manufacturer with satisfactory results. Overall, this alternative approach presents a simple, rapid, sensitive and selective detection of Ni(2+).

Reverse-phase liquid chromatographic determination of α-lipoic acid in dietary supplements using a boron-doped diamond electrode.

A development of ultra-high performance liquid chromatographic coupled with a novel inkjet-printed conductive ink-modified electrode for a fast and simultaneous determination of polyphenolic antioxidants was achieved. Two printing techniques were selected for fabrication and modification including (i) an in-house screen-printing method and (ii) an inkjet-printing method, respectively. A conductive ink containing graphene and polyaniline nanocomposite (G-PANI) was precisely casted onto the surface of screen-printed carbon electrode (SPCE) using a dimatix inkjet material printer. Compared to a bare SPCE, the G-PANI-modified screen-printed carbon electrode (G-PANI/SPCE) exhibited higher electrochemical sensitivity with increase (2-4 times) of peak current of each antioxidant. Moreover, four antioxidants were successfully separated and determined within 3 min using a reverse phase ultra-high performance liquid chromatography (UHPLC) with a mobile phase containing phosphate buffer and acetonitrile (90:10 v/v). Under an optimal detection potential at +1.2V vs. Ag/AgCl, linear calibrations and limits of detection (S/N=3) for antioxidants were found to be 0.01-10 µg mL(-1) and 1.38-1.94 ng mL(-1), respectively. Finally, this proposed method has been successfully used for the determination of antioxidants in tea samples, the results obtained from our presented method were within a highly good agreement those obtained from a standard UHPLC-UV method.

Electrochemical droplet-based microfluidics using chip-based carbon paste electrodes for high-throughput analysis in pharmaceutical applications.

A fast liquid chromatographic separation, coupled with sensitive and straightforward detection using a boron-doped diamond (BDD) electrode, was developed and validated for the determination of α-lipoic acid in dietary supplement samples. The analysis was carried out using a reversed phase C18 (150 mm × 4.6 mm, 5 μm) column with a mobile phase consisting of a 1:1 (v/v) ratio of 0.05 M phosphate solution (pH 2.5):acetonitrile, at a flow rate of 1.0 mL/min. The detection potential obtained from hydrodynamic voltammetry was 1.05 V vs. Ag/AgCl. Under optimized conditions, the chromatographic separation was performed in less than 5 min, a good linear relationship was obtained between the current and the α-lipoic concentration within the range of 0.01-60 μg/mL (correlation coefficient of 0.9971), and a detection limit of 3.0 ng/mL was determined. Furthermore, this method was successfully applied to determine α-lipoic acid concentrations in selected commercial dietary supplement samples. The recovery of α-lipoic acid in spiked samples at 0.5, 5.0 and 30 μg/mL ranged from 94.4% to 103.6% with a relative standard deviation (RSD) of between 1.2% and 3.7%. In real samples, this developed methodology produced results that were highly correlated with the standard HPLC-UV approach. Therefore, the present method can be used for fast, selective and sensitive quantification of α-lipoic acid in dietary supplements.

Simple and rapid determination of ferulic acid levels in food and cosmetic samples using paper-based platforms.

This paper presents the first example of a pharmaceutical application of droplet-based microfluidics coupled with chronoamperometric detection using chip-based carbon paste electrodes (CPEs) for determination of dopamine (DA) and ascorbic acid (AA). Droplets were generated using an oil flow rate of 1.80 μL min(-1), whereas a flow rate of 0.80 μL min(-1) was applied to the aqueous phase, which resulted in a water fraction of 0.31. The optimum applied potential for chronoamperometric measurements in droplets was found to be 150 mV. Highly reproducible analysis of DA and AA was achieved with relative standard deviations of less than 5% for both intra-day and inter-day measurements. The limit of detection (LOD) and limit of quantitation (LOQ) were found to be 20 and 70 μM for DA and 41 and 137 μM for AA, respectively. Linearity of this method was in the ranges of 0.02-3.0mM for DA and 0.04-3.0mM for AA. This system was successfully applied to determine the amounts of DA and AA in intravenous drugs. Calibration curves of DA and AA for quantitative analysis were obtained with good linearity with R(2) values of 0.9984 and 0.9988, respectively. Compared with the labeled amounts, the measured concentrations of DA and AA obtained from this system were insignificantly different, with error percentages of less than ±3.0%, indicating a high accuracy of the developed method.