A dual-mode assay kit using a portable potentiostat connected to a smartphone via Bluetooth communication and a potential-power angle-based paper device susceptible for low-cost point-of-care testing of iodide and dopamine.

BACKGROUND: Considering that the brain controls most of the body's activities, it is very important to measure the factors affecting its function, such as dopamine and iodide. Due to the growing population in the world, it is necessary to provide fast, cheap and accurate methods with the capability of on-site analysis and without the need for invasive sampling and operator skill. As a result, there is a strong desire to replace laboratory instruments with small sensors for point-of-care testing. Paper-based analytical devices (PADs) are one of the popular zero-cost approaches to achieve this goal. RESULTS: We developed a simple and disposable diagnostic paper system based on electroanalytical and potential-power angle-based methods. First, we prepared an angle-based analytical system capable of performing semi-quantitative iodide analysis simply by reading the colored angle traveled. This system design is based on a channel containing complex reagents and two pencil-drawn electrodes to apply a constant voltage accelerating the anions migration. Meanwhile, a three-electrode system based on conductive pencil graphite is developed to measure dopamine concentration based on linear sweep voltammetry. For the quantitative analysis, the voltammetric data was wirelessly transmitted to a mobile device via Bluetooth communication. In this context, a power supply providing the required voltage for the migration of iodide ions, a portable potentiostat system, and a mobile application for measuring dopamine were developed. The calibration curves for I- and dopamine range from 3.5 × 10-4-47.0 × 10-4 and 10.0 × 10-6-1000.0 × 10-6 mol L-1 with LODs of 2.3 × 10-4 and 5.0 × 10-6 mol L-1, respectively. SIGNIFICANCE AND NOVELTY: A new portable dual-mode voltage-assisted integrated PAD platform was designed for iodide and dopamine analysis. The characteristics of this device allow non-experts to carry out in-field analysis using sub-100 µL saliva sample with a time-to-result of <10 min along with reducing the overall cost and operational complexity.

A new approach of magnetic field application in miniaturized pipette-tip extraction for trace analysis of four synthetic hormones in breast milk samples.

Herein, a novel homemade electrical device was designed, including two pieces of external neodymium magnets, providing a reciprocating magnetic field to introduce a magnetic-assisted dispersive pipette-tip micro solid-phase extraction. To evaluate the performance efficiency of the proposed method, a novel magnetic calcined GO/SiO2@Co-Fe nanocube sorbent was synthesized, filled into the pipette-tip, exposed to the reciprocating magnetic field, and applied for the preconcentration of some hormone therapy drugs in human biological matrices. The effective adsorption and desorption parameters were optimized using a rotatable central composite design and one-variable-at-a-time approaches. Under the optimized conditions, the target analytes' detection limits were found to be below 0.02 ng mL-1. Moreover, the calibration curves were linear in the range of 0.03-500.00 ng mL-1 (R2 > 0.9966), with RSDs% less than 7.8 %. Eventually, the established method was applied to extract the analytes from breast milk samples, followed by LC-ESI-MS/MS analysis.

Electrochemically deposition of ionic liquid modified graphene oxide for circulated headspace in-tube solid phase microextraction of naphthalene from honey samples followed by on-line liquid chromatography analysis.

In this work, an inexpensive, fast, and selective ionic liquid modified graphene oxide (GO-IL) was synthesized and electrochemically deposited on the inner surface of a stainless-steel tube. Then, it was applied for circulated headspace in-tube solid-phase microextraction (CHS-IT-SPME) of naphthalene from honey samples. Next, the coated tube was replaced with the sample loop of a six-port injection valve for on-line desorption and further HPLC-UV analysis of naphthalene. The sorbent was characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), Fourier-transform infrared spectroscopy (FT-IR), and energy-dispersive X-ray spectroscopy (EDX). Different parameters affecting the procedure efficiency, including extraction temperature, extraction time, salt concentration, and sample volume were optimized by central composite design and response surface methodology. Under the optimum conditions, the calibration curve was linear within the range of 0.3-200 ng mL-1, with a regression coefficient of 0.9972. The limits of detection (LOD) and quantification (LOQ) were found to be 0.1 ng mL-1 and 0.3 ng mL-1, respectively. Intra-day and inter-day RSDs% for three replicate measurements of naphthalene at the concentration of 10 ng mL-1 were obtained 3.9% and 5.0%, respectively. Also, good tube-to-tube reproducibility of 5.3% was achieved. Finally, the method was successfully applied for measuring trace amounts of naphthalene in honey samples. Relative recoveries were calculated within the range of 90.0-106.5%, indicating excellent efficiency of the proposed method.

In-tube stir bar sorptive extraction based on 3-aminopropyl triethoxysilane surface-modified Ce-doped ZnAl layered double hydroxide thin film for determination of nonsteroidal anti-inflammatory drugs in saliva samples.

A thin-film based on 3-aminopropyl triethoxysilane surface-modified Ce-doped zinc-aluminum layered double hydroxide was synthesized on the inner surface of an aluminum tube. It has been applied to in-tube stir bar sorptive extraction of nonsteroidal anti-inflammatory drugs in saliva samples followed by high-performance liquid chromatography. The sorbent was characterized by scanning electron microscopy, X-ray diffraction, Fourier-transform infrared spectroscopy, energy-dispersive X-ray spectroscopy, and elemental mapping. The extraction parameters including sample pH (4.2), extraction time (10 min), stirring speed (800 rpm), type of eluent (acidified tetrahydrofuran), eluent volume (100 µL), and desorption time (6 min) were thoroughly optimized. Under the optimum conditions, limits of detection were found to be less than 5.0 ng mL-1. Calibration plots were linear within the range 10-1000 ng mL-1 (R2 > 0.9982). Absolute recoveries were calculated in the range 63.5 to 72.4%. The repeatability (intra- and inter-day precision) and reproducibility (tube-to-tube precision) at concentrations of 50, 250, and 500 ng mL-1 were less than 7.6% and 9.4%, respectively. The method accuracy based on the relative error was calculated at these concentrations and ranged from - 4.9 to - 9.3% for intra-day relative error (%) and - 6.8 to - 11% for inter-day relative error (%). Finally, the method applicability was examined for the determination of nonsteroidal anti-inflammatory drugs in saliva samples, and good relative recoveries were obtained within the range 86.5 to 95.2%. As a result, the introduced method can be applied as a suitable alternative to measuring nonsteroidal anti-inflammatory drugs in biological fluids. Graphical abstract A surface-modified Ce-doped ZnAl LDH thin film was synthesized on the inner surface of an Al tube and applied for in-tube stir bar sorptive extraction of NSAIDs in saliva.