A novel and portable electrochemical sensor for 5-hydroxymethylfurfural detection using silver microdendrite electrodeposited paper-based electrode.

A portable paper-based electrochemical sensor has been developed to determine 5-hydroxymethylfurfural (5-HMF). A screen-printed carbon electrode (SPCE) was facilely fabricated for the first time on poster paper which showed a very satisfactory electrochemical response. The analytical performance of the electrode was enhanced by electrochemical deposition of silver microdendrites (AgMDs). The cathodic peak of 5-HMF occurred at approximately -1.48 V, lower than that obtained from the bare poster-SPCE. Moreover, the modified electrode showed a higher current response than the bare electrode, revealing that the AgMDs not only exhibited highlighted electrocatalytic features but also improved the electrical conductivity and increased the electrode surface area. Afterward, some influencing conditions were optimized, including scan rate and the number of scan cycles for AgMD deposition, pH, temperature, and square wave voltammetric parameters. Under the optimal conditions, the analytical characteristics of the proposed sensor were evaluated. The cathodic peak current increased linearly according to 5-HMF concentration over the range of 3-100 ppm, and the detection limit was 1.0 ppm. This low-cost, disposable electrochemical sensor provided environmentally friendly, simple and rapid detection, acceptable precision, good stability, and high selectivity. Additionally, this method can be applied to quantify 5-HMF in honey samples with satisfying accuracy.

A simple label-free electrochemical sensor for sensitive detection of alpha-fetoprotein based on specific aptamer immobilized platinum nanoparticles/carboxylated-graphene oxide.

A label-free electrochemical aptamer-based sensor has been fabricated for alpha-fetoprotein (AFP) detection. Platinum nanoparticles on carboxylated-graphene oxide (PtNPs/GO-COOH) modified screen-printed graphene-carbon paste electrode (SPGE) was utilized as an immobilization platform, and the AFP aptamer was employed as a bio-recognition element. The synthesized GO-COOH helps to increase the surface area and amounts of the immobilized aptamer. Subsequently, PtNPs are decorated on GO-COOH to enhance electrical conductivity and an oxidation current of the hydroquinone electrochemical probe. The aptamer selectively interacts with AFP, causing a decrease in the peak current of the hydroquinone because the binding biomolecules on the electrode surface hinder the electron transfer of the redox probe. Effects of aptamer concentration and AFP incubation time were studied, and the current changes of the redox probe before and after AFP binding were investigated by square wave voltammetry. The developed aptasensor provides a linear range from 3.0-30 ng mL-1 with a detection limit of 1.22 ng mL-1. Moreover, the aptamer immobilized electrode offers high selectivity to AFP molecules, good stability, and sensitive determination of AFP in human serum samples with high recoveries.

A novel flow injection amperometric sensor based on carbon black and graphene oxide modified screen-printed carbon electrode for highly sensitive determination of uric acid.

A simple, rapid, and cost-effective flow injection amperometric (FI-Amp) sensor for sensitive determination of uric acid (UA) was developed based on a new combination of carbon black (CB) and graphene oxide (GO) modified screen-printed carbon electrode (SPCE). The CB-GO nanocomposites were simply synthesized and modified on the working electrode surface to increase electrode conductivity and enhance the sensitivity of UA determination via the electrocatalytic activity toward UA oxidation. The morphologies and electrochemical properties of the synthesized nanomaterials were investigated through scanning electron microscopy (SEM), transmission electron microscopy (TEM), electrochemical impedance spectroscopy (EIS), and cyclic voltammetry (CV). The modified electrode was incorporated with FI-Amp to improve UA detection's sensitivity, stability, and automation. Some parameters affecting sensitivity were optimized, including pH of the electrolyte solution, applied potential, amount of CB-GO suspension, flow rate, injection volume, and reaction coil length. Using an applied potential of +0.35 V (vs Ag/AgCl), the anodic current was linearly proportional to UA concentration over the range of 0.05-2000 µM with a detection limit of 0.01 µM (3 S/N). Besides, the developed method provides a sample throughput of 25 injections h-1, excellent sensitivity (0.0191 µA/µM), selectivity, repeatability (RSD 3.1%, n = 7), and stability (RSD 1.08%, n = 50). The proposed system can tolerate potential interferences commonly found in human urine. Furthermore, a good correlation coefficient between the results obtained from the FI-Amp sensor and a hospital laboratory implies that the proposed system is accurate and can be utilized for UA detection in urine samples.

Non-Enzymatic Amperometric Glucose Sensor Based on Carbon Nanodots and Copper Oxide Nanocomposites Electrode.

In this research work, a non-enzymatic amperometric sensor for the determination of glucose was designed based on carbon nanodots (C-dots) and copper oxide (CuO) nanocomposites (CuO-C-dots). The CuO-C-dots nanocomposites were modified on the surface of a screen-printed carbon electrode (SPCE) to increase the sensitivity and selectivity of the glucose sensor. The as-synthesized materials were further analyzed for physico-chemical properties through characterization tools such as transmission electron microscopy (TEM) and Fourier-transform infrared spectroscopy (FTIR); and their electrochemical performance was also studied. The SPCE modified with CuO-C-dots possess desirable electrocatalytic properties for glucose oxidation in alkaline solutions. Moreover, the proposed sensing platform exhibited a linear range of 0.5 to 2 and 2 to 5 mM for glucose detection with high sensitivity (110 and 63.3 µA mM-1cm-2), and good selectivity and stability; and could potentially serve as an effective alternative method of glucose detection.

Flow injection amperometric sensor with a carbon nanotube modified screen printed electrode for determination of hydroquinone.

Flow injection amperometric (FI-Amp) sensor was developed for sensitive and selective determination of hydroquinone. A simple screen printed carbon electrode (SPCE) was modified with various nanomaterials for improvement of sensitivity on the determination of quinone. As a result, the appropriate sensitivity is obtained from the SPCE modified with carbon nanotube (CNT) which indicated that CNT contributed to the transfer of electron to quinone. The reproducibility (n=9) and repeatability (n=111) of SPCE-CNT were obtained at 4.4% and 3.6%RSD, respectively. The SPCE-CNT electrode and enzymatic column were incorporated to the FI-Amp system to determine hydroquinone. Laccase was immobilized on silica gel using a cross-linking method by glutaraldehyde modification and then packed in the column. The laccase column has high efficiency for catalytic oxidation of hydroquinone to quinone, which further detects by amperometric detection. Parameters affecting response of the proposed sensor, i.e., pH, ionic strength, and temperature have been optimized. The proposed system provided a wide linear range between 1 and 50 µM with detection limit of 0.1 µM. Satisfactory recoveries in the range of 91.2-103.8% were obtained for the analysis of water sample.