Electrodeposited NiO/graphene oxide nanocomposite: An enhanced voltammetric sensing platform for highly sensitive detection of uric acid, dopamine and ascorbic acid

Electrochemically Grown Hole-Rich NiO(OH) Thin Films toward Hole-Mediated Very Fast and Selective Enzyme-Free Electrochemical Sensing of Dopamine under Simulated Environment

This work aimed to develop an enzyme-free semiconductor-assisted electrochemical technique for the selective detection of the neurotransmitter dopamine. In this case, electrochemically grown nickel oxyhydroxide [NiO(OH)] thin films were chosen to fabricate the sensing platform, i.e., the electrodes. Chronoamperometry was used to deposit the films on indium tin oxide (ITO) coated glass substrates. The films were thoroughly characterized to establish their structure, composition, phase purity, and electrochemical attributes. Electrochemical sensing characteristics were investigated by means of cyclic and differential pulse voltammetry, steady-state amperometry, and electrochemical impedance spectroscopy. The effects of several interfering agents like glucose, sodium chloride, methanol, hydrogen peroxide, and paracetamol were also studied on the detection attributes of dopamine. Significantly high value of sensitivity (11.87 μA μM-1 cm-2) was obtained for dopamine sensing that was associated with a limit of detection (LoD) of 0.22 μM of dopamine. However, the sensitivity (2.51 μA μM-1 cm-2) and LoD (1.20 μM) obtained for serotonin were inferior compared to those of dopamine. The performance of the electrode toward dopamine sensing was not compromised either in the presence of only serotonin or a series of other electroactive interfering agents, which makes the electrode very much dopamine selective. The dopamine response time was 200 ms, which is notably fast. Extensive studies on the effect of temperature, pH and scan rate on the detection of dopamine by the developed electrode material have also been carried out. The developed electrodes were also found to be notably stable for dopamine detection with a decay of only 6.6% in oxidation peak current density after the 50th cycle. Real-life application of the developed electrode material was checked with urine samples from adult male humans and yielded encouraging results.

La(OH)3 Multi-Walled Carbon Nanotube/Carbon Paste-Based Sensing Approach for the Detection of Uric Acid—A Product of Environmentally Stressed Cells

This paper aims to develop an amperometric, non-enzymatic sensor for detecting and quantifying UA as an alert signal induced by allergens with protease activity in human cell lines (HEK293 and HeLa). Uric acid (UA) has been classified as a damage-associated molecular pattern (DAMP) molecule that serves a physiological purpose inside the cell, while outside the cell it can be an indicator of cell damage. Cell damage or stress can be caused by different health problems or by environmental irritants, such as allergens. We can act and prevent the events that generate stress by determining the extent to which cells are under stress. Amperometric calibration measurements were performed with a carbon paste electrode modified with La(OH)₃@MWCNT, at the potential of 0.3 V. The calibration curve was constructed in a linear operating range from 0.67 μM to 121 μM UA. The proposed sensor displayed good reproducibility with an RSD of 3.65% calculated for five subsequent measurements, and a low detection limit of 64.28 nM, determined using the 3 S/m method. Interference studies and the real sample analysis of allergen-treated cell lines proved that the proposed sensing platform possesses excellent sensitivity, reproducibility, and stability. Therefore, it can potentially be used to evaluate stress factors in medical research and clinical practice.

Construction of cationic polyfluorinated azobenzene/reduced graphene oxide for simultaneous determination of dopamine, uric acid and ascorbic acid

A highly sensitive cationic polyfluorinated azobenzene/reduced graphene oxide (C₃F₇-azo⁺/RGO) nanocomposite electrochemical sensor for simultaneous detection of dopamine (DA), ascorbic acid (AA) and uric acid (UA) was successfully synthesized using a facile exfoliation/restacking method. The nanocomposite is self-assembled from oppositely charged graphene oxide nanosheets (GO) and polyfluorinated azobenzene cations (C₃F₇-azo⁺), and then obtained by electrochemical reduction. The structure and electrochemical properties were characterized by X-ray diffraction (XRD), energy dispersive spectrometer analysis (EDS), transmission electron microscope (TEM) and scanning electron microscope (SEM). The electrochemical property of C₃F₇-azo⁺/RGO was characterized by cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), and differential pulse voltammetry (DPV). It can be clearly seen from experimental results that C₃F₇-azo⁺/RGO-modified electrode (C₃F₇-azo⁺/RGO/GCE) can detect DA, AA and UA simultaneously, and has good stability and anti-interference performance. The detection limits are 65 nM, 8 nM and 11 nM for DA, AA and UA in the ranges 57.28-134.28 μM, 0.04-6.01 μM, 9.23-23.45 μM, respectively.

Bi2S3/rGO Composite Based Electrochemical Sensor for Ascorbic Acid Detection

The engineering of an efficient electrochemical sensor based on a bismuth sulfide/reduced graphene oxide (Bi2S3/rGO) composite to detect ascorbic acid (AA) is reported. The Bi2S3 nanorods/rGO composite was synthesized using a facile hydrothermal method. By varying the amount of graphene oxide (GO) added to the synthesis, the morphology and size of Bi2S3 nanorods anchored on the surface of rGO can be tuned. Compared to a bare glassy carbon electrode (GCE), the GCE modified with Bi2S3/rGO composite presented enhanced electrochemical performance, which was attributed to the optimal electron transport between the rGO support and the loaded Bi2S3 as well as to an increase in the number of active catalytic sites. Cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) analysis of Bi2S3/rGO/GCE demonstrate that the active Bi2S3/rGO layer on GCE plays an important role in the electrochemical behavior of the sensor. In particular, the Bi2S3/rGO/GCE sensor shows a wide detecting range (5.0–1200 μM), low detection limit (2.9 µM), good sensitivity (268.8 μA mM−1 cm−2), and sufficient recovery values (97.1–101.6%) for the detection of ascorbic acid.

Electrochemical approach toward reduced graphene oxide-based electrodes for environmental applications: A review

Graphene has shown great potential in various application fields due to its excellent carrier transportation, ultra-high specific surface area, good mechanical properties, and light transmittance. However, pure graphene still exhibits some insurmountable defects, such as difficulty in simple and large-scale preparation, and limitations in application. The electrochemical method is a simple, clean, and environmentally friendly method. The rapid and simple preparation of graphene and its derivatives by electrochemical methods has important environmental significance. Moreover, rGO-based nanohybrids can be prepared by convenient and quick electrodeposition or cyclic voltammetry (CV), or to change the morphology and structure of graphene and its derivatives to achieve the purpose of improving material properties. This work mainly summarizes electrochemically related graphene from four aspects: (i) the method of electrochemical exfoliation of graphene; (ii) types of electrodeposition rGO-based nanohybrids; (iii) electrochemical regulation of the structure of rGO-based mixtures; (iv) environmental applications of rGO-based nanohybrids prepared by electrodeposition. This article critically discusses the advantages and disadvantages of electrochemical-related graphene, outlines future challenges, and provides insightful views and references for other researchers.

Electrostatic repulsion strategy for high-sensitive and selective determination of dopamine in the presence of uric acid and ascorbic acid

In this work, poly(sodium 4-styrenesulfonate)-functionalized three-dimensional graphene (PFSG) composites were realized via a facile and green strategy. The nanocomposite was characterized by scanning electron microscopy, ultraviolet and visible spectroscopy, X-ray photoelectron spectroscopy, and electrochemical method. An electroanalytical sensor of dopamine (DA) with high sensitivity and selectivity was fabricated based on PFSG modified glassy carbon electrode (GCE). Under the optimum conditions, the negatively charged PFSG composites exhibit strong electrostatic attraction for DA and electrostatic repulsion to the negatively charged ascorbic acid (AA) and uric acid (UA) molecules. Such electrostatic interaction hindered the enrichment of AA and UA on the surface of PSFG/GCE, which make a higher selectivity for the DA even in the presence of 120-fold AA and UA. Owing to the enhanced electron transfer rate and the stronger surface attraction, the current signal of DA on PFSG/GCE was about 160 times enhanced compared with the bare electrode. There was a good linear relationship between the reduction peak current of DA and concentration across the range of 0.002-2.0 μmol L^-1 and 2.0-10.0 μmol L^-1 with the limit of 0.8 nmol L^-1. Further, the PFSG/GCE was applied to the detection of DA in human serum samples. This biosensor is simple, sensitive, selective and highly stable, which provided a new design strategy and a valuable tool to detect DA in complex samples.