Glassy Carbon Electrode Modified with C/Au Nanostructured Materials for Simultaneous Determination of Hydroquinone and Catechol in Water Matrices

A Cu-functionalized MOF and multi-walled carbon nanotube composite modified electrode for the simultaneous determination of hydroquinone and catechol

Designing MOF-based materials with desired electrochemical activity and high electron conductivity may yield a novel electrochemical sensor that effectively detects various organic pollutants and conducts health monitoring. This study developed a facile and versatile electrochemical sensor for simultaneously monitoring the environmental pollutants hydroquinone (HQ) and catechol (CT). The electrodes are fabricated by modifying a GCE with a Cu-functionalized MOF (UiO-bpydc-Cu) and multi-walled carbon nanotubes (MWCNTs). The Cu-functionalized MOF effectively improved the electronic conductivity by metalating the 2,2'-bipyridyl-derived UiO-bpydc with Cu²⁺ ions. Moreover, due to the synergic effect, the composite electrode exhibits a significant voltammetric response to HQ's and CT's electro-redox. A rapid and sensitive method of synchronously detecting HQ and CT has been established by differential pulse voltammetry (DPV). The experiments reveal that the linear response ranges were 0.5-565 μM and 1-1350 μM for HQ and CT, respectively, with low detection limits of 0.361 μM and 0.245 μM. The proposed UiO-bpydc-Cu/MWCNTs/GCE electrochemical sensor shows high sensitivity, good anti-interference, reproducibility, and stability. It can also be applied for detecting HQ and CT in actual samples.

Electrochemical Detection of Dihydroxybenzene Isomers at a Pencil Graphite Based Electrode

In this work, an HB pencil electrode (HBPE) was electrochemically modified by amino acids (AAs) glycine (GLY) and aspartic acid (ASA) and designated as GLY-HB and ASA-HB electrodes. They were used in the detection of dihydroxybenzene isomers (DHBIs) such as hydroquinone (HQ), catechol (CC), and resorcinol (RS), by cyclic voltammetry (CV), and by differential pulse voltammetry. HBPE was characterized by scanning electron microscopy and energy-dispersive X-ray spectroscopy. These three electrodes showed a linear relationship of current with concentration of DHBIs, and the electrochemical processes were diffusion controlled in all cases. In simultaneous detection, the limit of detection, based on signal-to-noise ratio (S/N = 3), for HQ, CC, and RS was 12.473, 16.132, and 25.25 μM, respectively, at bare HBPE; 5.498, 7.119, and 14.794 μM, respectively, at GLY-HB; and 22.459, 25.478, and 38.303 μM, respectively, at ASA-HB. The sensitivity for HQ, CC, and RS was 470.481, 363.781, and 232.416 μA/mM/cm², respectively, at bare HBPE; 364.785, 282.712, and 135.560 μA/mM/cm², respectively, at GLY-HB; and 374.483, 330.108, and 219.574, respectively, at ASA-HB. The interference studies clarified the suitability and reliability of the electrodes for the detection of HQ, CC, and RS in an environmental system. Real sample analysis was done using tap water, and the proposed electrodes expressed recovery with high reproducibility. Meanwhile, these three electrodes have excellent sensitivity and selectivity, which can be used as a promising technique for the detection of DHBIs simultaneously.

Gold Nanoparticles/Carbon Nanotubes and Gold Nanoporous as Novel Electrochemical Platforms for L-Ascorbic Acid Detection: Comparative Performance and Application

Herein, the effects of nanostructured modifications of a gold electrode surface in the development of electrochemical sensors for L-ascorbic acid detection have been investigated. In particular, a bare gold electrode has been modified by electrodeposition of gold single-walled carbon nanotubes (Au/SWCNTs) and by the formation of a highly nanoporous gold (h-nPG) film. The procedure has been realized by sweeping the potential between +0.8 V and 0 V vs. Ag/AgCl for 25 scans in a suspension containing 5 mg/mL of SWCNTs in 10 mM HAuCl4 and 2.5 M NH4Cl solution for Au/SWCNTs modified gold electrode. A similar procedure was applied for a h-nPG electrode in a 10 mM HAuCl4 solution containing 2.5 M NH4Cl, followed by applying a fixed potential of −4 V vs. Ag/AgCl for 60 s. Cyclic voltammetry and electrochemical impedance spectroscopy were used to characterize the properties of the modified electrodes. The developed sensors showed strong electrocatalytic activity towards ascorbic acid oxidation with enhanced sensitivities of 1.7 × 10−2 μA μM−1cm−2 and 2.5 × 10−2 μA μM−1cm−2 for Au/SWCNTs and h-nPG modified electrode, respectively, compared to bare gold electrode (1.0 × 10−2 μA μM−1cm−2). The detection limits were estimated to be 3.1 and 1.8 μM, respectively. The h-nPG electrode was successfully used to determine ascorbic acid in human urine with no significant interference and with satisfactory recovery levels.

Glucose Biosensor Based on Dendritic Gold Nanostructures Electrodeposited on Graphite Electrode by Different Electrochemical Methods

In this research, we have demonstrated a one-step electrochemical deposition of dendritic gold nanostructures (DGNs) on a graphite rod (GR) electrode without any template, seeds, surfactants, or stabilizers. Three electrochemical methods, namely, constant potential amperometry (CPA), pulse amperometry, and differential pulse voltammetry, were used for DGN synthesis on GR electrode and further application in enzymatic glucose biosensors. Formed gold nanostructures, including DGNs, were characterized by a field emission scanning electron microscopy. The optimal concentration of HAuCl4 (6.0 mmol L−1), duration of DGNs synthesis (400 s), electrodeposition potential (−0.4 V), and the best electrochemical method (CPA) were determined experimentally. Then the enzyme, glucose oxidase, was adsorbed on the surface of DGNs and covalently cross-linked with glutaraldehyde vapor. The enzymatic glucose biosensor based on DGNs electrodeposited at optimal conditions and modified with glucose oxidase showed a quick response (less than 3 s), a high saturation current (291 μA), appropriate linear range (up to 9.97 mmol L−1 of glucose, R2 = 0.9994), good repeatability (RSD 2.4, 2.2 and 1.5% for 2, 30, 97 mmol L−1 of glucose), low limit of detection (0.059 mmol L−1, S/N = 3) and good stability. Additionally, this biosensor could be successfully applied for glucose determination in real samples with good accuracy. These results proved the principle of enzymatic glucose biosensor development based on DGNs as the basis for further investigations.