A simple ultrasensitive electrochemical sensor for simultaneous determination of gallic acid and uric acid in human urine and fruit juices based on zirconia-choline chloride-gold nanoparticles-modified carbon paste electrode.

The determination of gallic acid (GA) and uric acid (UA) is essential due to their biological properties. Numerous methods have been reported for the analysis of GA and UA in various real samples. However, the development of a simple, rapid and practical sensor still remains a great challenge. Here, a carbon paste electrode (CPE) was modified by nanocomposite containing zirconia nanoparticles (ZrO2NPs), Choline chloride (ChCl) and gold nanoparticles (AuNPs) to construct ZrO2-ChCl-AuNPs/CPE as electrochemical sensor for the simultaneous electro-oxidation of GA and UA. Characterization was performed by Fourier transform infrared spectroscopy, X-ray diffraction, field emission scanning electron microscopy and energy dispersive X-ray spectroscopy. The modified electrode was investigated by different methods including electrochemical impedance spectroscopy and cyclic voltammetry. Kinetic parameters such as charge transfer coefficient, standard heterogeneous electron transfer rate constant and other parameters were calculated via voltammetry techniques. Differential pulse voltammetry was used for simultaneous determination of GA and UA applying the ZrO2-ChCl-AuNPs/CPE electrode. At the optimum conditions, this sensor showed a linear response in the ranges 0.22- 55 and 0.12-55 µM for GA and UA, respectively. In addition, low detection limits of 25 and 15 nM were obtained for GA and UA, respectively. Furthermore, ZrO2-ChCl-AuNPs/CPE was successfully applied for the independent determination of GA in green tea and fruit juice as well as the simultaneous determination of GA and UA in human urine samples.

Ultrasound-accelerated synthesis of gold nanoparticles modified choline chloride functionalized graphene oxide as a novel sensitive bioelectrochemical sensor: Optimized meloxicam detection using CCD-RSM design and application for human plasma sample.

In this research, gold nanoparticles modified choline chloride functionalized graphene oxide (AuNPs-ChCl-GO) was synthesized through the assistance of ultrasound and fabricated as a novel bioelectrochemical sensor and utilized for the sensitive detection of meloxicam (MEL). The morphological and structural features of the AuNPs-ChCl-GO were characterized using different techniques including FTIR, TEM, FE-SEM, EDX, and XRD. The modified electrode showed a remarkable improvement in the anodic oxidation activity of MEL due to the enhancement in the current response compared to the bare carbon paste electrode (CPE). The biosensor composition and measurement conditions were optimized using an experimental design. The differential pulse voltammetry (DPVs) exhibited expanded linear dynamic in the range of 9.0 × 10-9 to 8.5 × 10-7 M for MEL in Britton-Robinson buffer at pH = 4.0 with a detection limit of 1.008 × 10-9 M. The practical utility of the modified electrode was demonstrated by the accurate detection of MEL in human plasma sample.