A sensitive fluorescent probe based on dithizone-capped ZnS quantum dots for quercetin determination in biological samples

Enhanced electrochemical determination of quercetin in a choline chloride-based ionic liquid

Electrochemical techniques have been applied to determine quercetin and to evaluate its antioxidant effect. Deep eutectic solvents as a new generation of green solvents are promising electrolyte catalytically active additives for electrochemical oxidation of quercetin. Herein, in this work, Au was directly electrodeposited on the surface of graphene-modified glassy carbon electrodes, and AuNPs/GR/GC electrodes were fabricated. Choline chloride-based ionic liquids as deep eutectic solvents were readily prepared and applied to detect quercetin in buffer solutions, allowing a detection enhancement. X-ray diffraction and scanning electron microscopy were carried out to characterize the morphology of AuNPs/GR/GCE. Fourier transform infrared spectroscopy was carried out to interpret the H-bond interactions between the DES and quercetin. This electrochemical sensor exhibited good analytical performance. The low detection limit was reduced to 0.5 μM in a 15% DES solution, which was 300% higher than the signal without DES. It proved to be fast and environmentally friendly for the determination of quercetin and the DES had no effect on antioxidant effects of quercetin. In addition, it has been successfully applied in real sample analysis.

Highly photoluminescent nitrogen-doped carbon quantum dots as a green fluorescence probe for determination of myricetin

Highly photoluminescent N-doped carbon quantum dots (N-CDs) which the quantum yield reached 63% were prepared through hydrothermal treatment. The obtained N-CDs displayed a uniform distribution of particle size, superior stability in high-salt conditions, and excellent sensitivity. A green fluorescence probe based on N-CDs was constructed for ultrasensitive determination of myricetin in vine tea on account of the static quenching. The N-CDs presented excellent linear fluorescence response in the concentration range of 0.2-40 μM and 56-112 μM and with a low detection limit of 56 nM. Additionally, the practicability of the probe was verified in spiked vine tea sample, and the satisfactory recoveries of myricetin varied from 98.8% to 101.2%, with relative standard deviations in the range of 1.52%-3.48%. It is the first time to employ N-CDs without any material modification as a fluorescence sensor to detect myricetin, which is a promising approach to expand the path for myricetin screening.

Electrochemical determination of quercetin using glassy carbon electrode modified with WS2/GdCoO3 nanocomposite

A WS₂/GdCoO₃ nanocomposite was successfully prepared using hydrothermal-assisted synthesis. Our prepared WS₂/GdCoO₃ nanocomposite was fabricated on a glassy carbon electrode (GCE) for the detection of quercetin (QCT). The WS₂/GdCoO₃ nanomaterial was characterized by powder XRD, micro-Raman, FT-IR, XPS, FE-SEM, and HR-TEM, which proved that WS₂ nanoplates were finely dispersed on the surface of the GdCoO₃ nanoflakes. The electrocatalytic performance of WS₂/GdCoO₃ was investigated by the EIS technique, and it exhibited a small semi-circle, which confirms that it has a large active surface area and high electrical conductivity. The electrochemical behavior of QCT at the WS₂/GdCoO₃ sensor was explored by using the CV and DPV methods. The proposed electrochemical sensor exhibited excellent electrochemical response toward QCT with a wide linear range of 0.001 to 329 µM, low limit of detection (LOD) of 0.003 µM, and limit of quantification (LOQ) of 0.0101 µM. The sensor also displayed excellent selectivity, sensitivity, reproducibility, and stability. Additionally, the WS₂/GdCoO₃ sensor was utilized for the detection of QCT in apple juice and grape juice samples, and it exhibited good recovery results.