ABSTRACT
A gold nanoparticle/graphene quantum dots (AuNP/GQD) nanozyme-modified screen-printed carbon electrode (SPCE) was developed for fast and ultrasensitive determination of quercetin by square-wave voltammetry. The nanosensing device was inserted in miniaturized equipment. Under the optimal experimental conditions, a good linear relationship between oxidation peak current and concentration of quercetin within a very wide range of 1.0 × 10-10 to 1.0 × 10-3 mol L-1 was obtained, with a very low limit of detection of 3.3 × 10-11 mol L-1. To prove the performance of the method, the reproducibility was evaluated and the RSD values were lower than 5.3% and 5.1% for the intra-day and inter-day measurements, respectively. The method was applied to the sensitive determination of quercetin in human plasma droplets with recovery rates of 92.6 to 101.7%.Graphical abstract.
Subject(s)
Electrochemical Techniques/methods , Metal Nanoparticles/chemistry , Quantum Dots/chemistry , Quercetin/blood , Carbon/chemistry , Catalysis , Electrochemical Techniques/instrumentation , Electrodes , Gold/chemistry , Graphite/chemistry , Humans , Limit of Detection , Oxidation-Reduction , Quercetin/chemistry , Reproducibility of ResultsABSTRACT
AIM AND OBJECTIVE: Melatonin is an essential biomarker for sleep-related disorders. Reliable methods of analysis are needed for melatonin. Therefore, a new chromophore (Rhodamine B) was proposed for the assay of melatonin; this method succeeded to enlarge the working concentration range and to decrease the limit of determination comparing with the method that just used the native fluorescence of melatonin. MATERIALS AND METHODS: Rhodamine B was proposed as a new chromophore for the assay of melatonin in biological, food, and pharmaceutical samples. Fluorescence was used for the determination of melatonin. RESULTS: The results obtained using Rhodamine B were compared with those obtained by the native fluorescence of melatonin. Using the new chromophore, melatonin was determined in the concentration range between 0.01 and 50 pmol L-1, with the detection limit of 2.4 fmol L-1. The recovery of melatonin was higher than 98.00% with a relative standard deviation of less than 0.10%, when the method was applied for the assay of melatonin in samples such as breast milk, whole blood, milk powder, and pharmaceutical formulations. CONCLUSION: Utilization of Rhodamine B enlarged the linear concentration range for the assay of melatonin and decreased the detection limit, making possible the assay of melatonin in a variety of samples such as pharmaceuticals, food, and biological samples.
