Construction And Application Of Flavonoids Electrochemical Sensors

Flavonoids show pharmacological activities,including antioxidant,anti-inflammatory,antibacterial,antitumor,cardioprotection,neuroprotection,immune regulation,antispasmodic,expectorant,and other aspects.They exist widely in daily diet and related drugs,which is of great significance in anti-aging,disease prevention and treatment.Therefore,for using flavonoids effectively and exerting their health benefits,it is important to analyze the accurate contents of flavonoids.Electrochemical analysis allows a fast response,low consumption,and competitive sensitivity,and it exhibits more advantages over traditional techniques.In this thesis,taking quercetin and luteolin as the analytical targets,we constructed several new electrochemical sensors based on various functionalized nanomaterials and different modification technique,and established new analytical methods for flavonoids by optimizing the experiment conditions.We also explored their applications in food and drug analysis.The main research contents are as follows:(1)A nitrogen-doped graphene-ionic liquid-glassy carbon microsphere paste electrode(N-GE/GCILE)was constructed for the ultra-sensitive determination of quercetin(Qu).The N-GE with typically crumpled and folded morphologies exhibited large specific surface area,which could increase the effective area of the modified electrode and provide plentiful active sites for Qu.The ionic liquid was also an excellent conductive mediator.Therefore,the N-GE/GCILE exhibited enhanced electrochemical response towards Qu compared to unmodified glassy carbon microsphere paste electrode.The influencing conditions on sensitivity such as theamount of modifier,accumulation potential and time,and electrolyte pH value were respectively discussed.Under the optimized experiment conditions,peak current of Qu was linear with the concentration of Qu within the ranges of 0.002-0.1 μM and 0.1-10 μM.The method provided wide linear ranges,low detection limit(1 nM),good reproducibility,stability,and high selectivity.The fabricated electrode was successfully applied for Qu detection in blueberry juice with satisfactory results,which confirmed the feasibility of N-GE/GCILE for the determination of Qu in food samples.(2)Electropolymerization is one of the popular modification methods in the electrochemistry field.The obtained polymer film by this technique shows high stability and electrical conductivity,and its thickness can be controlled by scanning cycles.Hence,we introduced electropolymerization of methylene blue(MB)in the construction of poly(methyleneblue)/copper nanowires modified electrode(PMB/CuNWs@nano-CPE)for high-performance luteolin sensing.Cyclic voltammetry(CV)and square wave voltammetry(SWV)were utilized to investigate the electrochemical behaviors of luteolin on the fabricated electrodes.In comparison with unmodified carbon paste electrodes,the PMB/CuNWs@nano-CPE presented better electrocatalytic activity towards luteolin with enhanced oxidation peak current.Under optimal conditions,the calibration plots obtained by SWV were linear in two ranges of 0.5 nM to 0.01 μM and 0.01 μM to 1 μM,with a low detection limit(LOD)of 0.1 nM(S/N=3).The sensor could be used for selective determination of luteolin with outstanding anti-interference ability;the method has been successfully applied for luteolin analysis in Chinese medicine capsule samples.