Study On Highly Sensitive Electrochemical Detection Of Flavonoids

Flavonoids is a kind of plant chemicals which mainly concentrated in plant fruits,seeds, flowers, bark and roots, etc. These materials have many biological activities,such as antibacterial property, anti-inflammatory, analgesic, anti-cancer, antioxidantactivity and so on. It is harmless to the human body at the same time. With theincreasing of the incidence of various diseases, flavonoids plays an increasinglysignificant role in the medical field. Electroanalytical chemistry has good selectivity,high sensitivity, easy operation and fast analysis speed. Different modified electrodescan be made according to the electrical activity of analyte, which greatly widen itsapplication. It has extensive development and application in the detection offlavonoids.In the present thesis, ionic liquid/multiwalled carbon nanotubes electrode(ILs/MWNTsE) and reduced graphene oxide/multi-walled carbon nanotubes/Aunanoparticles modified carbon fiber microdisk electrode (RGO/MWNTs/AuNPsME)was developed. And they were used to sensitively detect baicalin in scutellaria powderby the square wave voltammetry and astragalin, rutin and quercetinin in mulberryleaves by capillary electrophoresis with electrochemical detection (CE-ECD)respectively.In the first chapter, the development of flavonoids and electrochemical detectionwere reviewed. Several common materials which were usually used in chemicallymodified electrode, such as carbon nanotube, graphene metal nanopaticles and ionicliquids, were introduced. Finally, the development of flavonoids determined byelectrochemical detection was simply presented.In the second chapter, baicalin, a kind of flavonoids, extracted from the dry rootof radix scutellariae, plays an important role in biochemical reaction in vivo, such asanti-aids, anti-inflammatory, sedative, anti-cancer, radical scavenging and antioxidanteffects. A kind of composite electrode was fabricated using multiwall carbonnanotubes (MWNTs) and the ionic liquid1-dodecyl-3-methylimidazoliumhexafluorophosphate (DDMIMPF6). Cyclic voltammetry (CV) and square wave voltammetry (SWV) were used to investigate its catalytic and absorptive performancefor baicalin. It showed notable power to adsorb baicalin and resulted in a considerablesignals enhancement. The high adsorptive activity was contributed to the high specificsurface area and the specific surface characteristics of carbon nanotubes. The additionof ionic liquids facilitated the electron transfer between baicalin and electrodeeffectively. This method was selected to measure the content of baicalin in urinesample and radix scutellariae with high stability, high sensitivity and reproducibility.In the third chapter, astragalin, rutin and isoquercitrin have excellent properties,such as antibacterial, anti-inflammatory, anti-oxidation and so on. The threeflavonoids are common active ingredients in traditional Chinese medicine such asmulberry leaves, which are safe and non-toxic. They were widely applied in the fieldof pharmaceutical, clinic and cosmetic. The RGO/MWNTs/AuNPsME was fabricatedby electrodepositing AuNPs and dipping in GO/MWNTs complex solution and thenreduced by electrochemical method. SEM and CV were used to describe themorphology and performance of the RGO/MWNTs/AuNPsME. It showed excellentelectrocatalysis to the three flavonoids and resulted in a considerable signalsenhancement. The addition of AuNPs facilitated the electron transfer betweenelectrode and modified membrane effectively. The high signals enhancement wascontributed to the high specific surface area and the specific surface characteristics ofcarbon nanotubes. RGO was easily form a thin film, which enhanced the stability ofthe electrode surface. The RGO/MWNTs/AuNPsME was used as the detector incapillary electrophoresis with electrochemical detection and applied to analyzeastragalin, rutin and isoquercitrin in mulberry leaves simultaneously with satisfactoryresults. There were several merits of the novel electrochemical detector coupled withCE, such as comparative repeatability, easy fabrication and high sensitivity, hold greatpotential for the flavonoids assay.