Study Of Quercetin And Rutin Modified Electrochemical Biosensors

Molecular structure, physical and chemical characters of quercetin and rutin, pharmacological effects and modifications of poly-film chemically modified electrode were summarized together with some coexisting substances in physiological system such as uric acid (UA) and the neuronal monoamines such as epinephrine (EP) and serotonin (5-HT) in this article. Based on the previous studies, the flavonoids molecules of quercetin and rutin were selected as modifier materials firstly and two late-model biosensor, Qu/WGE and Ru/WGE were prepared successfully by electrochemical method. The performance of modification resultant, morphology and their electrochemical activity were tested by the field emission scanning electron microscope (FE-SEM), infrared spectra (IR), in situ UY-spectroelectrochemical and electrochemical techniques. The admixture system of UA and AA, EP, 5-HT and AA had been analyzed using the electrochemical modified electrodes based on quercetin and rutin, respectively. Compared with the bare WGE, Qu/WGE shows excellent electrocatalytic effect towards the oxidation of both UA and AA. Ru/WGE displayed strong catalytic function for the oxidation of adrenalin (EP), serotonin (5-HT), and ascorbic acid (AA).For Qu modified on WGE, an optimized modification can be obtained. The results indicated that when the concentration of Qu is 0.5 mmol L^-1, pH of phosphate-buffered saline (PBS) is 7.0, the scan rate is 20 mV s^-1, the scan range is - 0.2 - 1.0 V, and the number of potential cycling is 4 cycles, the modification layer is optimum. Electrochemical measurements including cyclic voltammetry and electrochemical impedance spectrum techniques proved that the deposition film is electronegative and possessed electrochemical activity. The electrodeposition mechanism of Qu on WGE was analysed. Qu was oxidized companying two electrodes and two protons, 3', 4'-OH in ring B turned into o-quinone and had the ability of absorbing electron which made position 6'-C take positive charges partially, thus the anodically formed oxo-group can enter into a reaction with active functional groups existing at the surface of anodized carbon electrodes which act as nucleophiles with quinone rings. Through differential pulse voltammetry technique, the modified electrode was usd for determination of the admixture system of UA and AA. The result indicated that the electrode was sensitive to detect of UA selectively in presence of 500 times concentration of AA.A linear relation between the peak current and concentration was obtained for UA in the range of 1.0 - 50μM with a detection limit 1.0μM (r²= 0.995) with a separation peak potential of 280 mV. The modified electrode was used for determination of real urine sample and gained the ideal result. The experiment of the influence of pH for phosphate-buffered saline on UA and AA oxidation peak potential was done and the results showed that after UA and AA were oxidized via a two electron two proton process, UA produce allantoin by a hydrolyzation reaction, and for AA its electrochemical oxidation generates the dehydroascorbic acid (DAA).When prepared Ru/WGE modified electrode, through comparation of FE-SEM figure of deposition film by chronoamperometry and cyclic voltammetry technique, we concluded that the modified film by cyclic voltammetry was more regular, so in this article the modified electrode was fabricated by cyclic voltammetry. By some verification experiments of deposition film, the mechanism of Ru oxidation and polymerization was proposed. The o-OH in ring B of Ru molecule was oxidized and then produced phenoxy radicals that can interact eachother or with another Ru monomer to give rise to a strongly adherent film and deposited on the surface of the electrode companying the Ru molecules embeded and adsorbed in the film. These Ru molecules can stably exist in the polyfilm and probably keep the excellent electrochemical activity. The Ru/WGE was used to detect physiological activity molecules and got satisfying result. Compared with bare WGE, Ru/WGE displayed strong catalytic function for the oxidation of adrenalin (EP), serotonin (5-HT), and ascorbic acid (AA) by increasing the oxidation currents which shows the effective electrode surface was enlarged and resolved the overlap voltammetric response of EP and AA into two well-defined voltammetric peaks of about 172 mV and that of 5-HT and AA about 288 mV, respectively. A linear response in the range of 3.0 -90.0μM with the detection limit of 8.0×10^-7 M for EP was obtained in coexistence of AA (0.01 mM). The relationship between the peak current and concentration of AA and 5-HT were 2.0 - 60.0μM with the detection limit of 1.0μM and 0.3 - 9.0μM with the detection limit of 0.1μM respectively, together with a separation peak potential of 288 mV.The reaction mechanism of 5-HT, EP and AA on the Ru/WGE were analysed. The three substances' oxidation potential moved negatively with the increase of pH, and the slope of liner relationship indicated that their oxidation reaction followed a two electron two proton process.The modified electrodes showed high stability, reproducibility and anti-fouling ability. For Qu/WGE, during the first 3 days the signal showed 3% decrease, in the 7 days the current response decreased by about 5% of its initial response and in the following 1 months by 10%. For Ru/WGE, during the first 3days the signal showed a 5% decrease; in the 7 day, the current response decreased by about 8% of its initial response and in the following month by 15%. So the electrodes are promising for the physiological study and clinical diagnosis.