Preparation Of Purine Polymer Membrane And Its Application In Biological Analysis

Dopamine(DA), uric acid(UA), xanthine(XN), hypoxanthine(HXN) and ascorbic acid(AA) are usually coexisted in biological matrixes, and considered as the crucial molecules for some physiological processes in human metabolism. Due to their abnormal levels,it can cause several diseases, such as hypertension, leukemia, pneumonia, hyperuricaemia, and xanthinuria, etc. It is very important to detect the five biomolecules. However, the selective or simultaneous determinations of DA, UA, XN, HXN and AA at bare electrodes are nearly impossible because the oxidation potentials of AA, DA and UA are very close, and also, the oxidation products adsorbed on electrode surfaces can lead to poor sensitivity and selectivity.To overcome these obstacles, various materials have been used to modify the bare electrodes, such as grapheme, carbon nanotubes, metal nanoparticles, conductive polymers, etc. Due to simple preparation methods, strong selective, good stability, high repeatability, and the thickness of the electrode surface can be controlled, conductive polymers have aroused people’s concern, such as polythiophene, polythiazole, polyaniline, polypyrrole have received a great deal of interests. However, up to now, there is no study for electrochemical polymerization of purine-based and determination biomolecules by the purine-based polymers.This paper includes three aspects as followed:1. A poly(6-thioguanine-co-4-amino-3-hydrazino-5-mercapto-1,2,4-triazol)(P6-TG-AHMT) film modified glassy carbon electrode(GCE)(P6-TG-AHMT/GCE) has been fabricated by using electrochemical copolymerization of 6-thioguanine(6-TG) and 4-amino-3-hydrazino-5-mercapto-1,2,4-triazol(AHMT). The results show that the modified electrode not only exhibits strong electro-catalytic activities toward oxidations of DA and UA, but also can resolve the sluggish and overlapped voltammetric responses of DA and UA into two strong and well-defined oxidation peaks by using both CV and DPV, which can be applied for the selective and simultaneous determinations of DA and UA in a mixture. The P6-TG-AHMT/GCE exhibited high catalytic activities in 0.1 mol L-1 PBS p H 6.8. Under the optimum conditions, the linear dependences of DPV current responses are observed for DA and UA in the concentration ranges of 0.8~220 μmol L-1 and 1~2000 μmol L-1 with the correlation coefficients of 0.9987 and 0.9994, respectively. The detection limits are0.05 μmol L-1 and 0.06 μmol L-1 for DA and UA, respectively(S/N=3). Also, the P6-TG-AHMT/GCE showed good reproducibility and stabilities and wide concentration ranges. The application of P6-TG-AHMT/GCE is demonstrated by simultaneously determining the concentrations of DA and UA in human urine samples by using standard adding method with satisfactory results.2. A novel and simple electrochemical sensor based on the electro-polymerized film of 6-thioguanine(6-TG) modified on glassy carbon electrode(GCE) has been fabricated by using cyclic voltammetry(CV) techniques. The results show that the polymerized 6-TG modified GCE(P6-TG/GCE) not only exhibits electrocatalytic effects toward electrochemical oxidations of DA, UA, XN and HXN with negatively shifted oxidation potentials and enhanced peak current responses, but also can resolve the sluggish and overlapped voltammetric responses of DA, UA, XN and HXN into four strong and well-defined oxidation peaks by using both CV and DPV, which can be applied for the selective and simultaneous determinations of DA, UA, XN and HXN in a mixture. The P6-TG/GCE exhibited high catalytic activities in 0.1 mol L-1 PBS p H 7.0. Under the optimum conditions, the linear dependences of DPV current responses are observed for DA, UA, XN and HXN in the concentration ranges of 1–200 μmol L-1, 2–1600 μmol L-1, 1–500 μmol L-1 and 2–800 μmol L-1 with the correlation coefficients of 0.9986, 0.9997, 0.9997 and 0.9998, respectively. The detection limits are 0.05 μmol L-1, 0.06 μmol L-1, 0.30 μmol L-1 and 0.10 μmol L-1 for DA, UA, XN and HXN, respectively(S/N=3). Moreover, the P6-TG/GCE showed a rapid, simple, selective and sensitive protocol for simultaneous determinations of DA, UA, XN and HXN with wide concentration ranges and good reproducibility and stabilities. The application of P6-TG/GCE are demonstrated by simultaneously determining the concentrations of DA, UA, XN and HXN in human urine and serum samples by using standard adding method with satisfactory results.3. A poly(6-thioguanine-co-o-aminobenzene sulfonic acid)(P6-TG-ABSA) film modified glassy carbon electrode(GCE)(P6-TG-ABSA/GCE) has been fabricated by using electrochemical copolymerization of 6-thioguanine(TG) and o-aminobenzene sulfonic acid(ABSA). The surface morphology and electrochemical activity of the modified electrode has been investigated by using scanning electron microscope(SEM) and electrochemical methods. The SEM images show that the copolymer film exhibits a granular surface structure with regular and homogeneous particles,which is helpful to the electro-catalytic oxidations of the analytes. The results show that themodified electrode exhibits strong electro-catalytic activities toward oxidations of ascorbic acid(AA) and dopamine(DA) in 0.1 mol L-1 phosphate buffer solution(PBS,p H 5.0) by cyclic voltammetry(CV) and differential pulse voltammetry(DPV). Compared with those at P6-TG/GCE and PABSA/GCE,the current responses in anodic peak signal remarkably increase and the peak potential separation is 0.20 V at P6-TG-ABSA/GCE,which can be used for the simultaneous determinations of AA and DA in their mixture with high sensitivity. Under the optimum conditions,the linear dependences of DPV current responses are observed for AA and DA in the concentration ranges of 2-5000 μmol L-1 and 2-180 μmol L-1, with the correlation coefficients of 0.9996 and 0.9997,respectively. The detection limits are 0.06 μmol L-1,and 0.05 μmol L-1 for AA and DA, respectively(S/N=3). The different electrochemical behaviors of AA and DA at various scan rates indicate that the electrode reaction of AA is a diffusion-controlled process, and DA is an adsorption-controlled process at P6-TG-ABSA/GCE. The application of P6-TG-ABSA/GCE is demonstrated by simultaneous determinations of AA and DA concentrations in human urine samples with satisfactory results.As a result of various tests, the purine compounds 6-thioguanine has exhibited high catalytic activities towards dopamine, uric acid, xanthine, hypoxanthine and ascorbic acid. At the same time, the copolymer film exhibits more strong electro-catalytic activities, when the 6-thioguanine has been polymerized with aniline and thiazole-based substance. Therefore, the applications of purine compounds in the combination of the modified electrode and the catalytic activities of biomolecules are worthy of further study.