Preparation Of Thiazole Polymer Film Modified Electrode And Its Application In Biological Analysis

Dopamine(DA) is one of the important catecholamine neurotransmitters in the mammalian central nervous system, and it is widely applied to the treatment of circulatory collapse syndrome caused by the myocardial infarction, trauma, endotoxin sepsis, cardiac surgery or congestive cardiac failure. Uric acid(UA), a primary end product of purine metabolism, its abnormal level is commonly a symptom of some diseases, like hyperpiesia, leukemia and pneumonia. Xanthine(XN) is a purine nucleotide catabolism of intermediates, and will be converted to uric acid in the role of xanthine oxidase. XN levels in plasma and urine concentrations can be used as a sensitive indicator of some pathological conditions, especially for xanthine aciduria. Nitrite(NO2-), a precursor to carcinogenic nitrosamines, is important within environmental, food and physiological systems, and its excessive level in blood will result in haemoglobin oxidation. Moreover, it could enhance or inhibit the release of DA. It is nearly impossible to determine DA, UA, XN and NO2- selectively or simultaneously at bare electrodes due to the weak and overlapped oxidation waves and the electrode fouling caused by the adsorption of their oxidation products, which can lead to the poor sensitivity and selectivity. Hence, the development of sensitive and selective biosensors for their selective or simultaneous detection is highly desirable for analytical applications and also diagnostic researches.To solve these problems, various modified electrodes have been constructed and used to selectively or simultaneously determine DA, UA, XN and NO2-. Conjugated polymers always have irreplaceable position in the electrochemical academic circles due to their numerous advantages, such as strong selective, good stability, high repeatability, and the thickness of the electrode surface can be controlled. Recently, thiazole-based polymers also gradually got people’s attention due to their unexceptionable selectivity and sensitivity. This paper includes three aspects as followed:1. A Poly(2,6-diamino-4,5,6,7-tetrahydrobenzothiazole)(PDTBT) modified glassy carbon electrode(GCE)(PDTBT/GCE) had been fabricated by electropolymerization of DTBT and used for the simultaneous detection of DA and UA in 0.1 mol L-1 phosphate buffer solution(PBS, p H 7.0). The results were showed that the PDTBT modified GCE not only exhibited excellent electrocatalytic activity toward the electrooxidations of DA and UA, but also resolved the weak and overlapped voltammetric responses of DA and UA into two sensitive and well-defined oxidation peaks with a large peak potential separation of 0.14 V, which can be applied for the selective and simultaneous determinations of DA and UA in a mixture. Under the optimum conditions, the anodic peak currents of DA and UA were linearly dependent on the concentrations of DA and UA in the ranges of 0.1–100 and 2.0–1000 μmol L-1 with the correlation coefficients of 0.9984 and 0.9990, respectively. The detection limits were 0.05 μmol L-1 and 0.20 μmol L-1(S/N=3). In 0.1 mol L-1 PBS p H 7.0, the PDTBT film exhibited good electrochemical activity, showing a surface-controlled electrode process with the apparent heterogeneous electron transfer rate constant(ks) of 25.9 s-1 and the charge–transfer coefficient(α) of 0.49, and thus displayed the features of an electrocatalyst.The practical use of the modified electrode had been used for the simultaneous detections of DA and UA in urine samples by using standard adding method with satisfactory results.2. A thiazole-based copolymer(PABT-DMSA) had been synthesized by electrochemical copolymerization of 2-aminobenzothiazole(ABT) and 2,3-dimercaptosuccinic acid(DMSA) on glassy carbon electrode(GCE), and it was used for the simultaneous detection of DA and UA. The performance of the PABT-DMSA/GCE towards the electrooxidation of DA, UA and XN had been investigated by CV and DPV methods. The results displayed that the modi?ed electrode not only exhibited excellent electrocatalytic activity toward the electrooxidations of DA, UA and XN in PBS(p H 7.0), but also could separate the weak oxidation waves of these species at bare GCE into three well-defined and strong oxidation peaks. The peak potential separations are 120 m V for DA–UA and 410 m V for UA–NO2- using DPV, which are large enough for the simultaneous determinations of DA, UA and XN. The linear concentration dependences of the DPV responses for DA, UA and XN are in the ranges of 0.1~360 μmol L-1,0.4~800 μmol L-1,0.8~1500 μmol L-1 with correlation coefficients of 0.9965, 0.9959 and 0.9965, respectively. The detection limits are 0.01 μmol L-1, 0.02 μmol L-1 and 0.07 μmol L-1 for DA, UA and XN, respectively(S/N=3). The modified electrode had been used for the simultaneous determinations of DA, UA and XN in human urine and serum samples by using standard adding method with satisfactory results.3. Poly(5-mercapto-1H-tetrazole-1-acetic acid)(PMTAA) film modified glassy carbon electrode(GCE) has been fabricated and used for selective and simultaneous detections of DA, UA and NO2- in 0.1 mol L-1 PBS(p H 6.0). The poly(5-mercapto-1H-tetrazole-1-acetic acid) film(PMTAA) modified GCE(PMTAA/ GCE) not only exhibits electro-catalytic effects towards the oxidations of DA, UA and NO2- with negatively shifted oxidation potentials and enhanced peak current responses, but also resolves the weak and overlapped voltammetric responses of DA, UA and NO2- into three strong and well-de?ned voltammetric peaks with both CV and DPV echniques, which can be employed for the selective and simultaneous determinations of DA, UA and NO2- in their mixture. Under the optimum conditions, the linear concentration dependences of the DPV current responses are observed for DA, UA and NO2- in the concentration ranges of 0.2~110 μmol L-1,1~600 μmol L-1 and 8~1100 μmol L-1, with the correlation coefficients of 0.9945, 0.9932 and 0.9944, respectively. The detection limits are 0.03 μmol L-1, 0.2 μmol L-1 and 0.5 μmol L-1 for DA, UA and NO2-, respectively(S/N=3). The practical application of the modified electrode has been investigated by the simultaneous determinations of DA, UA and NO2- in human urine samples by using standard adding method with satisfactory results.