Dopamine (DA) and other catecholamines play important roles in the functioning of the central nervous system, cardiovascular, renal and hormonal systems as well as in drug addiction and Parkinson disease. Therefore, it is essential to develop simple and rapid methods for determination these biological molecules in routine analysis. The development of voltammetric sensors for the determination of neurotransmitters, uric and ascorbic acids human fluid such as urine and serum has received considerable interest in recent years. A sol-gel carbon composite electrode (CCE) has been prepared by mixing a sol-gel precursor (eg. Methyirimethoxysilane) and carbon powder without adding any electron transfer mediator or specific reagents. It is demonstrated that this sensor can be used for simultaneous determination ascorbic acid, neurotransmitters (dopamine and adrenaline) and uric acid. Direct electrochemical oxidation of ascorbic acid, uric acid and catecholamines at a carbon composite electrode is investigated. The experimental results were compared with other common carbon based electrodes, specifically, boron doped diamond, glassy carbon, graphite and carbon paste electrodes. It is found that the CCE shows a significantly higher of reversibility for dopamine. In addition, in comparison to other electrodes used for CCE the oxidation peaks of uric acid, ascorbic acid and catecholamines in cyclic and square wave voltammetry were well resolved at the low positive potential with good sensitivity. The advantages of this sensor are high sensitivity, inherent stability and simplicity and ability for simultaneous determination of uric acid, catecholamines and ascorbic acid without using any chromatography or separation systems. The analytical performance of this sensor has been evaluated for detection of biological molecules in urine and serum as real samples.
