Acetylcholine is a neurotransmitter, which is located at the intersections of the nerve and muscles in the lymph nodes of the internal organs motor systems and in various parts of the central nervous system. A decrease of acetylcholine in brain is associated with Alzheimer‘s disease. That is why it is an important agent for this disease. In this study, a bienzymatic biosensor system with acetylcholine esterase and choline oxidase was prepared with carbon paste electrode modified with carbon nano Dot‐(3‐Aminopropyl) triethoxysilane (CDs‐APTES) for determination of the amount of acetylcholine. Acetylcholine esterase and choline oxidase enzymes were immobilized onto a modified carbon paste electrode by cross‐linking with glutaraldehyde. Determination of acetylcholine was carried out by the oxidation of enzymatically produced H2O2 at 0.4 V versus Ag/AgCl. The effect of temperature, pH, and substrate concentration on the acetylcholine response of the prepared biosensor was investigated. In addition, the optimum CDs‐APTES amount, the linear operating range of the biosensor, and the interference effect were also investigated.

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Dopamine (DA) is an important electroactive neurotransmitter. The concentration of DA in the body of a healthy person is approximately 1.0x10-7-1.0x10-3 M. A decrease in dopamine concentration is associated with Parkinson’s disease. Thus, it is important to determine the amount of dopamine in early diagnosis of Parkinson’s disease. Different methods such as immunoassay, flow injection analysis (FIA), high performance liquid chromatography (HPLC) etc. could be used for determination of dopamine but they are expensive and have long determination times, and pre analytic processes. In this study, a tyrosinase based amperometric biosensor was developed with carbon paste electrode modified with carbon nano dot 3-Chloropropyl-trimethoxysilane (CDs-CPTMS) for determination of the amount of dopamine. CDs-CPTMS was synthesized for the first time. Determination of dopamine was carried out by the reduction of dopamine-o-quinone at -0.15 V versus Ag/AgCl. The effect of temperature, pH, and substrate concentration on the dopamine response of the prepared biosensor and interference effect were investigated. There was no interference effect of uric acid and ascorbic acid. The designed biosensor has wide working range (0.001- 0.01μM and 0.01- 0.1 μM), low limit of detection, very good reproducibility and shelf life. In addition, the preparation of the biosensor is practical and cost-effective.

Bisphenol-A (BPA) is a monomer commonly used in the production of epoxy resins, plastic bottles and dental filling materials. Due to its chemical structure, BPA and its derivates shows activity similar to the endocrine hormones. It can bind to estrogen receptors and cause neurological disturbances, even at low doses. Therefore, it is important to determine BPA and its derivatives quickly and sensitively at low concentrations. In this study, a single amperometric tyrosinase enzyme biosensor was designed for the determination of the amount of BPA, BPF (Bisphenol F) and BPS (Bisphenol S) monomers. Tyrosinase was immobilized onto a modified carbon paste electrode by cross-linking with glutaraldehyde. The amount of BPA (BPS and BPF) was determined directly on the reduction of quinone compound that released as a result of the enzymatic reaction at -0.15V. Km(app) value of the designed biosensor for BPA was found 0.00067 ?M, the linear operating range was 0.001-0.005 ?M (a) and 0.03-0.1 ?M (b) and the lower detection limit was found 1 nM for each monomer. It is clear that designed biosensor is enable the fast, efficient and precise determination of BPA and its derivatives released from materials used in dental materials.

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