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Different tyrosinase carbon paste modified electrodes to determine bisphenol A (BPA) concentration in aqueous solutions have been constructed. Variables examined were in the carbon paste composition and in particular: (i) the immobilized enzyme amount; (ii) the carbon type (powder, single or multi-walled nanotubes); (iii) the nature of the pasting oil (mineral oil, hexadecane and dodecane). For each biosensor type the amperometric response was evaluated with reference to the linear range and sensitivity. Constant reference has been made to the amperometric signals obtained, under the same experimental conditions, towards the catechol, a specific phenolic substrate for tyrosinase. The most efficient biosensors were those constructed by using the following composition for the carbon paste: 10% of tyrosinase, 45% of single wall carbon nanotubes (SWCN) and 45% of mineral oil. This biosensor formulation displayed the following electrochemical characteristics: a sensitivity equal to 138 microA/mM, LOD of 0.02 microM (based on three times the S/N ratio), linear range of 0.1-12 microM and response time of 6 min. This experimental work represents a first attempt at construction of a new carbon nanotube-tyrosinase based biosensor able to determine the concentration of BPA, one of the most ubiquitous and hazardous endocrine disruptors which can pollute the drinking and surface water, as well as many products of the food chain.

The results obtained with a glucose biosensor operating under non-isothermal conditions are presented and discussed. Glucose oxidase, immobilized onto Nylon membranes, was used as biological element. An amperometric two electrodes system was employed to measure the anodic current produced by oxidation of hydrogen peroxide. Non-isothermal conditions were characterised in terms of the temperature difference, delta T = Tw - Tc, and of the average temperature of the system, Tav = (Tw + Tc)/2, Tw and Tc being the temperature in the warm and cold half-cells constituting the biosensor. Comparison between the functioning of the biosensor under isothermal and non-isothermal conditions was performed. It was found that, under non-isothermal conditions, the dynamic response and sensitivity increased, while the response times and the detection limit decreased, if comparison was done with the same parameters measured under isothermal conditions. The increase of the dynamic response was found to be proportional to the applied temperature gradient.