Modern researches and also the laboratories increasingly need the methods to measure the small volumes as microliter of analytical samples for determination of various analytes with a high accuracy. An electrochemical biosensor based on a modified carbon paste electrode with hydrogel as an absorbent polymeric matrix and banana as a source of polyphenol oxidase was constructed and it was used for determination the concentration of paracetamol in one microliter volume of solution. The electrochemical oxidation of paracetamol was studied by cyclic voltammetry and square wave voltammetry. The effective parameters on the voltammetric response of the constructed biosensor were optimized. The results obtained by cyclic voltammetry revealed that the banana-hydrogel carbon paste electrode shows a higher current response compared to a banana carbon paste electrode and hydrogel carbon paste electrode. Because of high absorption property of hydrogel, the proposed electrode has the capability to measure only one μL of sample solution, which is very important and considerable property for limited volumes of sample solutions. The modified electrode also exhibits a low detection limit (1.6 picomole) with a good linear range (10–250 picomole) and it has a good reproducibility and stability in both basic and acidic environments even in the presence of the enzyme and a long life time (20 days) for measurement of paracetamol in solutions.

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