A hand-drawn graphite electrode for affordable analysis: Application to the enzymatic determination of tyramine in fish

The development of simpler and greener, but also reliable and efficient analytical sensors that meet the increasing global demands is a current challenge. In this work, a user-friendly and low-cost electrochemical cell was developed by combining two metallic wires (from a standard connector header) and a working electrode fabricated by pencil hand-drawing, which is one of the simplest, cheapest, and greenest ways of creating miniaturized electrodes. Graphite pencils with different degrees of hardness were tested and, using a 6B pencil, an electroanalytical platform with high precision (RSD < 5 %) was achieved. This platform was used as transducer for constructing an enzymatic biosensor for the determination of tyramine, using tyrosinase as the biological recognition element. After the optimization of several parameters, the biosensor showed a linear range between 5 and 150 mg<middle dot>L-1, a limit of detection of 0.4 mg<middle dot>L-1, and high selectivity for tyramine with no interference from other biogenic amines. This biosensor was successfully applied to the analysis of different fish species achieving recovery values between 87 % and 100 %. Its usefulness for monitoring tyramine concentration during the spoilage of a sardine sample was also demonstrated. Therefore, this cheap and miniaturized biosensor represents an interesting alternative for tyramine determination. Moreover, the good electrochemical features of the developed electrochemical cell demonstrated its potential for the development of future electrochemical sensors.