Transistor Amplifier as an Electrochemical Transducer with Intuitive Optical Read-out: Improving Its Performance with Simple Electronic Solutions

Highlights: • A simple device for transduction of electrolytic (analytical) current to a visual perception was designed and optimised. • Functional aspects of the transducing element were discussed. • The performance of different amplifying elements and circuits was tested. • The price of the whole transducing system reached <0.3 € even at small-scale (experimental) production. - Abstract: A platform for electrochemical transduction suitable for miniaturised point-of-care diagnostic solutions with intuitive optical read-out was designed. Electrolytic current from electrochemical cell was transduced into the glow of a light-emitting diode. Its performance was optimised and several variants of transducing circuitry were tested. The circuit comprising field-effect transistor (FET) exhibited the sought abilities − absolute simplicity and high and tuneable sensitivity of the transducing device. Limit-of-detection, i.e. a signal readable by naked-eye without any additional instrumentation was as low as 4 μM for direct assay of H₂O₂. The whole transducing system employing FET consisted of 4 off-the-shelf components and its price reached <0.3 € even at small-scale experimental production. As our system was rather suitable for the semiquantitative "YES/NO" applications due to the steep response curve, an alternative circuitry for widening the linear range was also probed. Finally, rather higher initial voltage that was required in the electrochemical cell for FET-based transducer lead us to design a further simplified and more variable circuit employing the operational amplifier.