Modeling of SAM Impedance Onto Gold and Silver Thin-Film Mass-Produced Electrodes and Their Use for Optimization of Lactic Acid Detection

In this work, we demonstrate how an innovative, out-of-cleanroom customized CD/DVD fabrication process can be successfully used for mass production of biosensors with thin-film electrodes. We show that silver and gold electrodes can be used for impedimetric and voltammetric biosensing applications, both in presence and absence of a redox mediator. We modeled the redox/non-redox electrodes impedance through equivalent electrical circuits, and we evaluated their transfer function sensitivity with a one-factor-at-a-time approach. Using this approach, we introduced a new prediction method to find which equivalent electrical circuit elements contribute more to the transfer function variations, then we experimentally validated the predictions measuring the electrodes electrochemical impedance spectroscopy responses with relevant self-assembled monolayer molecules immobilized on them, i.e., MCH and DTSP. We also assess the silver electrodes long-term stability with impedance spectroscopy measurements over a period of 1200 hours, proving their possible use in point-of-care applications. Finally, we also prove that the sensors correctly perform in a practical case, i.e., as a lactic acid biosensor, by studying the optimization of the biosensor efficiency through different enzyme immobilization methods. By comparing lactate oxidase enzyme direct adsorption and covalent binding to DTSP self-assembling monolayers, we found that covalent binding to DTSP can boost the catalytic current of about 40% with respect to that obtained from the direct adsorption of the same enzyme concentration.