A regenerative biosensing surface in microfluidics using electrochemical desorption of short-chain self-assembled monolayer

We report a novel method to regenerate a biosensor surface in microfluidics. By applying a low DC voltage (0.9 V) between two electrodes submerged in phosphate buffered saline, the sensing surface resets to be reusable and reconfigurable; streptavidin-bound COOH-SAM completely desorbs and CH₃-terminated self-assembled monolayer (SAM) forms on the sensing surface to capture the subsequent target molecule, fibrinogen, in a microfluidic device. The biomolecular interactions are monitored by surface plasmon resonance in real time, and ellipsometry and linear sweep voltammetry are used to evaluate the results. Despite much study on the theoretical mechanism of electrochemical SAM desorption, relatively little research has been carried out on its full integration into a microfluidic system. This is because of electrode peeling-off and electrolysis occurring at a similar potential to the potential of the SAM desorption. In this paper, we report that the potential for the reductive desorption of thiol SAMs depends on the length of the alkyl chin, the type of terminal groups and the binding of proteins and that our approach using short-chain SAMs (n < 3) can be a good candidate to minimize these limitations. While the surface modified by proteins on the long-chain SAMs (n > 10) needs more than 1.0 V between two electrodes to be completely regenerated, the protein-bound surface on the short-chain SAMs (n < 3) does around 0.9-DC voltage. Linear sweep voltammetry demonstrates that hydrogen evolution (approx. -1.2 V) does not overlap the short-chain SAM desorption and the electrode does not peel off during the desorption process as well. It is shown that the modified proteins in the same microfluidic device are still stable even after 10 cycles showing a relative standard deviation lower than 1.86%.