The aim of this work is the realization of a nanostructured platform for the rapid and selective determination of the FKBP12 protein in biological fluids, i.e., CSF and blood. FKBP12 is a peptidyl-prolyl cis-trans isomerase with a clear role both in neurodegenerative processes and in the anti-rejection response after surgical transplantation. The sensor platform is built on a QCM support on which plasmonic silver nanoparticles (AgNPs) are assembled. Self-assembled monolayers (SAMs) containing the GPS-SH1 receptor, specifically designed and synthesized to bind FKBP12, were prepared on the nanostructures using different anti-fouling molecular spacers.
The plasmonic nanostructures were obtained by electrodeposition and have manifold functions: increasing the sensitivity of QCM measurements as well as of creating a plasmonic coating for SERS and SPR applications. Exploring different experimental conditions for the electrodeposition, we prepared two different types of AgNPs: flower-like nanostructures and dendritic nanostructures. The AgNPs were characterized by means of UV-Vis and reflection spectroscopy, SEM, QCM, and contact angle. The body of the results showed that the preparation of the nanostructures was reproducible and provided homogeneous coating of the surface with the AgNP.
The SERS performance of the plasmonic nanoarchitectures was studied using Rhodamine 6G as the analyte, and the measurements revealed low detection limits for both nanostructures, indicating that the Ag dendrites are the most promising platform for the SERS-based nanosensor. QCM measurements have shown that the dendritic nanostructures functionalized with SAM containing GPS-SH1 allowed the detection of the FKPB12 protein at picomolar concentrations. Furthermore, it has been demonstrated that two proteins, i.e., BSA and IgG, present in the biological fluids of interest, do not interfere with the determination of FKBP12 when used at their physiological concentrations. Finally, it was found that the addition of ethanol, following the absorption of FKBP12 and/or interferents, allows the sensor to be fully regenerated.
