Point-of-Care Tests via Pollen-Based Nanoplasmonic Chips Combined with a Synthetic Receptor for FKBP12 Biomarker Detection at a Single-Molecule Level.

The selective and rapid detection of FKBP12 is crucial due to its involvement in immunosuppression, neurodegenerative and oncological diseases, and some fundamental cellular processes. A low-cost point-of-care test (POCT) based on a simple setup, combined with plasmonic sensor chips for ultrasensitive detection of FKBP12, is developed. The sensing principle exploits pollen-based natural nanostructures covered by gold nanofilms and functionalized with synthetic GPS-SH1 receptors. The experimental results demonstrated ultrahigh performance due to the hybrid plasmonic phenomena, with a detection limit of 0.17 aM for FKBP12. This label-free optical-chemical sensor is based on portable and simple equipment, operates in 10 min, requires a small volume of the sample, and only requires a dilution step to perform the measurement on real samples. The high selectivity of the developed sensor chip for FKBP12 is demonstrated, and its applicability in complex matrices such as serum and plasma is validated. Furthermore, two surface functionalization strategies with different receptor-to-spacer ratios, 1:6 and 1:3, are investigated, identifying the optimal ratio to achieve better binding sensitivity. This work highlights the potential of plasmonic nanostructured pollen-based chips functionalized with GPS-SH1 receptors for the detection of FKBP12 at the single-molecule level, paving the way for advances in diagnostics and therapeutic monitoring via low-cost POCT with cheaper and disposable chips.