Comparative silane surface functionalization strategies for enhanced Bloch surface wave biosensing of anti-SARS-CoV-2 antibodies.

Surface functionalization plays a decisive role in the performance of biosensors, as it governs the efficiency and stability of biomolecule immobilization at the sensor interface and, consequently, the overall performance of the biosensing platforms. In this work, we present a comparative study of three organosilane chemistries - APTES, APDMS, and CPTES - applied to a SiO2-terminated 1D photonic crystal able to sustain Bloch surface waves and designed to operate as optical biosensors in both label-free and fluorescence-enhanced modes. Each chemistry was evaluated through a standardized label-free protocol based on the interaction between immobilized SARS-CoV-2 spike protein and its corresponding antibodies, enabling quantitative assessment of binding efficiency, nonspecific adsorption, and signal repeatability. CPTES exhibited the most favorable balance between specific signals, reduced variability, and low nonspecific adsorption. The three chemistries were subsequently tested in fluorescence mode for the detection of anti-SARS-CoV-2 IgG antibodies in human serum, demonstrating the suitability of BSW-enhanced fluorescence for rapid serological analysis. Overall, the study identifies CPTES as the most robust and reproducible functionalization strategy among the three investigated for BSW biosensing and highlights the potential of the platform for fast, sensitive detection of clinically relevant antibodies.