Biosensing with SiO2-covered SPR substrates in a commercial SPR-tool

• Stable SPR substrates were fabricated with standard evaporation techniques.
• Au substrates and SiO2-covered Au substrates were compared.
• Minimal experimental bulk sensitivity change with additional layers was observed.
• Experimental results were confirmed by theoretical simulations.
• Similar bio-assay results for both substrate types.

Surface Plasmon Resonance (SPR) is a well-established technique for studying binding kinetics and is extensively used in assay development as well as in drug discovery. Many biosensors contain an oxide surface instead of the conventional Au surface typically used in SPR sensing, which may introduce additional variables when using established protocols. Therefore, SiOx-covered SPR substrates are of great interest as a benchmarking tool for silicon-based biosensors. Moreover, SiOx has multiple advantages over Au, for instance with respect to the thermal stability of commonly used surface coupling strategies. In this paper, the bulk sensitivity of SiO2-covered Au substrates was evaluated for use in SPR. Both theoretical simulations and experimental results showed that the presence of ∼10 nm of SiO2 resulted in minimal loss of bulk sensitivity compared to Au substrates. This was proven for a prostate specific antigen (PSA) recognition immuno-assay. Thus we clearly demonstrated that SiO2-covered Au substrates can be used for biosensing applications and do not generate significant differences compared to the original Au substrates.