Plasmonic nanostructures represent a suitable platform for the detection of biomolecules interaction. Their surface functionalization can be performed through different strategies such as polymer coating or solgel-based coverages. Optimal thickness, homogeneity and hydrophilicity of the functional layer can play a crucial role in defining the sensing capabilities that are required to perform bioassays.

In this framework, we combined two complementary approaches that improve the aforementioned features. First, the nanostructure surface was covered with a thin layer of Tetraethyl orthosilicate (TEOS) which improve the chemical homogeneity of the surface. Then a commercial polymer bearing biomolecule-active moieties (Lucidant MCP polymers) is coated on the TEOS layer. The polymer layer decreases the contact angle of the surface preventing the aggregation of biomolecules during immobilization.

The total thickness of the functionalized nanostructure was below 10 nm, ensuring the biomolecules to be placed in proximity of the sensing surface. In this way the functionalized nanostructure is compatible, at the same time, with both Surface Plasmon Resonance (SPR) and Plasmonic Enhanced Fluorescence (PEF) modality of detection.

In our more recent studies, we focused on PEF and surfaces optimized with the combined layer of TEOS and MCP polymer were evaluated in a commercial microarray scanner for protein assay. The fluorescence signal was collected and analyzed giving an effective improvement of the fluorescence intensity compared to a plasmonic nanostructure coated only with MCP polymer or a flat gold surface with the same combined TEOS and MCP coating.