Improved performance of aminopropylsilatrane over aminopropyltriethoxysilane as a linker for nanoparticle-based plasmon resonance sensors

Particle plasmon resonance (PPR) sensing is a powerful technique for label-free biosensing applications. Performance and sensitivity depend critically on careful attachment of gold nanoparticles (AuNPs) to the surface of a glass slide or optical fiber. We have developed a general and controlled strategy to bind AuNPs to glass slides or optical fibers using aminopropylsilatrane (APS) as a chemical linker, and compare the performance with the commonly used linker, 3-aminopropyltriethoxysilane (APTES). Test samples were characterized using a UV–Vis–NIR spectrophotometer and a fiber optic particle plasmon resonance (FOPPR) sensor system. The tested sensitivity using APS modified glass slides is 20.3% higher than that using APTES, and we attribute this to the relatively higher exposed AuNP surface area on APS. AFM topographical images showed that APTES surfaces exhibited a higher root mean square (RMS) roughness (∼130 pm) compared to APS (∼80 pm), and that AuNPs were embedded deeper in the APTES film. The contribution factor versus buried depth was modeled using the discrete dipole approximation method and results showed that sensitivity decreased with embedded depth. Although both APS and APTES showed comparable sensing performance, APS is easier to work with, allows faster processing time, is environmentally friendly, and leads to better reproducibility.