Tunable growth of gold nanostructures at a PDMS surface to obtain plasmon rulers with enhanced optical features

Abstract

Efficient coupling of plasmonic nanomaterials to optically transparent polymers still is a challenge in order to obtain affordable, versatile, and sensitive surface plasmonic devices. The in-situ fabrication of gold and silver nanoparticles on PDMS has been reported, but the resulting bulk sensitivities (of up to 70 nm RIU−1) may still be improved. The authors report that few simple modifications to the general preparation of these composites (AuNPs@PDMS) can result in substantial improvements of the optical features. A two-steps growth of AuNPs@PDMS is found to be particularly effective. It includes chemical treatment of the PDMS surface before the formation of well-exposed and densely-packed 3D conglomerates of gold spheroids with enhanced bulk sensitivity. Differently from available approaches, the structures obtained by this method display sensitivity to refractive index change of about 250 nm per RIU. This is 3.5 times higher than spherical nanoparticles prepared by similar protocols and is near the optical performance of anisotropic NPs. Due to the strong 3D character of the structures, excellent plasmon coupling is realized on PDMS surface. The authors also show that these nanocomposite substrates can be subjected to external stimuli and then exhibit red shifts or blue shifts typical of induced plasmon coupling and uncoupling. Hence, the method represents a major step forward in terms of high-performance composite plasmonic nanomaterials for use in biosensing.