ACS applied materials & interfaces | 2019
Decoration of porous silicon with gold nanoparticles via layer-by-layer nano-assembly for interferometric and hybrid photonic/plasmonic (bio)sensing.
Abstract
Gold nanoparticle layers (AuNPLs) enable the coupling of morphological, optical and electrical properties of AuNPs in liquid dispersion with tailored and specific surface topography, making them exploitable in many bio-applications (e.g. biosensing, drug delivery, photothermal therapy). Herein, we report the formation of AuNPLs on porous silicon (PSi) interferometers and distributed Bragg reflectors (DBRs) for (bio)sensing applications via layer-by-layer (LbL) nano-assembling of a positively charged polyelectrolyte, namely polyallylamine hydrochloride (PAH), and negatively charged citrate-capped AuNPs. Decoration of PSi interferometers with AuNPLs enhances the Fabry-Perot fringe contrast due to increased surface reflectivity, resulting in an augmented sensitivity (roughly 100%) for both bulk and surface refractive index sensing using NaCl aqueous solutions to infiltrate the pores, in the former, and unspecific bovine serum albumin (BSA) adsorption on the pore surface, in the latter. Sensitivity enhancing is also confirmed for affinity and selective biosensing of streptavidin using a biotinylated polymer, namely, negatively-charged poly(methacrylic acid) (b-PMAA). Further, decoration of PSi DBR with AuNPLs envisages building up a hybrid photonic/plasmonic optical sensing platform. Indeed, both photonic (DBR stop-band) and plasmonic (localized surface plasmon resonance, LSPR) peaks of the hybrid structure are sensitive to changes of bulk refractive index (using 35% glucose aqueous solutions) and BSA unspecific adsorption. To the best of our knowledge, this is the first report about the formation of AuNPLs via LbL nano-assembly on PSi for i) the enhancing of the interferometric performance in (bio)sensing applications and ii) the building up of hybrid photonic/plasmonic platforms for sensing and perspective biosensing applications.