Extending Surface‐Enhanced Raman Spectroscopy to Liquids Using Shell‐Isolated Plasmonic Superstructures

Abstract

Plasmonic superstructures (PS) based on Au/SiO2 were prepared for Shell‐Isolated Nanoparticle‐Enhanced Raman Spectroscopy (SHINERS) in liquid phase applications. These superstructures are composed of functionalized SiO2 spheres with plasmonic Au nanoparticles (NPs) on their surface. Functionalization was performed with (3‐aminopropyl)trimethoxysilane, (3‐mercaptopropyl)trimethoxysilane and poly(ethylene‐imine) (PEI). Of these three, PEI‐functionalized spheres showed the highest adsorption density of Au NPs in TEM, UV/Vis and dynamic light scattering (DLS) experiments. Upon decreasing the Au NP/SiO2 sphere size ratio, an increase in adsorption density was also observed. To optimize plasmonic activity, 61 nm Au NPs were adsorbed onto 900 nm SiO2‐PEI spheres and these PS were coated with an ultrathin layer (1–2 nm) of SiO2 to obtain Shell‐Isolated Plasmonic Superstructures (SHIPS), preventing direct contact between Au NPs and the liquid medium. Zeta potential measurements, TEM and SHINERS showed that SiO2 coating was successful. The detection limit for SHINERS using SHIPS and a 638 nm laser was around 10−12 m of Rhodamine (10−15 m for uncoated PS), all with acquisition settings suitable for catalysis applications.

Operando Nanoscale Sensors in Catalysis: All Eyes on Catalyst Particles

“…(d) Au and Au@SiO 2 can be assembled on larger SiO 2 spheres to form shell-isolated superstructures (SHIPS) for colloidally stable SHINERS experiments in liquids to observe Rhodamine 6G dye molecules up to picomolar quantities . Adapted with permission from ref . Copyright 2019 John Wiley and Sons.…”

“…Real-time measurements would require colloidally stable, plasmonic nanostructures with intrinsic hot spots that arise from sharp edges or from clustering the metal nanoparticles into shell-isolated plasmonic superstructures (SHIPS, Figure 2d). 42 Such structures would be useful in electrochemical experiments for online monitoring of the reaction products in solution, which would give complementary information to the surface-bound intermediate species, measured with SHINERS, on electrocatalyst monolayers, for which small amounts of products and low signals are expected (Figure 2e). In order to use SHINERS as a quantitative analysis tool for product analysis, controlled substrates with internal standards for SHINERS are required.…”