Low-Variance Surface-Enhanced Raman Spectroscopy Using Confined Gold Nanoparticles over Silicon Nanocones

Abstract

Surface-enhanced Raman spectroscopy (SERS) substrates are of utmost interest in the analyte detection of biological and chemical diagnostics. This is primarily due to the ability of SERS to sensitively measure analytes present in localized hot spots of the SERS nanostructures. In this work, we present the formation of 67 ± 6 nm diameter gold nanoparticles supported by vertically aligned shell-insulated silicon nanocones for ultralow variance SERS. The nanoparticles are obtained through discrete rotation glancing angle deposition of gold in an e-beam evaporating system. The morphology is assessed through focused ion beam tomography, energy-dispersive X-ray spectroscopy, and scanning electron microscopy. The optical properties are discussed and evaluated through reflectance measurements and finite-difference time-domain simulations. Lastly, the SERS activity is measured by benzenethiol functionalization and subsequent Raman spectroscopy in the surface scanning mode. We report a homogeneous analytical enhancement factor of 2.2 ± 0.1 × 10 7 (99% confidence interval for N = 400 grid spots) and made a comparison to other lithographically derived assemblies used in SERS. The strikingly low variance (4%) of our substrates facilitates its use for many potential SERS applications.

Alternative nano-lithographic tools for shell-isolated nanoparticle enhanced Raman spectroscopy substrates

“…Recent work showed that Au nanoparticles placed on vertically aligned silicon nanocones resulted in homogeneous enhancement factors with high orders of magnitude of ∼10 8 . 30 A high enhancement factor ensures good quality sensing capabilities of a SERS substrate. Lithographic structures also give rise to homogeneity in the measured SERS signal, providing uniform results over a large area.…”

“…In the comparative view reported in our previous work, we see that when lithographic techniques are used, SERS signal variance can be reduced to as low as 4%. 30 For SHINERS, an additional metal oxide layer must be applied on the enhancing nanostructures to use a lithographic substrate and make it applicable for a catalytic reaction. Therefore, in approach 2, a lithographically fabricated AuNP@SiNC geometry was employed.…”

“…2.2.1 Au nanoparticle on silicon nanocone fabrication. The Au nanoparticle on silicon nanocone (AuNP@SiNC) geometry was fabricated according to the methods described by Jonker et al 30 The SiNCs were fabricated using a combination of Displacement Talbot Lithography (EULITHA PhableR 100C) and reactive ion etching (OXFORD INSTRUMENTS PlasmaPro 100 Estrelas) The SiNCs are arranged in a square periodic lattice with a pitch of 250 nm. The deposition of 65 nm AuNP on the SiNC was performed using a discrete-rotation glancing angle deposition technique.…”