# Thickness-Tunable PDMS-Based SERS Sensing Substrates

## TL;DR

This paper introduces a method to create flexible, ultra-thin SERS substrates using PDMS and D5, enabling sensitive molecular detection.

## Contribution

A tunable thickness PDMS-based SERS substrate is developed using D5 dilution and spin-coating for flexible sensing.

## Key findings

- PDMS-D5 mixtures enabled film thickness control down to 100 nm via spin-coating.
- Ag nanoparticles formed on PDMS surfaces achieved SERS detection limits as low as 0.1 ppm for R6G.
- The method uses PDMS’s Si-H bonds to reduce Ag+ ions into uniformly bonded AgNPs.

## Abstract

Surface-enhanced Raman scattering (SERS) spectroscopy is an ultra-sensitive analytical method with the powerful signal-molecule detection capability. Coupling with the polydimethylsiloxane (PDMS) material, SERS can be enabled on a polymeric substrate for fast-developing bio-compatible sensing applications. However, due to PDMS’s high viscosity, conventional PDMS-SERS substrates are typically thick and stiff, limiting their freedom for engineering flexible micro/nano functioning devices. To address this issue, we propose to adopt a low viscosity decamethylcyclopentasiloxane (D5) solvent as a diluent solution. Via controlling the mixture ratio of D5 and PDMS and the spin-coating speed for deposition, this method resulted in a film of a well-defined thickness from sub-millimeter down to a 100 nm scale. Furthermore, thanks to the unsaturated Si-H chemical bonds in the PDMS curing agent, the PDMS film could effectively reduce the Ag+ ions to Ag nanoparticles (NPs) directly bonding onto the substrate surface uniformly. Via adjusting the size and density of the AgNPs through reaction temperature and time, strong SERS was achieved and verified using R6G with the detection limit down to 0.1 ppm, attributed to the AgNPs’ plasmonic enhancement effect.