Microfluidic surface-enhanced raman scattering sensors for online monitoring trace chemical mixing and reaction

We report a microfluidic surface-enhanced Raman scattering (SERS) sensor for online monitoring the mixing and reaction between chemicals of low concentration. The SERS sensor is made up of a SERS-active substrate and a polydimethylsiloxane cap with microchannels for delivering solutions. The SERS substrate consists of noble-metal covered silicon nanopillar-forest patterns, which are fabricated based on an oxygen-plasma-treating-on-photoresist technique. Enhancement factor of the device is self-calibrated to be on the order of 5.2×10⁵, by utilizing the flat-metal areas beside the nanopillar-forest patterns as references. The mixing process of Crystal Violet and Rhodamine 6G trace solutions is characterized in the SERS sensor online and in real-time. Other kinetic features, including flow and diffusion, are also revealed.