Optical characterization of a nanogel–nanostar plasmonic nanocomposite for microfluidic sensing and surface-enhanced Raman scattering

Abstract

Plasmonic nanoparticles embedded in polymer matrices combine the exceptional optical properties of plasmonic nanoparticles with the versatile mechanical and chemical characteristics of polymers, enabling robust and functional surface-enhanced Raman scattering (SERS) detection platforms for chemical sensing. SERS has become one of the most powerful analytical techniques due to the electromagnetic and chemical enhancement of plasmonic nanoparticles, realizing enhancement factors up to 12 orders of magnitude. In particular, gold nanostars are highly efficient and sensitive SERS facilitators due to the extreme near-field enhancement that arises from their sharp tips and branches, commonly referred to as ‘hotspots’. Self-assembling phospholipid nanogels that exhibit thermally reversible pseudoimmobilization properties offer a unique opportunity for designing biocompatible plasmonic nanocomposites with thermally responsive viscosity profiles. Hence, a thermally responsive plasmonic nanocomposite was designed by embedding gold nanostars in a phospholipid nanogel. Remarkably, this nanogel–nanostar composite can be reversibly immobilized in microfluidic channels for SERS analysis and then flushed out of the channel for reuse of the microchannel. The optical properties of gold nanostars were analyzed to characterize the reliability and sensitivity of the nanogel–nanostar composite for SERS sensing and detection applications. Finally, the nanogel–nanostar composite was applied to SERS analysis in a microfluidic device, demonstrating a low nanomolar detection performance for rose bengal dye.