Enabling spectral barcoding of SERS nanotags using gold nanostars

Abstract

Surface-enhanced Raman scattering (SERS) is a non-invasive analytical technique that has ultra-sensitivity and high multiplex capability. Owing to their sharp tips and corners, gold nanostars (AuNSs) with a unique near-infrared localised surface plasmon resonance have shown great potential in SERS and biomedical applications. In this study, we report the reproducible synthesis of AuNSs through a seedless, surfactant-free and green approach using 4-(2-hydroxyethyl)-1-piperazineethanesulfonic acid (HEPES). The localised surface plasmon resonance (LSPR) of AuNSs was tuned from 750 to 795 nm. AuNSs with a LSPR of 783 nm were selected to maximise the SERS performance because of the coupling resonance effect of the laser excitation wavelength (785 nm) with a LSPR peak of AuNSs. The SERS enhancement factor of AuNSs with a LSPR of 783 nm was estimated to be 2.41 × 10⁴ using 2,3,5,6-tetrafluoro-4-mercaptobenzoic acid (TFMBA) as a model Raman molecule. The strong SERS enhancement is due to the considerably enhanced electric field (∼40-fold at 785 nm incident light) around the AuNSs as the result of the formation of electric dipoles supported by finite element method simulation, which makes them more attractive as SERS nanotags for multiplex detection. We thus prepared seven types of SERS nanotags for spectral barcoding and 127 barcodes were generated. Such a spectral barcoding approach would open a new avenue for future multiplex applications.