Statistical quantification of SERS signals in microfluidic flow using AuNP-bound polystyrene microparticles

Surface-enhanced Raman scattering (SERS) is a powerful analytical technique; however, its quantitative application has been limited by the instability of substrates and significant signal fluctuations. In this study, we demonstrated that 4-aminobenzenethiol (4-ATP) can be quantitatively detected through statistical analysis of SERS signal intensity distributions obtained using citrate-stabilized AuNPs, biotin-functionalized AuNPs, and gold nanoparticle (AuNP)-bound polystyrene (PS) microparticles. Raman spectra obtained in bulk aqueous solution under static conditions showed that the detection sensitivity of 4-ATP using AuNP-bound PS microparticles was approximately twice that achieved with citrate-stabilized AuNPs or biotin-modified AuNPs. Furthermore, the detection sensitivity of 4-ATP was enhanced by introducing AuNP-bound PS microparticles into a microfluidic chip and delivering an aqueous 4-ATP solution under controlled flow conditions. Analysis of the flow rate dependence of SERS signal intensity revealed that the optimal detection sensitivity for 4-ATP was achieved at a flow rate of 0.66 μL·min⁻¹, with a corresponding detection limit of 1.9 μM under these conditions. These results demonstrate that AuNP-bound PS microparticles introduced into the microfluidic chip serve as efficient SERS substrates, enabling highly sensitive and quantitative detection under flow conditions.