Sensitive and reproducible on-chip SERS detection by side-polished fiber probes integrated with microfluidic chips

The combination of surface-enhanced Raman scattering (SERS) and microfluidic technology offers a promising solution to improve the reproducibility and reliability of SERS detection. Optical fiber SERS probes, as an important class of SERS substrates, provide a large SERS interaction area and flexible integration with microfluidic chips. In this article, a side-polished multimode fiber (SPMF) SERS probe is prepared by depositing Au nanorods on a planar polished fiber surface and integrating it into a microfluidic channel to form a glass-based microfluidic-SERS chip. The impact of SPMF residual thickness on SERS performance is thoroughly investigated, and the optimized residual thickness of 62 & mu;m is determined by considering the evanescent wave intensity, transmission loss, and experimental feasibility. The optimized microfluidic-SERS chip shows low detection limits (as low as 10-8 M for MG) and good spectral reproducibility (RSD less than 10%) due to the large SERS interaction area provided by the SPMF SERS probe and the stable liquid flow in the microfluidic channel. The chip is furtherly used to detect pesticide and antibiotic residues in tap water, with the detection limits of 10-9 M for thiram and 10-6 M for levofloxacin. This work provides an effective way to realize highly sensitive and reproducible SERS detection, and may find important applications in environmental science, food safety, and biomedicine.