A fiber-optic SERS probe based on femtosecond laser-processed square microcavity with high-sensitivity detection of antiepileptic drugs

A high-sensitivity and high-stability fiber-optic surface-enhanced Raman scattering (SERS) probe based on a square microcavity structure is proposed. The probe is fabricated by femtosecond laser processing technology to precisely prepare a square microcavity with dimensions of 13 × 13 × 60 μm on the core of a multimode optical fiber. Silver nanoparticles with an average particle size of approximately 44 nm were uniformly deposited on the inner surface of the microcavity using a sol self-assembly method to functionalize the structure. Experimental results indicate that the SERS probe exhibits optimal enhancement performance when the self-assembly time is 40 min at a the same experimental conditions. Using Methylene Blue as the probe molecule, the probe achieves a detection limit of 10 −10  M. The relative standard deviation of the characteristic peak intensity is less than 5%, demonstrating good reproducibility. The calculated analytical enhancement factor is as high as 1.19 × 10 9 . In the simulated blood test, the probe achieved a detection limit of 1 μg/mL for the antiepileptic drug 10-monohydroxy derivative (MHD), with a linear correlation coefficient R 2 of 0.9895 for gradient concentrations. Therefore, the probe exhibits excellent in-situ detection capability and operational stability, providing a new and reliable means for the application of SERS technology in trace substance detection and in-situ analysis.