Free-Standing Membrane Liquid-State Platform for SERS-Based Determination of Norfloxacin in Environmental Samples

Surface-enhanced Raman scattering (SERS) has been widely used in various fields due to high sensitivity, but it is hindered by its low repeatability. Here, we explored a highly reproducible free-standing liquid-state platform (FSM) for monitoring norfloxacin (NOR) in the environmental field. After optimizing the types of nanoparticles (NPs) and pH value in NOR solution, the relative standard deviation (RSD) of FSM SERS analysis can be stabilized below 10% (n ≥ 8), and the R2 of the calibration curve in the range of 20 µg/L–100 µg/L was 0.995. In addition, the results showed that the limit of detection (LOD) (3σ/k) of NOR was 1.3 µg/L. Moreover, the NOR in the spiked samples was successfully quantified by FSM, and the recovery rate exceeded 95%. The proposed method has the potential for rapid analysis of drug residues in environmental samples.