Determination of aqueous antibiotic solutions using SERS nanogratings

The emergence of antibiotics and their active metabolites in aquatic ecosystem has motivated the development of sensitive and reliable sensors to monitor traces of antibiotics and metabolites in drinking water sources (i.e. surface water). The surface enhanced Raman scattering (SERS) technique, which is widely recognized as a high sensitivity method for molecular vibrational detection, is potentially a powerful tool for trace environmental contamination analysis. The main goal of this work is to demonstrate pharmaceutical and metabolite multiplexing detection using the SERS approach. Periodic metallic nanostructures were fabricated using laser interference lithography (LIL) and used as SERS substrates (platform that supports the SERS effect). The LIL method allowed excellent substrate-to-substrate geometric parameters variations; for instance, the variations in periodicity were determined to be less than 1%. A common fluoroquinolone (FQ) parent-and-metabolite pair, enrofloxacin (ENRO) and ciprofloxacin (CIPRO), was targeted for multiplexing detection on the relative uniform substrates fabricated by LIL. The quantifications of the analytes mixtures were achieved by chemometric analysis (i.e. non-negative matrix factorization with alternating least square algorithm (NMF-ALS)). The limit of the quantification (LOQ) of the present method is in the ppm-level with less than 10% spatial variation in the SERS signal.