SERS calibration substrate with a silent region internal standard for reliable simultaneous detection of multiple...

As the extensive use of antibiotics has led to the rapid spread of antibiotic resistance, there is an urgent need for quantitative assessment of antibiotic residues in the environment. Surface-enhanced Raman spectroscopy (SERS) has emerged as a rapid and cost-effective detection method, but it suffers from the high variability in signal intensities, its quantitative detection remains challenging. Herein, we have developed a SERS calibration substrate with a silent region internal standard, enabling simultaneous and reliable quantitative detection of three commonly antibiotics of penicillin potassium (PP), tetracycline hydrochloride (TCH) and levofloxacin (LEV). The calibration substrate is made by assembling Au @ 4-mercaptobenzonitrile (4-MBN) @ SiO₂ on silicon wafer. The chemically-inert silica shell allows the substrate to remain SERS active for more than 24 weeks in the air. The v_C ≡ N of 4-MBN in the silent region of 1800-2800 cm^-1 provides an effective reference for correcting Raman signal fluctuations. The relative SERS intensity by normalizing to the internal standard (IS) of v_C ≡ N shows a linear response against to the logarithmic concentration with a correlation coefficient of 0.997, 0.976, 0.998 and a limit of detection (LOD) of 26.9, 28.2, 2.4 nM for PP, TCH and LEV, respectively. Furthermore, simultaneous detection and principal component analysis (PCA) of these antibiotics in lake water with a concentration range of 1-100 mg/L can achieve a sensitivity and specificity of 100 %. This novel quantitative technique of using this SERS calibration substrate shows promises as a high-throughput platform for multiple trace antibiotics analysis.