Fabrication of an AAO-based surface-enhanced Raman scattering substrate for the identification of levofloxacin in milk

Abstract

In the process of preparing a solid surface-enhanced Raman scattering (SERS) substrate, there is a need to devise a simple and efficient method that will ensure an even distribution of nanoparticles (NPs) on the surface of the solid substrate. In this study, silver NP (Ag NP) colloids, with different particle sizes, were prepared by adjusting the pH value, and anodized aluminium oxide (AAO) was used as a template to assemble Ag NPs into AAO holes using interface self-assembly technology. Due to the limiting effect of the AAO template, the distribution of Ag NPs on the substrate was uniform. With 4-mercaptobenzoic acid (4-MBA) as a probe, the sensitivity of this SERS substrate was evaluated, with an analysis enhancement factor (AEF) of up to 1.17 × 10⁶. In addition, the signal repeatability of this SERS substrate was excellent, with a relative standard deviation (RSD) of 6.45%, and the SERS signal was basically consistent within a period of 30 days. Furthermore, the SERS identification of levofloxacin in milk was demonstrated, with a minimum detection limit of 1.88 × 10⁻⁶ M. Additionally, within the concentration range of 1 × 10⁻⁶ to 2 × 10⁻⁵ M, the levofloxacin concentration had a linear relationship with its SERS intensity, with a linear correlation coefficient as high as 0.986. The recovery rate was estimated to be between 97.61% and 107.58%, indicating the reliability of this SERS method. This simple and rapid approach is expected to be applied for the on-site measurement of antibiotics in food.