Lithium-doped ZrO₂ nanoparticles for SERS-based norfloxacin drug detection

Surface-enhanced Raman scattering (SERS) spectroscopy is a highly specific and ultrasensitive analytical technique; thus, it is an ideal candidate for therapeutic drug monitoring. However, SERS measurements of drugs in a sample are inevitably affected by the environment. In this study, we synthesized ZrO₂ nanoparticles (NPs) doped with the first group of elements (Li, Na, and K) in the main block and evaluated their SERS performance. The results showed that Li-ion doping could significantly enhance the SERS effect, and the degree of enhancement depended on the type and concentration of the doped ions. Compared with the highly stable ZrO₂, Li ion-doped ZrO₂ (Li-ZrO₂) exhibited a significant increase in SERS activity. In particular, 1 % Li-ZrO₂ NPs exhibited excellent SERS enhancement with an enhancement factor (EF) of 2.60 × 10⁴, which was attributed to the decreased band gap and improved the charge transfer (CT) process after Li ion doping. The adsorption capacity of the Li-ZrO₂ NPs for norfloxacin (NOR) molecules was gradually saturated with time. In addition, both acidic and alkaline conditions were unfavorable for NOR detection by the substrate. The SERS intensity exhibited a linear relationship within the NOR concentration range of 10^-3-10^-6 mol/L, and approximately 97.51 % of the active ingredients were detected, with a competitive detection limit of 10^-6 mol/L. Furthermore, NOR detection is cost-effective and time-efficient, and the results of our study can aid in the research process and support practical applications. The proposed study provides a guidance for improving the SERS activity of semiconductors for sensing.