Ultrasensitive SERS detection using UV-ozone treated Nb2O5−x nanosheets coupled with plasmonic nanoparticles: an integrated experimental and theoretical study

Abstract

Defect engineering in semiconductors is one of the most effective techniques to enhance the sensitivity of the surface-enhanced Raman scattering (SERS) effect in semiconductor substrates. By carefully tailoring the oxygen vacancies in a wide bandgap semiconductor, such as Nb₂O₅, the charge transfer processes can be optimized to strengthen the chemical enhancement mechanism (CM). In the present study, oxygen vacancies were incorporated into 2D Nb₂O₅ nanosheets via a cost-effective UV-ozone treatment and were further integrated with plasmonic Ag, Au nanoparticles (NPs) to harness the synergistic effect of electromagnetic (EM) and CM enhancement mechanisms to contribute towards a superior SERS performance. An extraordinary enhancement factor of 6.75 × 10⁸ with a detection limit of 10⁻¹⁰ M was achieved with Ag nanoparticle decorated Nb₂O₅ nanosheets after UV-ozone treatment, for the detection of malachite green (MG) molecules. Remarkably, the same substrates were also effective for the sensitive detection of the antibiotic ciprofloxacin (CIP). The excitation wavelength has a major impact, which has been chosen in a way to maximize the contributions of both mechanisms. Furthermore, density functional theory (DFT) calculations and finite element method (FEM)-based simulations were employed to unravel the underlying mechanisms and to delineate their individual contributions to the overall SERS enhancement. This work paves a practical and scalable pathway to engineer highly sensitive and stable SERS substrates, underscoring the potential of defect-tailored metal–semiconductor hybrids for applications in environmental monitoring, food safety, and analytical sensing.