Nanozyme-Raman enhancement active α-MoO_3-x-CuCl₂ composite for SERS detection of phosphate species

A noble-metal-free, aggregation-independent surface-enhanced Raman scattering (SERS) platform is reported based on a bifunctional α-MoO_3-x-CuCl₂ nanocomposite for the sensitive and selective detection of phosphate species. The defect-rich α-MoO_3-x provides strong SERS enhancement, and the introduction of CuCl₂ not only enhances its peroxidase like activity, but also endows it selective response to phosphate species. The composite α-MoO_3-x-CuCl₂ can efficient catalytic oxidation of colorless tetramethylbenzidine (TMB) to blue oxidized TMB (ox-TMB), which yields a strong SERS signal. At the assay pH of 4.0, the protonated phosphate species (mainly H₂PO₄⁻) selectively coordinate with Cu²⁺, suppressing the nanozyme activity and causing a dose-dependent decrease in both colorimetric and SERS responses. Under optimized conditions, the method exhibits a linear detection range from 8.0 × 10^- 9 M to 8.0 × 10^- 5 M and a limit of detection as low as 2.0 × 10^- 9 M. The platform also demonstrates good anti-interference capability against common coexisting ions and satisfactory recoveries (103.75%-107.5%) in spiked lake water and tap water samples. This work provides a low-cost, reliable, and reproducible strategy for indirect SERS detection of phosphate species without reliance on noble metals or nanoparticle aggregation.