Boosting SERS Performance of TiO2 Microspheres via Phytic Acid Modification: Application to Bisphenol A Detection in Consumer Products

Surface-enhanced Raman scattering (SERS) based on semiconductor substrates offers advantages of low cost and high stability over noble metals, but its practical application is hindered by intrinsically weak signal enhancement. Herein, we report a simple molecular engineering strategy to dramatically boost the SERS performance of TiO2 microspheres through phytic acid (PA) modification. The PA molecules anchor onto TiO2 surfaces via Ti–O–P bonds, forming PA/TiO2 composites in a single-step postsynthesis process. The optimized PA/TiO2 substrate achieves an enhancement factor (EF) of 1.2 × 107─comparable to typical noble metal substrates─and enables detection of the probe molecule 4-mercaptobenzoic acid at concentrations as low as 1 × 10–9 mol/L. Comprehensive mechanistic investigation reveals a synergistic effect: (i) PA-induced coffee-ring aggregation for analyte enrichment, (ii) Mie resonance from the TiO2 microspheres (∼253 nm) for electromagnetic field enhancement, and (iii) charge transfer (CT) resonance at the PA/TiO2 interface for additional chemical contribution, supported by density functional theory calculations and finite-difference time-domain simulations. Leveraging this high-performance platform, we construct an SERS sensor for the endocrine disruptor bisphenol A (BPA), a common contaminant in thermal paper products. The sensor exhibits excellent analytical performance: a limit of detection (LOD) of 4.7 × 10–7 mol/L, a wide linear range from 5.0 × 10–6 to 1.0 × 10–3 mol/L (R2 = 0.9971), and satisfactory spike-recovery results (97.8–103.0%) in real thermal paper samples. This work demonstrates that molecular-level surface engineering offers a scalable and cost-effective route to high-performance semiconductor SERS substrates for environmental monitoring applications.