Three-dimensional urchin-like K₂Ti₈O₁₇ / Ag NPs composite as a SERS substrate for detecting folic acid and thiram

The three-dimensional (3D) semiconductor/noble metal composite substrates for surface-enhanced Raman scattering (SERS) have garnered increasing interest due to their excellent optical and chemical properties, as well as the capacity to trigger both electromagnetic mechanism (EM) and chemical mechanism (CM) simultaneously. In this work, a facile 3D urchin-like K₂Ti₈O₁₇/Ag nanoparticles (Ag NPs) composite substrate is designed for multi-purpose SERS sensing. K₂Ti₈O₁₇, as a dielectric medium, improves the electric field environment around Ag NPs, which is consistent with finite-different time domain (FDTD) results, and enhances the SERS performance of the K₂Ti₈O₁₇/Ag composite substrate. Besides, the efficient "donor-bridge-acceptor" charge transfer mode, explored through energy level calculations and enhanced utilization of incident light, further strengthens the SERS performance. Results show that the prepared K₂Ti₈O₁₇/Ag NPs substrate exhibits high detection sensitivity, with 10^-11 and 10^-12 M limits in detecting Methylene Blue (MB) and Crystal Violet (CV), and the enhancement factors (EFs) of 2.66 × 10⁹ and 6.07 × 10⁹, respectively. At the same time, the composite substrate also possesses good signal uniformity (RSD = 10.5 %) and promising photocatalytic ability. For practical applications, the prepared K₂Ti₈O₁₇/Ag NPs substrate can detect folic acid of 10^-7 M in the diluted serum environment and thiram of 10^-8 M in lake water, respectively. The urchin-like K₂Ti₈O₁₇/Ag NPs substrate expands the range of 3D semiconductor composite SERS substrates, which is expected to be used for biosensing and trace analysis of harmful substances.