TiO2 compact layer induced charge transfer enhancement in a three-dimensional TiO2–Ag array SERS substrate for quantitative and multiplex analysis

Abstract

A highly sensitive and uniform surface-enhanced Raman scattering (SERS) substrate is the guarantee for reliable quantitative analysis. Herein, a three-dimensional TiO₂–Ag SERS substrate was prepared by growing a TiO₂ nanorods (NRs) array on a TiO₂ compact layer (c-TiO₂), followed by modification with Ag nanoparticles (AgNPs). The synergy between the c-TiO₂, semiconductor TiO₂ NRs and the plasmonic AgNPs collaboratively endowed it with high sensitivity, in which c-TiO₂ effectively blocked the recombination of electrons and holes, and the charge transfer enhancement contributed 10-fold improvement over that without the c-TiO₂ substrate. Besides the high sensitivity, the TiO₂–Ag hybrid array SERS substrate also showed quantitative and multi-component detecting capability. The limit of detection (LOD) for crystal violet (CV) was determined to be 10⁻⁹ M even with a portable Raman instrument. The TiO₂–Ag composite structure was extended to detect organic pesticides (thiram, triazophos and fonofos), and the LODs for thiram, triazophos and fonofos were measured to be 10⁻⁷ M, 10⁻⁷ M and 10⁻⁶ M, respectively. In addition, the realistic simulation detecting pesticide residues for a real sample of dendrobium was demonstrated. The sensitive, quantitative and multiplex analysis of the TiO₂–Ag hybrid array substrate indicated its great potential in the rapid detection of pesticide residues in real samples.