Fig. 4. SERS spectra of (A) TiO₂–Ag composite prepared at hydrothermal time (2–6 h) for TiO₂ nanorod arrays; (B) TiO₂–Ag composite in which TiO₂ nanorod calcinated before and after in air; (C) TiO₂–Ag composite, AgNPs and TiO₂ nanorod; (D) TiO₂–Ag composite for different silver-plating cycles.