Remarkable surface-enhanced Raman scattering on self-assembled {201} anatase

Abstract

Semiconductors exhibit great potential as a surface-enhanced Raman scattering (SERS) substrate due to their low cost, stability, and biocompatibility. However, their application has been essentially restricted by their intrinsically low SERS sensitivity (10–10²). Herein, sea urchin-like TiO₂ was obtained by a self-assembled growth of crystals enclosed with the {201} facet. The high-symmetric spiny spheres exhibited appreciable Raman enhancement factors (EFs) of 1.6 × 10⁶, three orders of magnitude higher than those asymmetric TiO₂ with exposed {101}, {001}, and {100} facets. The greatest charge transfer upon dopamine adsorption occurred on {201} TiO₂ due to its high density of unoccupied t_2g orbitals, partly contributing to the excellent SERS performance. More importantly, the sea urchin-like spheres created high-density hotspots evenly distributed in the vicinity of sharp tips and at narrow gaps between the spines, enabling a strong electromagnetic field enhancement (1.4 × 10⁴). Benefiting from the specific electronic and morphologic properties, the self-assembled {201} TiO₂ exhibited superior SERS performance in terms of both intensity and reproducibility. The insights gained from this study open a new avenue to improve the SERS performance of semiconductors for applications in biomedical analysis, food detection, and toxicity tests.