Biopolymer‐Templated Deposition of Ordered and Polymorph Titanium Dioxide Thin Films for Improved Surface‐Enhanced Raman Scattering Sensitivity

Abstract Titanium dioxide (TiO 2 ) is an excellent candidate material for semiconductor metal oxide‐based substrates for surface‐enhanced Raman scattering (SERS). Biotemplated fabrication of TiO 2 thin films with a 3D network is a promising route for effectively transferring the morphology and ordering of the template into the TiO 2 layer. The control over the crystallinity of TiO 2 remains a challenge due to the low thermal stability of biopolymers. Here is reported a novel strategy of the cellulose nanofibril (CNF)‐directed assembly of TiO 2 /CNF thin films with tailored morphology and crystallinity as SERS substrates. Polymorphous TiO 2 /CNF thin films with well‐defined morphology are obtained by combining atomic layer deposition and thermal annealing. A high enhancement factor of 1.79 × 10 6 in terms of semiconductor metal oxide nanomaterial (SMON)‐based SERS substrates is obtained from the annealed TiO 2 /CNF thin films with a TiO 2 layer thickness of 10 nm fabricated on indium tin oxide (ITO), when probed by 4‐mercaptobenzoic acid molecules. Common SERS probes down to 10 n m can be detected on these TiO 2 /CNF substrates, indicating superior sensitivity of TiO 2 /CNF thin films among SMON SERS substrates. This improvement in SERS sensitivity is realized through a cooperative modulation of the template morphology of the CNF network and the crystalline state of TiO 2 .