Mesoporous Ag–TiO2 based nanocage like structure as sensitive and recyclable low-cost SERS substrate for biosensing applications

Abstract

We fabricated a porous Ag–TiO2 film with a nanocage (NC) like structure as a sensitive, recyclable, and low-cost SERS substrate using facile methods. The developed nanocage structure of TiO2 film was first coated on a glass plate by doctor-blade method, and then thin film of silver with an optimum thickness of 10 nm was deposited onto it using thermal evaporation method. The unique mesoporous cage-like structure of TiO2 film leads to the exceptional and non-uniform growth of Ag film. The developed Ag nanostructure is also porous, caps spherical in shape, and the average separation between two consecutive nanostructures is 10 nm. These closely decorated nanostructures of Ag produce hotspots by localising the incident electric field within the minimal volume. The unique nanocage structure of TiO2 film provides a larger effective surface area of adsorption to the analytes. Thus, the synergistic effects of Ag–TiO2 NC structure exhibit significant enhancement of 108 considering rhodamine-6g (R6G) molecule as a probe using a portable handheld Raman spectrometer. The amount of electromagnetic enhancement was further investigated by 3D FDTD simulation that matches well with the experiments. The recyclability of the developed SERS substrate was explored by placing the SERS substrate under UV illumination for 130 min. The enhanced photocatalytic activity of Ag–TiO2 NC SERS film degrades the dye molecules under UV radiation multiple times successively. Further, the Ag–TiO2 SERS substrate is highly sensitive to detect various concentrations of urea up to 1 mM covering the vital range of blood urea level. Thus, the optimised, low-cost, reusable SERS substrate can be used as level free biosensors for routine analysis of biomolecules in clinical applications.