Three-dimensional hierarchical anatase@rutile TiO2 nanotree array films decorated by silver nanoparticles as ultrasensitive recyclable surface-enhanced Raman scattering substrates

In this paper, we report a three-dimensional (3D) hierarchical nanostructure as a surface-enhanced Raman scattering (SERS) sensor by decorating Ag nanoparticles on a TiO2 nanotree (TNT) array film via a simple two-step hydrothermal treatment and a magnetron sputtering technique for the first time. The sensitivity, recyclability, and uniformity of the SERS-active substrates were investigated using Rhodamine 6G (R6G) as the probe molecule. A detection limit of 1.0 x 10(-12) M R6G molecules and an enhancement factor of 5.29 x 10(5) were achieved on the 3D hierarchical TNT array film with 60 s Ag-sputtering. More importantly, the optimized TNT/Ag also exhibits excellent recyclability and uniformity. The relative standard deviation in the intensity of Raman vibration mode (1506 cm(-1)) was about 1.2%. Furthermore, the 3D hierarchical nanostructure was more efficient than the 1D nanostructure for SERS measurements. The excellent SERS performance is attributed to the formation of high-density hot spots for 3D nanostructure as well as the synergistic effects of electromagnetic and charge transfer. Moreover, the anatase@rutile mixed phase provides an additional charge transfer effect, which can lead to further enhancement of the Raman signal. The results show that the TNT/Ag nanostructure can be a promising candidate for SERS sensors. (C) 2017 Published by Elsevier B.V.