Double Metal Co-Doping of TiO2 Nanoparticles for Improvement of their SERS Activity and Ultrasensitive Detection of Enrofloxacin: Regulation Strategy of Energy Levels

In this paper, the strategy of double metals (Ni and Zn) codoping was carried out for improving SERS activity of TiO2 nanoparticles (NPs). Accordingly, pure TiO2 and different metals doped TiO2 (Zn-TiO2, Ni-TiO2 and Ni-Zn-TiO2) NPs substrates were synthesized by a sol-hydrothermal method. The results show that, compared to the other substrates, 4-mercaptobenzoic acid (4-MBA) probe molecules on the Ni-Zn-TiO2 exhibit the largest SERS enhancement, which is attributed to the contributions of double metals codoping. Ni and Zn codoping can simultaneously result in the abundant surface state levels and metal doping levels in the TiO2 band gap; both of them together promote the charge transfer from TiO2 to molecule and consequent SERS enhancement of probe molecule. And importantly, Ni-Zn-TiO2 NPs can be served as the efficient SERS-active substrate for the detection of enrofloxacin (ENR) drug. Under the optimal test conditions, the limit of detection of ENR on the 1 % Ni-1% Zn-TiO2 substrate can be reduced to 3 x 10(-10) M, which is far lower than the standard of European Union, and there is a good linear relationship in the wide low concentration range of 1 x 10(-4) similar to 1 x 10(-9) M.