Junfang Li,Qinhui Xie,Junbo Li,Lei Sun,Yunfei Xie,Yukihiro Ozaki,Wei Ji
Semiconductor materials represent an ideal choice for designing surface-enhanced Raman scattering (SERS)-based sensors due to their superior thermal and chemical stability compared to conventional metal materials. However, current SERS-active semiconductor substrates have limitations such as low detection sensitivity and often complicated preparation steps, which restrict their real-life applications. In this work, for the first time the feasibility of large-area fabricating SERS-active semiconductor substrates based on screen-printing of micron-sized TiO 2 ink synthesized through a simple flame thermal-assisted method is demonstrated. The resultant TiO 2 microspherical arrays (MSAs) exhibit extraordinary SERS sensitivity with an enhancement factor of 3.28 × 10 7 , which represents one of the highest sensitivity and are the easiest strategy among the reported SERS-active semiconductor substrates. Both experiments and simulations rationalize the observed enhancement factor and propose that multiple synergistic resonances, including Mie resonance, charge-transfer resonance, and molecular resonance significantly boost the performance of semiconductor substrates. Dye-modified TiO 2 MSAs are further exploited as the sensing platform for the development of a ratiometric SERS sensor, enabling the highly sensitive, selective, low cost, and stable detection of Hg 2+ ions. This study opens up new possibilities for preparing a large-scale SERS-active semiconductor array, ultimately advancing the fields of semiconductor-based SERS sensing technology.
The main contribution of semiconductor nanomaterials to surface-enhanced Raman scattering (SERS) comes from charge transfer (CT) between the absorbing molecules and the semiconductor. However, it is still challenging to realize the combined effects of the electromagnetic mechanism (EM) and the chemical mechanism (CM) for semiconductor-based SERS substrates. Herein, we demonstrate and design double-shelled ZnO (ZnO-DS) hollow microspheres by a modified hydrothermal/solvothermal process. SERS experiments and theoretical simulations proved that the excellent SERS activity is mainly attributed to the combined effect of Mie resonances generated by the nanocavities in the unique hollow double-shell nanoparticles and the CT effect excited by special structure ZnO. Particularly, the produced ZnO-DS SERS substrates exhibited a low limit of detection (LOD, 1 × 10–7 M for 4-MPY), outstanding sensitivity (EF = 1.2 × 104), and high stability (RSD = 10.4%, over 30 days of storage at room temperature). Furthermore, benefiting from the matching of energy levels of the ZnO-DS substrate and probe molecules, the sulfhydryl molecules with similar structures could be selectively distinguished in complex environments. We visualize that this work will resolve the current dilemma between sensitivity and selective detection of SERS substrates and expect to enable the monitoring of target molecules in the environment containing complex mixtures such as food safety and environmental protection.
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