Silver Nanoparticles Coated Zinc Oxide Nanorods Array as Superhydrophobic Substrate for the Amplified SERS Effect

A superhydrophobic substrate that combines the superhydrophobic condensation effect and high enhancement ability of silver nanoparticle coated zinc oxide nanorods array (Ag@ZnO) is explored for surface enhanced Raman scattering (SERS). The effects of water contact angle and droplet volume on the final SERS signal intensity are also investigated for the first time. Our results indicate the superhydrophobic substrate could exhibit 3-fold signal enhancement more than the ordinary hydrophilic Ag@ZnO substrate due to the superhydrophobic condensation effect. This signal amplification effect is affected by the water contact angle and water droplet volume on the substrate, i.e., (1) the higher the contact angle is, the higher the SERS signal is; (2) the SERS intensity fluctuates as the droplet volume increases, and proper volume, not the largest one, should be chosen to achieve a stronger signal. Most importantly, this superhydrophobic substrate with high signal reproducibility is successfully applied to detect small molecules such as adenine and melamine, with the detection limits of 1 order of magnitude less than those on the hydrophilic Ag@ZnO substrate. It is expected this superhydrophobic SEAS substrate can be widely used in the trace analysis in the future.