Controllable fabrication of Ag-NP-decorated porous ZnO nanosheet arrays with superhydrophobic properties for high performance SERS detection of explosives

An efficient hydrophobic condensation surface was developed and used as an ultrasensitive surface-enhanced Raman scattering (SERS) sensor. The sensors were based on ZnO-Ag hybrid mesoporous nanosheets (MNSs) grafted on ordered Si micropillar arrays for detection of explosives. The hybrid SERS substrates were prepared via three steps: first, the ZnO seeds were precoated onto highly ordered Si micropillar arrays through atomic layer deposition; second, porous ZnO nanosheet arrays were grown based on ZnO seeds via chemical bath deposition by a secondary solvent addition method. Finally, ion-sputtering of Ag-nanoparticles (NPs) onto the ZnO MNSs was performed. Because the ordered Si micropillar arrays with a high aspect ratio provided 3D framework structures, the 3D ZnO MNSs of the Si pillar also generated three types of SERS active "hot spots". And the excellent SERS effect induced by the three different "hot spots" from 3D structures was further theoretically confirmed by simulating the electromagnetic field distributions. What's really interesting was that the prepared substrates showed superhydrophobicity. Based on the hydrophobic condensation strategy, hazardous explosives of NTO, FOX-7 were label-free detected in real samples like tap water and river water. And these samples, which were spiked with nitrophenylamine explosive TNT, were also selectively detected by secondary solvent addition under the 4-aminothiophenol (4-ATP)-modified superhydrophobic surface. Because the electronic transfer compensation effect of the hybrids ensured the stability of substrates, ZnO-Ag MNS hybrid substrates could be used for ultrasensitive detection of explosives after being stored for 49 days. Therefore, these effective SERS substrates demonstrated a promising application in forensic science and homeland security.