A simple and efficient self-approach strategy was used to apply ultrasensitivity and self-revive ZnO–Ag hybrid surface-enhanced Raman scattering (SERS) sensors for the highly sensitive and selective detection of explosive TNT in both solution and vapour conditions. The good ultrasensitive sensing performance is a result of the abundant Raman hot spots, which were spontaneously formed in a reversible way by the self-approaching of flexible ZnO–Ag hybrid nanorods driven by the capillary force of solvent evaporation. Moreover, the enhancement effect was repeatedly renewed by the reconstruction of molecular bridges, which could selectively detect TNT with a lower limit of 4 × 10⁻¹⁴ M. In addition, TNT vapor was also tested under this sensor, whereby once the ZnO–Ag NRs hybrid substrate was dipped in TNT, this substrate could detect the existence of TNT even in 5 detection cycles via a capillarity-constructed reversible hot spots approach. Compared with other pure Ag-based SERS sensors, this ZnO–Ag hybrid SERS sensor could rapidly self-revive SERS-activity by simple UV light irradiation and could retain stable SERS sensitivity for one month when used for TNT detection. This stable and ultrasensitive SERS substrate demonstrates a new route to eliminate the oxidized inactive problem of traditional Ag-based SERS substrates and suggests promising use in the applications of such hybrids as real-time online sensors for explosives detection.

We report on the large-scale synthesis of Ag-nanoparticle (Ag-NP) decorated ZnO-mesoporous-nanosheets (NSs) grafted on a flexible carbon fiber cloth (CFC), as sensitive and reproducible surface enhanced Raman scattering (SERS) substrates with excellent flexibility. The composite SERS-substrates are achieved by a combination of atomic layer deposition of ZnO-seeds on each fiber of the CFC (denoted as ZnO-seeds@CFC), chemical bath deposition and subsequent pyrolysis for the creation of ZnO-mesoporous-NSs grafted on ZnO-seeds@CFC, and ion-sputtering of Ag-NPs on the ZnO-mesoporous-NSs. As abundant SERS “hot spots” are generated from the electromagnetic coupling of the densely distributed Ag-NPs, and the semiconducting ZnO-mesoporous-NSs also have chemical supporting enhancement and distinct molecule adsorbing abilities, the composite SERS-substrates demonstrate high SERS-sensitivity with good signal reproducibility. As a trial for potential applications, the composite SERS-substrates were used to identify pesticides and highly toxic polychlorinated biphenyls (PCBs), and low concentrations down to 10⁻⁷ M for methyl parathion and 5 × 10⁻⁶ M for PCB-77 were reached, respectively, showing promising potential for the SERS-based rapid detection of toxic organic pollutants in the environment.

3D biomimetic superhydrophobic Ag micro/nano-pillar array (AMA) surfaces as SERS substrates were prepared for ultrasensitive and reproducible detection of explosives such as picric acid (PA) and 3-nitro-1,2,4-triazol-5-one (NTO) by a simple, efficient, and inexpensive hydrophobic condensation strategy. We took advantage of different kinds of Si pillar arrays (biomimetic structure based on cicada wing topography) as templates for electrochemical deposition generation of 3D AMA. We studied the effects of biomimetic superhydrophobicity and different AMA micro-morphology on SERS performance from a macro and micro perspective, respectively. For the first time, simple hydrophilic organic synthesis process was also conducted to improve poor water-solubility of toxins to aid detection. Such SERS sensors exhibited high sensitivity to rhodamine 6G (R6G) in a low concentration of 10⁻¹⁵ mol L⁻¹, PA in a low concentration of 10⁻¹² mol L⁻¹, and NTO in concentration as low as 10⁻¹³ mol L⁻¹ after hydrophilic synthesis. This method of hydrophobic condensation of substrates resolved the problems for extremely low concentration of organic solutions of toxins in difficulty to SERS detection. Furthermore, it was found to be very useful to improve practical application of portable Raman detection devices to detect low-solubility protonic toxins.

An efficient and green approach was used to fabricate novel and low-cost surface-enhanced Raman scattering (SERS) spectroscopy sensors based on 4-aminothiophenol (4-ATP) functionalized ZnO–Ag hybrid nanoflowers for the detection of explosives. Such SERS sensors exhibited high sensitivity to rhodamine 6G (R6G) at a low concentration of 10⁻¹² M and an enhancement factor of over 4.12 × 10⁶ was achieved. Moreover, the Raman-inactive trinitrotoluene (TNT) initiated the high Raman scattering of non-resonated 4-ATP through the formation of a π-donor–π-acceptor interaction between the π-acceptor, TNT, and the π-donor, the 4-ATP–Ag–ZnO complex, on the flower-like hybrids. Because this π-donor–π-acceptor interaction could effectively induce the “hot spots” for SERS, TNT concentrations as low as 5 × 10⁻⁹ M could be detected. Furthermore, other derivatives of TNT were also explored, and this sensor exhibited better selectivity for TNT than other similarly structured explosives. The low-cost hybrid SERS substrates presented good sensitivity and reproducibility for the analytes employed, demonstrating promising application in forensic science and homeland security.