A SERS stamp: Multiscale coupling effect of silver nanoparticles and highly ordered nano-micro hierarchical substrates for ultrasensitive explosive detection

In this study, we reported a novel highly ordered nano-micro hierarchical structure on flexible polydimethylsiloxane (PDMS) layer as a SERS stamp for ultrasensitive detection, which can generate huge SERS signals with silver nanoparticles (AgNPs) owing to a multiscale coupling electromagnetic enhancement mechanism. Highly ordered nanowrinkles were prepared by oxygen plasma and stretching treatment of PDMS. Indeed, a tactfully designed zigzag micropattern can efficiently reduce the fracture defects of nanowrinkles because the contraction force can be lessened at releasing step. This proposed substrate has high reproducibility and uniformity that the relative standard deviation (RSD) was below 7 %. With uniform hot spots on this novel flexible SERS substrate, 2, 4, 6-trinitrotoluene (TNT) residues can be detected on coarse surfaces of target item. A molecule interaction mechanism of Meisenheimer complex was applied to combine AgNPs and nanowrinkles for highly sensitive detecting TNT. The detection sensitivity of TNT molecules can achieve a limit of 10−13 mol L−1. Additionally, a practical application was proceeded by wiping the cloth bag to detect the TNT residues with a limit of 10−9 mol L−1. This demonstrated stamp-like flexible substrate showed unique SERS activity and non-invasive sampling, it is expected to be a promising tool for the explosive, drug and environmental pollutant in field-detection.