Hierarchical Particle-In-Quasicavity Architecture for Ultratrace Raman Sensing and Its Application in Real-Time Monitoring of Toxic Pollutants.

Unstable detection environment is one of the biggest interferences for surface-enhanced Raman spectroscopy (SERS) using in real-time monitoring of toxic pollutants, leading to unreliable results. To address this problem, we have designed and prepared a cavity-based particle-in-quasicavity (PIQC) architecture composed of hierarchical ZnO/Ag nanosheets and nanoprotrusions for improving the SERS performance under a liquid environment. Benefitting from the special cascaded optical field mode, the PIQC ZnO/Ag exhibits excellent SERS detectability, with 10 M of limit of detection for rhodamine 6G and 12.8% of signal relative standard deviation value. Furthermore, by means of a microfluidic chip, this PIQC structure is proved to have the quantitative analysis feasibility and realizes real-time monitoring of the 3,3',4,4'-tetrachlorobiphenyl, a representative global environmental hazard, under the flowing environment. The strategy in this paper provides a brand new idea to promote the application of SERS in contaminant monitoring and is also instructive for light control in other optical fields.