ScroBiculate sub-10 nm nanocavity arrays as effective sers substrate for the trace determination of 3,3′,4,4′— Polychlorinated biphenyls

•Densely arranged nanocavity array have been constructed on the silver-based SERS substrate.•The SERS substrate demonstrated remarkable SERS sensitivity and high homogeneity for SERS signal distribution across the substrate surface.•High SERS sensitivity for R6G and PCB77 molecules have been achieved.•Cone-shaped nanocavity benefits the captivity of PCBs molecules.