Double-sided plasmonic metasurface for simultaneous biomolecular separation and SERS detection

•We realize high-selectivity bimolecular separation and simultaneous ultrasensitive SERS detection by double-sided hierarchical porous membrane-like plasmonic metasurface.•Our hierarchical groove-pore structure supports a peculiar cascaded electromagnetic near-field enhancement mechanism.•As a SERS substrate, our plasmonic metasurface meet the requirement of ultrahigh sensitivity, uniformity, repeatability, and polarization independence.•Our SERS substrate has double-side SERS responsivity and ultrahigh mechanical flexibility.