Plasmonic liquid marbles: A miniature substrate-less SERS platform for quantitative and multiplex ultratrace molecular detection

Inspired by aphids, liquid marbles have been studied extensively and have found application as isolated microreactors, as micropumps, and in sensing. However, current liquid-marble-based sensing methodologies are limited to qualitative colorimetry-based detection. Herein we describe the fabrication of a plasmonic liquid marble as a substrate-less analytical platform which, when coupled with ultrasensitive SERS, enables simultaneous multiplex quantification and the identification of ultratrace analytes across separate phases. Our plasmonic liquid marble demonstrates excellent mechanical stability and is suitable for the quantitative examination of ultratrace analytes, with detection limits as low as 0.3fmol, which corresponds to an analytical enhancement factor of 5×10⁸. The results of our simultaneous detection scheme based on plasmonic liquid marbles and an aqueous-solid-organic interface quantitatively tally with those found for the individual detection of methylene blue and coumarin. Taking all the marbles: Plasmonic liquid marbles are used in conjunction with surface-enhanced Raman spectroscopy for the simultaneous multiplex quantification and identification of ultratrace analytes across separate phases (see picture) with a detection limit as low as 0.3fmol, which corresponds to an analytical enhancement factor of 5×10⁸. The results quantitatively tally with those obtained for the individual detection of the analytes.