MicroMetaSense:\nCoupling Plasmonic Metasurfaces with\nFluorescence for Enhanced Detection of Microplastics in Real Samples

Diverse analytical techniques are\nemployed to scrutinize microplastics\n(MPs)pervasive at hazardous concentrations across diverse\nsources ranging from water reservoirs to consumable substances. The\nlimitations inherent in existing methods, such as their diminished\ndetection capacities, render them inadequate for analyzing MPs of\ndiminutive dimensions (microplastics: 1–5 μm; nanoplastics:\n< 1 μm). Consequently, there is an imperative need to devise\nmethodologies that afford improved sensitivity and lower detection\nlimits for analyzing these pollutants. In this study, we introduce\na holistic strategy, i.e., MicroMetaSense, reliant on a metal-enhanced\nfluorescence (MEF) phenomenon in detecting a myriad size and types\nof MPs (i.e., poly(methyl methacrylate) (PMMA) and poly(ethylene terephthalate)\n(PET)) down to 183–205 fg, as well as validated the system\nwith real samples (tap and lake) and artificial ocean samples as a\nreal-world scenario. To obtain precise size distribution in nanometer\nscale, MPs are initially processed with an ultrafiltration on-a-chip\nmethod, and subsequently, the MPs stained with Nile Red dye are subjected\nto meticulous analysis under a fluorescence microscope, utilizing\nboth a conventional method (glass substrate) and the MicroMetaSense\nplatform. Our approach employs a metasurface to augment fluorescence\nsignals, leveraging the MEF phenomenon, and it demonstrates an enhancement\nrate of 36.56-fold in detecting MPs compared to the standardized protocols.\nThis low-cost ($2), time-saving (under 30 min), and highly sensitive\n(183–205 femtogram) strategy presents a promising method for\nprecise size distribution and notable improvements in detection efficacy\nnot only for laboratory samples but also in real environmental samples;\nhence, signifying a pivotal advancement in conventional methodologies\nin MP detection.