Label-free detection of polystyrene nanoparticles in <i>Daphnia magna</i> using Raman confocal mapping

Micro- and nanoplastic pollution has emerged as a global environmental problem. Moreover, plastic particles are of increasing concern for human health. However, the detection of so-called nanoplastics in relevant biological compartments remains a challenge. Here we show that Raman confocal spectroscopy-microscopy can be deployed for the non-invasive detection of amine-functionalized and carboxy-functionalized polystyrene (PS) nanoparticles (NPs) in <i>Daphnia magna</i>. The presence of PS NPs in the gastrointestinal (GI) tract of <i>D. magna</i> was confirmed by using transmission electron microscopy. Furthermore, we investigated the ability of NH₂-PS NPs and COOH-PS NPs to disrupt the epithelial barrier of the GI tract using the human colon adenocarcinoma cell line HT-29. To this end, the cells were differentiated for 21 days and then exposed to PS NPs followed by cytotoxicity assessment and transepithelial electrical resistance measurements. A minor disruption of barrier integrity was noted for COOH-PS NPs, but not for the NH₂-PS NPs, while no overt cytotoxicity was observed for both NPs. This study provides evidence of the feasibility of applying label-free approaches, <i>i.e.</i>, confocal Raman mapping, to study PS NPs in a biological system.