Micro-plastic detection, identification and visualisation

Recently, microplastics (MP) have emerged as global contaminants of serious concern to human and ecological health. However, identification and visualisation of MP are still a challenge, whether from wastewater, oceans, sediment or soil. Particularly when MP are mapped to visualise their distribution, the background signal from sediment and soil might be high and shield the MP signal from the analysis. Raman has recently received increasing attention, as the complementary spectrum of infrared (IR), because it can overcome the drawbacks of IR analysis including water interference, low lateral resolution and a complex spectrum. Here we show that Raman can identify and visualise MP from a soil / sand background, with almost no sample preparation, no dye, no destruction of the sample and no interference from water / organic matter / fluorescence background signals as well. By mapping image via their characteristic and fingerprint peaks, MP including polystyrene (PS), polyethylene terephthalate (PET), polyethylene (PE), polyvinyl chloride (PVC) and polypropylene (PP) can be individually identified and visualised. The lateral resolution along the focal plane is 1 μm / pixel to catch small MP down to 1 μm. In general, we successfully employed Raman mapping to identify and visualise MP as small as 1 μm from sand backgrounds. So far, the smallest particle that has been detected by Raman is a 1 µm polyamide (PA) in bottled mineral water, which was reported by Oßmann et al. Oßmann, Sarau, Holtmannspötter, Pischetsrieder, Christiansen and Dicke. However, in the current study, we can visualise and identify 5 different MP, simultaneously rather than individually. (author)