Here we propose a simple, fast on-site MuScan® method that automatically analyses the number of micro-plastic particles in a sample. The Muscan® method reliably detects and quantifies micro-plastics, even down to 1 µm in size. Current simple methods often rely on manually viewing and counting micro-plastics in a sample under a microscope. More advanced techniques use Fourier-transform infrared spectroscopy (FT-IR), Raman spectrometry, and chromatography/mass spectrometry (GC/MS, ICP-MS). However, with these methods a reliable, objective quantification and determination of the size of micro-plastics in larger sample volumes is not possible or can be very cumbersome. As these advanced methods require large financial investments, need a high degree of expertise and are not easy to perform on-site, there is an urgent need for a more rapid, simple and cost-effective method.