A smartphone label-free and automated thermo-analytical method based on image analysis to detect microplastics

Microplastics (MPs) are in some ways the expected product of man-made plastics that are considered as a pollutant ubiquitous in the environment. This is particularly notorious in continental waters, along coastlines, and especially in the North Pacific Gyre, sometimes called the Pacific Garbage Patch. Even now, there is growing concern that MPs can harm wildlife, enter the food chain, and end up in the human body. Therefore, the development of new, simpler and easily automated analytical systems is needed to assess the extent of MPs contamination in the environment. In this work, we present a low-cost analytical method capable of identifying, counting, and sizing MPs and differentiating them from non-plastic particles in less than 5 min after performing image-based analysis during a heating ramp between 25 and 220 °C. Using a smartphone and its camera and a dedicated algorithm, semi-crystalline and amorphous MPs such as polyethylene, polypropylene and polystyrene were efficiently identified by determining whether they melt or change size. The method was tested on spiked soil and sand samples as well as on real samples with successful results. A large number of particles can be analyzed simultaneously using an algorithm that eliminates the need for manual operations. The method is presented to be used as the first necessary step to investigate the level of threat (if any) of this new ubiquitous presence.