Laser speckle imaging in discrimination of zooplanktons from supermicroplastics

The presence of supermicroplastic (SMP) of less than 350 µm is on the rise in oceans, and it is often difficult to discriminate the SMPs from zooplanktons in real-time. In this study, we propose a laser speckle method in differentiating SMPs from brine shrimps, a generally used model zooplankton, and at the same time in distinguishing varied sized SMPs too. The pilot system consisting of a laser diode source of wavelength 635 nm mounted in a submersible glass sphere that has the potential of surveying in deep-sea environments illuminated a cuvette containing either polystyrene microspheres alone or mixed with brine shrimp to produce laser speckles. Such speckles recorded by a CMOS camera at 15 frames/sec for 20sec were analyzed to calculate a parameter of maximum difference between recorded frames. The results clearly differentiated the microplastics and the microplastics from the brine shrimps, thus demonstrating the possible use of the laser speckle method as a potential tool in discriminating planktons from SMPs and has implications for reaching deep-sea environments.