An optical sensor for discriminating the chemical compositions and sizes of plastic particles in water based on water-soluble networks consisting of polyhedral oligomeric silsesquioxane presenting dual-color luminescence†
Luminescent water-soluble networks containing the coumarin luminophore were prepared by using polyhedral oligomeric silsesquioxane (POSS) as a cross-linking point, and the optical properties of these networks in the presence and absence of various particles in water were monitored. From the emission measurements, we found that water dispersions of the POSS networks showed bimodal light-emission bands, namely in the blue and yellow regions. In particular, enhancement of the emission band in the blue region was observed upon the introduction of polystyrene particles (PSPs), poly(lactic acid) particles (PLAPs) and poly(methyl methacrylate) particles (PMMAPs), followed by changes in the color of the luminescence of the samples. In contrast, hardly any significant changes were observed when silica particles (SPs) were added. Moreover, plastic particles with diameters of less than 1 μm drastically affected the optical properties of the networks. Thus according to these results, the presence of plastic particles with sub-micron dimensions in water could be detected by changes in the color of light emitted from the POSS network from yellow to blue. Note that silica species, such as sand or rock particles, can be ignored in this system. From mechanistic studies, it was revealed that the blue-light-emission band was enhanced when the networks were adsorbed onto the surfaces of the particles. These characteristics are applicable for constructing a facile fluorescence sensor for detecting water pollution, especially nanosized plastics, denoted here as nanoplastics.