Detection of polystyrene nanoplastics in biological samples based on the solvatochromic properties of Nile red: application in Hydra attenuata exposed to nanoplastics

The release of nanoplastics (NP) from the weathering of microplastics is a major concern for the environment. Methods for the detection of NP in biological tissues are urgently needed because of their ability to penetrate not only in tissues but also in cells. A simple fluorescence-based methodology for the detection of polystyrene NP in biological tissues is proposed using the solvatochromic properties of Nile red. Although NPs alone increased somewhat Nile red fluorescence, a characteristic hypsochromic shift in the emission spectra was found when the dye and NP were incubated with subcellular tissue fraction. To explain this, the probe and NPs (50 and 100 nm) were prepared in the presence of increasing concentrations of two detergents (Tween-20, Triton X-100) as a proxy to phospholipids. The data revealed that both detergents readily increased fluorescence values when added to the NP and Nile red. The addition of NPs in tissue extracts blue-shifted further the emission spectra to 623 nm from the normal Nile red-lipid peak at 660 nm. The fluorescence intensity was proportional to the NP concentration. A methodology is thus proposed for the detection of NPs in laboratory-exposed organisms based on the solvatochromic properties of Nile red. The methodology was used to detect the presence of NP and changes in polar lipid contents in Hydra attenuata exposed to polystyrene NP.