Fluorescent nanoplastics: What steps are needed towards a representative toolkit?

Degradation of plastic waste in the environment induces the formation of plastic particles, that can be either microplastics (MPs, < 5 mm) or nanoplastics (NPs, < 1000 nm). Their presence poses an emerging concern for environmental and human health, but the scale of the risk remains unknown due to the various challenges in their proper detection and identification. Fluorescence-based analytical methods are commonly employed for toxicological and/or exposure model studies, as well as environmental studies. Aiming at researchers assessing the effect and behaviour of NPs within exposure and imaging studies, this review critically explores different strategies for using or synthesizing fluorescent NPs, starting with highlighting relevant overlap from fluorescent MP work, to identifying current knowledge and methodological gaps. Unfortunately, the prevailing strategies for obtaining fluorescent NPs, especially using commercially available polystyrene (PS) beads and dye loading synthesis routes, are inadequate and not representative of environmental NPs, although in recent years promising alternatives have been provided. For that reason, we recommend various approaches for making fluorescent model NP particles. The article ends with concluding remarks and an outlook on the challenges in NP detection, with a suggested "roadmap" to aid the reader in determining the ideal approach of making or using fluorescent NPs in their own field of application.