Staining methodologies for microplastics screening

Whether intentionally manufactured or resulting from fragmentation of larger plastic debris, micro-sized plastic fragments (<5 mm), commonly referred to as microplastics, are ubiquitous in the environment. Therefore, correctly ascertaining their prevalence, in order to accurately estimate their environmental, ecotoxicological and health impacts, is of the utmost importance. However, simple, straightforward and efficient methods for their routine monitoring remain scarce. In this scenario, staining techniques, following adequate sample pre-processing, have been vastly used as a simple method to visually sort microplastics in diverse matrices. Nile Red, despite its widespread use, also has limitations, thereby preventing it from being applied at a large(r) scale. Herein, we overview the different types of dyes that have been used in microplastic detection studies, with the purpose of assessing the state of the art concerning new and alternative methods for visual inspection of microplastics along with each method's features that underly their potential for large-scale applicability.