The comparative strengths and limitations of Nile Red and 9-(dicyanovinyl)-julolidine (DCVJ) fluorescent dyes for detecting microplastics and nanoplastics

The study systematically compared Nile Red and 9-(dicyanovinyl)-julolidine (DCVJ) as staining agents for microplastic and nanoplastic detection. Nile Red's fluorescence is polarity-sensitive, making it useful for distinguishing hydrophobic plastics from hydrophilic materials, whereas DCVJ is more viscosity-sensitive. Using standard samples from the Hawaii Pacific University Polymer Kit 1.0, the authors confirmed that Nile Red was generally superior for detection and identification, with fluorescence emission assessed by photography and spectroscopy. However, additives in environmental microplastics could alter the color and peak emission wavelength, requiring Raman spectroscopy to confirm chemical identity.

DCVJ showed green fluorescence when binding to some microplastics, and produced a characteristic 620 nm emission with polystyrene nanobeads, attributed to dimer/excimer formation. This allowed direct observation of diffraction-limited spots by fluorescence microscopy, corresponding to single or few nanobeads. Nile Red also stained polystyrene nanobeads and gave stronger signals than DCVJ, but was prone to false positives caused by dye aggregation in aqueous solutions. These findings highlight trade-offs in sensitivity and specificity for fluorescent staining approaches in micro/nanoplastic analysis.