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The comparative strengths and limitations of Nile Red and 9-(dicyanovinyl)-julolidine (DCVJ) fluorescent dyes for detecting microplastics and nanoplastics
Summary
Scientists tested two glowing dyes used to spot microplastics and nanoplastics (tiny plastic bits small enough to potentially enter our bodies and cells) in water and environmental samples. They found that Nile Red, the more commonly used dye, generally works better for detecting and identifying microplastics, though it can sometimes give false alarms, while the less common dye DCVJ shows promise specifically for spotting the smallest nanoplastic particles under a microscope. This matters because having reliable ways to detect these tiny plastic particles is a crucial first step toward understanding how much plastic we're actually exposed to and what
Nile Red is widely used for the detection of microplastics because its fluorescence emission is sensitive to local polarity and can distinguish hydrophobic plastics from hydrophilic ones. The fluorescence of the molecular rotor, 9-(dicyanovinyl)-julolidine (DCVJ) is less sensitive to polarity but more to viscosity. DCVJ is less widely used for microplastic analysis, although it has been used to detect polystyrene nanobeads. Here, we compared these dyes with standard samples from the Hawaii Pacific University Polymer Kit 1.0 and confirmed that Nile Red, in general, was better for the detection and identification of microplastics. Fluorescence emission was analyzed using photography, as well as spectroscopy. The color and peak emission wavelength of some stained environmental microplastics were affected by additives. Raman spectroscopy was used to confirm the chemical identity of such samples. Although DCVJ emits green fluorescence on binding to some microplastics, a peak at 620 nm has been reported with polystyrene nanobeads, attributed to dimer/excimer formation. We confirmed this property and directly observed diffraction-limited spots using fluorescence microscopy, attributed to single or just a few nanobeads. Nile Red also stains polystyrene nanobeads and gave stronger signals than with DCVJ, but Nile Red was prone to false positives due to dye aggregation in aqueous solutions.