Identification of microplastics using 4-dimethylamino-4'-nitrostilbene solvatochromic fluorescence.

Giuseppe Sancataldo,Vittorio Ferrara,Francesco Paolo Bonomo,Valeria Vetri,Mariano Licciardi,Bruno Giuseppe Pignataro,Delia Francesca Chillura Martino

doi:10.1002/jemt.23841

Abstract

In this work, we introduce the use of 4‐dimethylamino‐4′‐nitrostilbene (DANS) fluorescent dye for applications in the detection and analysis of microplastics, an impendent source of pollution made of synthetic organic polymers with a size varying from less than 5 mm to nanometer scale. The use of this dye revealed itself as a versatile, fast and sensitive tool for readily discriminate microplastics in water environment. The experimental evidences herein presented demonstrate that DANS efficiently absorbs into a variety of polymers constituting microplastics, and its solvatochromic properties lead to a positive shift of the fluorescence emission spectrum according to the polarity of the polymers. Therefore, under UV illumination, microplastics glow a specific emission spectrum from blue to red that allows for a straightforward polymer identification. In addition, we show that DANS staining gives access to different detection and analysis strategies based on fluorescence microscopy, from simple epifluorescence fragments visualization, to confocal microscopy and phasor approach for plastic components quantification.

Highlights

In the last century, plastics production has progressively increased, since these materials have succeeded as constituents of most of the everyday life objects
We introduce the use of 4-dimethylamino-40-nitrostilbene (DANS) fluorescent dye for applications in the detection and analysis of microplastics, an impendent source of pollution made of synthetic organic polymers with a size varying from less than 5 mm to nanometer scale
The experimental evidences presented demonstrate that DANS efficiently absorbs into a variety of polymers constituting microplastics, and its solvatochromic properties lead to a positive shift of the fluorescence emission spectrum according to the polarity of the polymers

Summary

| INTRODUCTION

Plastics production has progressively increased, since these materials have succeeded as constituents of most of the everyday life objects. FTIR and Raman spectroscopies implemented in imaging mode have revealed high potentiality allowing for noninvasive identification and characterization of MPs by mapping chemical properties of the sample with microscale spatial resolution (Harrison, Ojeda, & Romero-Gonzalez, 2012; Tagg, Sapp, Harrison, & Ojeda, 2015) These methods provide a large amount of information, including possible presence of pollutants and modifications due to environmental conditions, they may be time consuming especially for the analysis a relevant number of particles (Anger et al, 2018). In situ 4D (x,y,z,t) measurements in different matrices should be accessible of samples coming from seawater, soils, and biological tissues In this context, fluorescence microscopy has emerged as an ideal tool for these applications providing fast high-resolution analysis of MPs through the use of fluorescent dyes, small organic molecules whose spectral properties critically change depending on the interaction with the environment (Cole, 2016). We present different analytical strategies based on DANS fluorescence microscopy, from simple epifluorescence fragments visualization, to confocal microscopy and phasor approach for plastic components

| MATERIALS AND METHODS

| RESULTS

| CONCLUSIONS