Photoluminescence-Based Techniques for the Detection of Micro- and Nanoplastics

Abstract

The growing numbers related to plastic pollution are impressive, with ca. 70 % of produced plastic (>350 tonnes/year) being indiscriminately wasted in the environment. The most dangerous forms of plastic pollution for biota and human health are micro- and nano-plastics (MNPs), which are ubiquitous and more bioavailable. Their elimination is extremely difficult, but the first challenge is their detection since existing protocols are unsatisfactory for microplastics and mostly absent for nanoplastics. After a discussion of the state of the art for MNPs detection, we specifically revise the techniques based on photoluminescence that represent very promising solutions for this problem. In this context, Nile Red staining is the most used strategy and we show here its pros and limitations, but we also discuss other more recent approaches, such as the use of fluorogenic probes based on perylene-bisimide and on fluorogenic hyaluronan nanogels, with the added values of biocompatibility and water solubility.

Keywords: dye staining; luminescence; microplastics and nanoplastics; plastic pollution; sensors.

Figure 1

Global plastic production and global trends in millions of tonnes. Image available at https://www.grida.no/resources/6923. Year 2018. Credit: Maphoto/Riccardo Pravettoni. Data source: M. Bergmann, L. Gutow, M. Klage (eds) Marine Anthropogenic Litter (2015) Springer.

Figure 2

Examples of plastic stained with Nile Red in hexane, with different relative intensities in different emission channels owing to the solvatochromic properties of Nile Red. Reproduced with permission from Ref. [76]. Copyright 2020, MDPI.

Scheme 1

Molecular structure of Nile red and of three derivates.

Figure 3

Comparison of fluorescence from Nile Red stained HDPE (a), PC (b), PU (c), PEVA (d), PVC (e) and PE (f) polyester and non‐stained fibres of polyester (g), PET (h) and polyamide (i). Reproduced with permission from Ref. [59]. Copyright 2016, Elsevier.

Figure 4

Normalized emission spectra and photos of PE, PP, PET and PVC, stained with 20 μg/mL of Nile Red in acetone and ethanol at 50 °C for 10 min., showing the different emission colour due to the solvatochromism of the probe. Reproduced with permission from Ref. [87]. Copyright 2020, Elsevier.

Scheme 2

Molecular structure of hyaluronan functionalized with Rhodamine B.

Scheme 3

Molecular structure of POSS used in ref. [93].

Scheme 4

Molecular structure of the fluorogenic probe PDI.