Raman Tweezers as a Tool for Small Microplastics and Nanoplastics Identification in Sea Water

Abstract

Our understanding of the fate and distribution of micro- and nano- plastics in the marine environment and their impact on the biota compartment is limited by the intrinsic difficulties of conventional analytical techniques (light scattering, FT-IR, Raman, optical and electron microscopies) in the detection, quantification and chemical identification of small particles in liquid samples. Here we propose the use of optical tweezers, a technique awarded in 2018 with the Nobel prize, as an analytical tool for the study of micro- and nano- plastics in sea water. In particular, we exploit the combination of optical tweezers with Raman spectroscopy (Raman Tweezers, RTs) to optically trap plastic particles with sizes from tens of µm down to 90 nm and unambiguously reveal their chemical composition. RTs applications are shown on particles made of the most common plastic pollutants, including polyethylene, polypropylene, nylon and polystyrene, that are artificially fragmented and aged directly in seawater. RTs allow us to assess the size and shapes of microparticles (beads, fragments, fibers) and can be applied to investigate particles covered with organic layers. Furthermore, operating at the single particle level, RTs enable unambiguous distinction of plastic particles from marine microorganisms and seawater minerals, overcoming the capacities of standard Raman spectroscopy in liquid, limited to average measurements. Coupled to suitable extraction and concentration protocols, RTs could have a strong impact in the study of the fate of micro and nanoplastics in marine environment, as well as in the understanding of the fragmentation processes on a multi-scale level.

Raman Tweezers for Tire and Road Wear Micro- and Nanoparticles analysis

“…In this case a calibration curve of the Raman signal vs particle radius on model particles is needed. 46 Optical forces. When a particle is illuminated by a tightly focused laser beam, the exchange of linear momentum between the ray and the particle generates an optical force ⃗ = Δ B ⃗ Δ ⁄ , where Δ B ⃗ = B⃗ inc − B⃗ ref is the exchanged momentum, calculated as the difference between the incident and reflected momentum ( B⃗ inc and B ⃗ ref , respectively).…”

Response of coral reef dinoflagellates to nanoplastics under experimental conditions

“…(Clade C strain ID: NIES-4077) were isolated from Tridacna crocea and Fragum sp. in Okinawa, Japan [5]. Using glass flasks, precultures for the stress experiment were established, as previously described [4].…”

“…Small plastic particles (>1 mm) have been reported from coral islands at more than 1000 items/m 2 [4]. Further fragmentation of these particles leads to nanoplastics (<1 µm) [5]. Microplastic particles induce stress responses in scleractinian corals, suppress their immune systems and capacity to cope with environmental toxins [6].…”

“…Nanoplastics, particles smaller than 1 µm [5], can originate by fragmentation of larger plastic objects through photochemical and mechanical degradation. There are also primary sources of nanoplastics.…”

Microplastic Identification via Holographic Imaging and Machine Learning

“…Basically, common approaches to identify MPs are based on the combination of two analytical techniques, i.e., their physical characterization, using optical microscopes, followed by their chemical characterization through spectroscopy methods for assessing the plastic type . Stereomicroscopy is the most used method to identify MPs in the range 0.1–1 mm of sizes, whereas scanning electron microscopy (SEM) can identify plastic‐like particles under 0.1 mm .…”