Imaging and Identification of Single Nanoplastic Particles and Agglomerates

TL;DR

The study tackles the challenge of quantifying nanoplastic pollution by enabling imaging and identification of single nanoplastic particles down to 100 nm using surface-enhanced Raman scattering (SERS). By employing a nano-patterned gold SERS substrate and a confocal microscope with dual detection paths, the authors achieve Raman signal enhancements exceeding $10^3$ for single particles and dramatically increase imaging speed via bandpass-filtered Raman imaging, achieving up to ~$10^7$-fold faster spatial detection than conventional Raman. They demonstrate that single 100 nm nanoplastics, as well as agglomerates, can be visualized with high contrast, while smaller particles show reduced signal-to-background due to illumination coverage. The approach provides a critical step toward sensitive, in-situ nanoplastic sensors in environmental monitoring, enabling precise detection independent of concentration and facilitating future sensor development.

Abstract

Currently the extent of nanoplastic in the environment can only be estimated by extrapolation from the plastic waste that can be detected. To be able to quantify the whole extent of the problem, detection methods have to be developed that can also identify particles that are smaller than 1 $μ$m. Here we employ surface-enhanced Raman scattering (SERS) to image and identify single nanoplastic particles down to 100 nm in size. We obtain an experimental enhancement factor of more than three orders of magnitude measured on a single plastic particle instead of averaging over a concentration. Our results contribute to the better understanding and employment of SERS for nanoparticle detection and present an important step for the development of future sensors.

Figures (5)

• Figure 1: Sketch of SERS substrate with polystyrene beads (left) and scanning electron microscope image of SERS substrate used for the detection of nanoplastic (right).
• Figure 2: Agglomerates of and single 300 nm PS particles on the SERS substrate visualised (a) via surface-enhanced Raman imaging and (b) via recording the backscattered laser beam. (c) Raman spectra obtained from a single nanoparticle on a SERS substrate and on a (d) reference glass substrate. Two unbroadened Raman modes that are visible in both spectra are indicated via dashed lines. The insets shows the respective Raman spectra with the bandpass filter to select the brightest C-C stretch vibrational mode.
• Figure 3: Comparison of confocal images taken of 800 nm and 300 nm polystyrene particles on a glass and a SERS substrate.
• Figure 4: Measured Raman images and their corresponding fitted images for (a) the SERS substrate and (b) a glass substrate for 800 nm PS particles. On the right of these images a 2D slice at the position indicated in the respective images is plotted to further visualise the gain in absolute signal and in signal to background ratio when imaging these nanoparticles via SERS.
• Figure 5: (a) Spectrum and surface-enhanced Raman image of a 100 nm PS particle. (b) Raman image of agglomerates and single 100 nm nanoplastic particles