Microplastics are a serious environmental issue. These tiny particles can be found in the oceans, freshwater, soil, living tissue, and even in the atmosphere. Due to the very slow degradation of plastics, they can accumulate in the environment and be transferred along the food chain. One approach to detecting microplastic particles is Raman spectroscopy, but single microplastic particles with sizes below 1 μm are difficult to detect due to their weak signal.

Liwu Zhang, Fudan University and Shanghai Institute of Pollution Control and Ecological Security, both Shanghai, China, and colleagues have used surfaced-enhanced Raman spectroscopy (SERS) with the commercial SERS substrate Klarite for the detection of single nanoplastics. Klarite is a gold substrate and has an ordered structure with inverted-pyramid-shaped, 1.5 μm-wide pits. The team used different sizes of polystyrene (PS) and polymethyl methacrylate (PMMA) spheres as well as samples of atmospheric microplastic particles as analytes. Solutions containing the analytes were added dropwise onto the Klarite substrate and Raman spectra were collected. Silicon wafers were used as a non-SERS control substrate.

The researchers found that Klarite can enhance the signal intensity in samples with weak Raman scattering signals, which allowed them to detect PS and PMMA particles with sizes down to 360 nm. For PS, the signal was enhanced up to two orders of magnitude. The method is also suitable for the detection of micro- and nanoplastics in atmospheric aerosols. However, the Raman signal of atmospheric samples can be difficult to tell apart from the background fluorescence caused by impurities.

• Surface-Enhanced Raman Spectroscopy Facilitates the Detection of Microplastics <1 μm in the Environment,
  Guanjun Xu, Hanyun Cheng, Robin Jones, Yiqing Feng, Kedong Gong, Kejian Li, Xiaozhong Fang, Muhammad Ali Tahir, Ventsislav Kolev Valev, Liwu Zhang,
  Environ. Sci. Technol. 2020.
  https://doi.org/10.1021/acs.est.0c02317