Identification of microplastics and nanoplastics in environmental water by AFM-IR

Microplastics and nanoplastics have gained worldwide attention as environmental hazards, and reliable analysis of these tiny particles is critical to accurate assessment of their impact to the environment and human health. Among the typical methods developed for analysis of microplastics, mass spectrometry-based methods are destructive and not applicable to individual nanoplastic particles, whereas vibrational spectroscopic techniques in combination with optical microscopy do not have sufficient spatial resolution needed for characterization of the much smaller nanoplastics. Therefore, a new tool is needed for the identification of nanoplastics in the environment.

Here we report for the first time identification of individual nanoplastics in an environmental water sample directly by atomic force microscopy-infrared (AFM-IR), a spectroscopic technique with a spatial resolution of ∼100 nm. On the basis of their spectral characteristics, four different nanoplastics, including poly(3-hydroxybutyrate) (P3HB) and a bisphenol-A based epoxy, as well as microplastics of the latter and two different polyesters were identified unambiguously, and the P3HB nanoplastic particle was found to be highly crystalline. Particles of fatty acid salt, lactic acid salt and sulfate were also identified. Amide bands were observed in the spectra of some of these particles, indicative of protein contamination. In addition, a diatom and a bacterium were identified based on their IR spectra in conjunction with the morphology and elemental composition.

This work demonstrates that AFM-IR is a powerful tool for studying individual nanoplastic particles in environmental samples, capable of providing not only their identities but also detailed structure information.