Overcoming resolution limitations: Spectroscopy of sub-30 nm nanoplastics

Microscopic plastic particles, prevalent throughout most earthly environments, tend to break down into even smaller nanoplastic particles (NPLs). Despite the growing presence of these nanopollutants, and their potential to interact with organisms at the subcellular level – posing mostly still unknown risks – research on this topic is limited due to the absence of dependable techniques for characterizing nanoparticles. While technologies like transmission/scanning electron microscopy (TEM/SEM) or atomic force microscopy (AFM) can measure NPL geometry, standard spectroscopic techniques used for chemical characterization of microplastics, like Fourier-Transform Infrared Spectroscopy (FTIR) and micro-Raman spectroscopy (MRS), lack the resolution to analyze NPL samples exhibiting weak signals. These samples are also invisible under the coupled microscope due to their size being below the diffraction limit. We propose a novel multi-technique approach, combining standard micro-Raman spectroscopy with standard atomic force microscopy, for characterizing nanoplastics down to a size of 30 nanometers. We successfully obtained single-particle spectra from polystyrene nanoparticles as small as 25 nm, achieving a mass detection limit of 8.6 ag (attograms). This demonstrates the possibility of acquiring a clear Raman signal from a single, small nanoparticle with a resolution comparable to more intricate and time-consuming techniques like Tip-Enhanced Raman Spectroscopy and Photo-Induced Force Microscopy. These techniques, to our knowledge, have yet failed to detect NPLs of this size. Any readily implementable techniques for individual characterization of nanoparticles, using existing capabilities of laboratories worldwide, are welcome. Our combined MRS and AFM approach facilitates NP identification using standard Raman equipment available in most laboratories worldwide. Also see: https://micro2024.sciencesconf.org/551630/document