From Handheld Near-Infrared Spectroscopy to Submicron IR (O-PTIR) and Raman Micro-spectroscopy: Multiscale Analysis of Microplastics in Soil

Soil contamination by microplastics is an increasing environmental concern with implications for ecosystem function, agriculture, and food safety. Characterizing microplastics across size scales, from millimeters to submicron particles, is essential for understanding their distribution, sources, and potential impacts. This study investigates complementary spectroscopic techniques for microplastic detection in soil, combining rapid field screening with high-resolution laboratory analysis.
Handheld near-infrared (NIR) spectroscopy has become a valuable tool not only for rapid, non-destructive and on-site analysis of materials and food, but also for the screening of microplastics in soil samples. In recent studies, we have demonstrated that this technique allows in-situ identification and quantification of common polymer types up to concentrations above 1000 ppm and provides a cost-effective means of soil monitoring.
For smaller particles and lower concentrations, optical photothermal infrared (O-PTIR) micro-spectroscopy enables infrared (IR) analysis at the sub-micron level while simultaneously acquiring Raman spectra, providing both high spatial resolution and chemical specificity. O-PTIR combines IR absorption and thermal expansion detection, allowing label-free, non-contact submicron chemical imaging of microplastics within complex soil matrices. In addition, the simultaneous acquisition of Raman spectra with O-PTIR provides complementary molecular fingerprinting at the same submicron spatial resolution, enhancing microplastic identification in complex soil environments.
By integrating handheld NIR with O-PTIR and simultaneous Raman micro-spectroscopy, a two-step multiscale workflow is established that links large-area screening to detailed chemical imaging. The advantages, limitations, and synergies of this approach are discussed, highlighting its potential for environmental monitoring, soil health assessment, and future microplastic research.