Infrared Photothermal Heterodyne Imaging for the Characterization of Micro- and Nanoplastic Environmental Contaminants

This dissertation explores the use of Infrared Photothermal Heterodyne Imaging (IR-PHI) in characterizing Micro and Nanoplastics (MNPs) as environmental contaminants. It begins by examining the environmental and health challenges posed by MNPs, defining their origin and distinguishing between primary and secondary types. The global prevalence of MNPs and their ecotoxicological impact, along with concerns about their effects on human health, are highlighted. The introductory chapter also reviews the detection and characterization of MNPs, discussing their physical and chemical properties, current analytical tools, and the limitations of existing techniques. It introduces IR-PHI as an emerging method that could overcome some of these limitations, offering a more integrated and accurate approach to MNP analysis. The second chapter delves into the development of IR-PHI, from its conceptual origins to its practical applications in various fields. It focuses on the use of IR-PHI in identifying and analyzing MNPs, presenting case studies like the analysis of MNPs from nylon tea bags and other environmental samples. The challenges of IR-PHI, such as slow imaging speed, are discussed, along with the future development of widefield IR-PHI (wIR-PHI) for more efficient environmental analysis. The third chapter discusses the advancement of wIR-PHI, a technique that addresses the slow imaging speed of traditional IR-PHI through synchronized nanosecond pump pulses and a high-speed complementary metal–oxide–semiconductor (CMOS) camera. This enables rapid, large-area mid-infrared photothermal image acquisition. The chapter demonstrates wIR-PHI's capabilities in fast IR imaging of individual nanoparticles, establishing a new benchmark in detection sensitivity and temporal resolution. The fourth chapter emphasizes the transformative role of IR-PHI and wIR-PHI in environmental science, particularly in monitoring MNPs. It discusses the applications of these techniques in analyzing various materials and products, highlighting the need for increased regulatory attention and public awareness. The chapter concludes by stressing the importance of understanding and addressing MNP contamination, particularly among influential communities, to drive meaningful environmental change.