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A tutorial on optical photothermal infrared (O-PTIR) microscopy
Summary
This tutorial reviews optical photothermal infrared microscopy, a technique that achieves up to 30 times better spatial resolution than conventional infrared imaging. Researchers describe how this method enables chemical identification of materials at the sub-micrometer scale, with applications ranging from biomedical research to microplastics detection. The technology is particularly valuable for environmental scientists who need to identify and characterize extremely small plastic particles in complex samples.
This tutorial reviews the rapidly growing field of optical photothermal infrared (O-PTIR) spectroscopy and chemical imaging. O-PTIR is an infrared super-resolution measurement technique where a shorter wavelength visible probe is used to measure and map infrared (IR) absorption with spatial resolution up to 30× better than conventional techniques such as Fourier transform infrared and direct IR laser imaging systems. This article reviews key limitations of conventional IR instruments, the O-PTIR technology breakthroughs, and their origins that have overcome the prior limitations. This article also discusses recent developments in expanding multi-modal O-PTIR approaches that enable complementary Raman spectroscopy and fluorescence microscopy imaging, including wide-field O-PTIR imaging with fluorescence-based detection of IR absorption. Various practical subjects are covered, including sample preparation techniques, optimal measurement configurations, use of IR tags/labels and techniques for data analysis, and visualization. Key O-PTIR applications are reviewed in many areas, including biological and biomedical sciences, environmental and microplastics research, (bio)pharmaceuticals, materials science, cultural heritage, forensics, photonics, and failure analysis.