Mid-infrared spectroscopy and its applications in biomedical analysis and imaging

Mid-infrared (MIR) spectroscopy is an essential tool in the study of molecular structures and material compositions. It can identify chemical bonds and functional groups in molecules. Moreover, it is able to analyze the structures of biomolecules like proteins, lipids, and carbohydrates, as well as their changes under different conditions. One of its remarkable advantages lies in its non - destructiveness, high sensitivity, and high selectivity. MIR spectroscopic imaging, which makes use of the inherent vibrational contrast of molecules (e.g., Fourier-transform infrared (FTIR) spectroscopy), has emerged as a powerful analytical method for identifying and characterizing molecular samples. On the other hand, mid-infrared photothermal (MIP) microscopy uses visible light to detect the photothermal effects induced by IR absorption. This approach not only enhances the spatial resolution but also reduces the impact of water molecules on measurements. MIP microscopy provides submicron spatial resolution and depth-resolved chemical imaging capabilities, along with high spectral fidelity and a weak water background. This review will explore the principles, limitations, and technological advancements of FTIR spectroscopy and photothermal spectroscopic imaging. In addition, it will discuss their applications in biomedical analysis and imaging. By doing so, it can help evaluate the potential of MIR spectroscopy in the biomedical field and guide its further development.