Fourier transform infrared spectroscopic imaging: An emerging label-free approach for molecular imaging

Fourier transform infrared (FT-IR) spectroscopy is a widely used technique for measuring the chemical composition of a sample. Dierent functional groups in molecules have resonant frequencies in the mid-IR spectral range and will absorb light corresponding to their resonant frequencies. e absorption spectrum of a molecule, hence, acts as its chemical signature and will contain contributions from each of the dierent functional groups constituting the molecule. Even when a mixture of complex composition is used, the chemically specic spectrum is oen termed a “molecular ngerprint” of the material. While the practice of FT-IR spectroscopy is over 100 years old, there has been a recent renaissance in theoretical understanding, instrumentation, and applications that has generated considerable interest in scientic study and applications in this area. In particular, the ability to couple IR spectroscopy with microscopy has been advanced signicantly with the development of array detectors. is combination of spectroscopy, microscopy, and multichannel detection is oen referred to as FT-IR spectroscopic imaging (Bhargava and Levin 2001) or FT-IR imaging. Since the primary contrast mechanism in FT-IR imaging is intrinsic, molecular, and quantitative, it alleviates the need for external contrast agents or chemicals. Consequently, FT-IR imaging has found a wide variety of applications in forensics, cancer histopathology, polymer science, drug diusion studies, art restoration, and tissue engineering. e fundamentals of instrumentation, theory, and applications will be presented in this work.