Compact Optical Setup for Broadband IR Spectroscopy Helps Compensate Strong Water Absorption Revealing Secondary Structure of Proteins in Aqueous Solutions

Conventional infrared (IR) spectroscopy faces significant limitations when analyzing aqueous solutions. Water strongly absorbs light in the mid IR region, which reduces the transmitted signal intensity and dominates the detector’s dynamic range.
To overcome this challenge, we developed a method called Solvent Absorption Compensation (SAC), which pre-compensates solvent absorption through adaptive intensity control of the incident light during wavelength scanning, ensuring that the transmitted light remains nearly constant across the scanned frequency range. This adaptive spectrum control enables more efficient use of the detector's dynamic range at every wavelength, minimizing the contribution of light absorption by solvent and significantly improving the signal-to-noise ratio of the analyte. For SAC, we adopted acousto-optic modulators for rapid intensity control while wavelength scanning. Upgrades of the optical configuration and electronics allowed a low limit of detection and a broad spectral range (970–1840 cm⁻¹). However, the earlier configurations and upgrades adopted for SAC were based on a set of focusing optics and a large footprint. In this talk, I will present a new optical setup for SAC, aiming for a compact spectroscopy system.