Near-Infrared Acousto-Optic Filtered Spectroscopic Microscopy: A Solid-State Approach to Chemical Imaging

A new instrumental approach for performing spectroscopic imaging microscopy is described. The instrument integrates an acousto-optic tunable filter (AOTF) and charge-coupled-device (CCD) detector with an infinity-corrected microscope for operation in the visible and near-infrared (NIR) spectral regions. Images at moderate spectral resolution (2 nm) and high spatial resolution (1 μim) can be collected rapidly. Data are presented containing 128 × 128 pixels, although images with significantly larger formats can be collected in approximately the same time. In operation, the CCD is used as a true imaging detector, while wavelength selectivity is provided by using the AOTF and quartz tungsten halogen lamp to create a tunable source. The instrument is entirely solid state, containing no moving parts, and can be readily configured for both absorption and reflectance spectroscopies. We present visible absorption spectral images of human epithelial cells, as well as NIR vibrational absorption images of a hydrated phospholipid suspension, to demonstrate the potential of the technique in the study of biological materials. Extensions and future applications of this work are discussed.