Mid-Infrared Photothermal Imaging of Active Pharmaceutical Ingredients at Submicrometer Spatial Resolution.

Chemical imaging with sufficient spatial resolution to resolve microparticles in tablets is essential to ensure high quality and efficacy in controlled release. The existing modalities have the following disadvantages: they are time-consuming or have poor spatial resolution or low chemical specificity. Here, we demonstrate an epi-detected mid-infrared photothermal (epi-MIP) microscope at a spatial resolution of 0.65 μm. Providing identical spectral profiles as conventional infrared spectroscopy, our epi-MIP microscope enabled mapping of both active pharmaceutical ingredients and excipients of a drug tablet.