Attenuated Total Reflection—Fourier Transform Infrared Imaging of Large Areas Using Inverted Prism Crystals and Combining Imaging and Mapping

Abstract

Attenuated total reflection-Fourier transform infrared (ATR-FT-IR) imaging is a very useful tool for capturing chemical images of various materials due to the simple sample preparation and the ability to measure wet samples or samples in an aqueous environment. However, the size of the array detector used for image acquisition is often limited and there is usually a trade off between spatial resolution and the field of view (FOV). The combination of mapping and imaging can be used to acquire images with a larger FOV without sacrificing spatial resolution. Previous attempts have demonstrated this using an infrared microscope and a Germanium hemispherical ATR crystal to achieve images of up to 2.5 mm x 2.5 mm but with varying spatial resolution and depth of penetration across the imaged area. In this paper, we demonstrate a combination of mapping and imaging with a different approach using an external optics housing for large ATR accessories and inverted ATR prisms to achieve ATR-FT-IR images with a large FOV and reasonable spatial resolution. The results have shown that a FOV of 10 mm x 14 mm can be obtained with a spatial resolution of approximately 40-60 microm when using an accessory that gives no magnification. A FOV of 1.3 mm x 1.3 mm can be obtained with spatial resolution of approximately 15-20 microm when using a diamond ATR imaging accessory with 4x magnification. No significant change in image quality such as spatial resolution or depth of penetration has been observed across the whole FOV with this method and the measurement time was approximately 15 minutes for an image consisting of 16 image tiles.

Applications of FTIR Spectroscopic Imaging in Pharmaceutical Science

“…Recent developments in the area of ATR-FTIR imaging with a variable angle of incidence opens up the opportunity of 3D imaging surface layers of skin in studies of transdermal drug delivery [10] or thin layers of polymeric or pharmaceutical samples [89]. The combination of macro-ATR imaging with mapping [90] offers possibility of obtaining images with large fields of view that may be useful in pharmaceutical analysis. The capabilities of ATR-FTIR imaging are further enhanced by the fact that it is not by necessity a destructive technique, so once a sample has been analyzed in situ it can be extracted and reanalyzed elsewhere allowing complementary techniques to be applied to further improve the investigation of a sample.…”

Collection and detection of latent fingermarks contaminated with cosmetics on nonporous and porous surfaces

“…[9] Future investigations will focus on the development of lifting materials that present less absorption in the mid-infrared region; also, the collection and study of latent fingerprints left on porous surfaces require further efforts. Studies on potential chemical information related to the suspect and hidden within the infrared spectra of latent fingerprints collected with the aid of tapes are in progress, which may eventually lead to adoption of ATR-FTIR imaging as a valuable tool for routine forensic investigations.…”

“…Obtaining FTIR images with FPA detectors in ATR mode has been successfully achieved for micro-and macro-imaging. [8,9] Other analytical techniques have also been used to study latent fingerprints; while Raman spectroscopy is a nondestructive and chemically specific approach, it was challenging to locate a substance in the fingerprint from which to obtain a Raman spectrum [10] without the chemical imaging capability of a method such as ATR-FTIR imaging. Time-of-flight secondary ion mass spectrometry is a very sensitive technique to detect residues left on a fingerprint [11] and it can be used as a complementary technique to a nondestructive and fast ATR-FTIR spectroscopic imaging approach which is applicable to a broad range of surfaces.…”

High-definition Fourier Transform Infrared (FT-IR) Spectroscopic Imaging of Human Tissue Sections towards Improving Pathology

“…In addition, FT-IR provides a novel route to obtaining additional biochemical information that may not be readily accessible using conventional staining techniques. , with many very exciting studies showing its applications [19][20][21][22][23][24][25] . In addition, it was recently demonstrated that the increased spatial resolution associated with ATR imaging can allow for the visualization and classification of endothelial and myoepithelial cells in breast tissue which form a key component of breast cancer diagnosis 26 .…”