Raman spectroscopy explores molecular structural signatures of hidden materials in depth: Universal Multiple Angle Raman Spectroscopy

Abstract

Non-invasive 3D imaging in materials and medical research involves methodologies such as X-ray imaging, MRI, fluorescence and optical coherence tomography, NIR absorption imaging, etc., providing global morphological/density/absorption changes of the hidden components. However, molecular information of such buried materials has been elusive. In this article we demonstrate observation of molecular structural information of materials hidden/buried in depth using Raman scattering. Typically, Raman spectroscopic observations are made at fixed collection angles, such as, 90°, 135°, and 180°, except in spatially offset Raman scattering (SORS) (only back scattering based collection of photons) and transmission techniques. Such specific collection angles restrict the observations of Raman signals either from or near the surface of the materials. Universal Multiple Angle Raman Spectroscopy (UMARS) presented here employs the principle of (a) penetration depth of photons and then diffuse propagation through non-absorbing media by multiple scattering and (b) detection of signals from all the observable angles.

Raman spectroscopy: techniques and applications in the life sciences

“…This sacrifices multi-layer sensitivity for complete volumetric measurement of the sample. Ramanbased tomography has also been demonstrated using slightly different approaches, which share a common feature of using multiple fibers for excitation/detection surrounding the volume of the sample [401,402].…”

Experimentally validated Raman Monte Carlo simulation for a cuboid object to obtain Raman spectroscopic signatures for hidden material

“…Interestingly, the Raman scattered light from strongly scattering media undergoes multiple scattering events, leading to randomization of the photon directions, and detecting such Raman photons from multiple angles allows one to identify substances lying deeper within such media. Thus one can, in principle, record Raman spectra of diffusely scattering samples (both solids and colloidal liquids) at all 4π angles . In this case, the collection need not be restricted to the same plane as the excitation.…”

The Future of Forensic Biology

“…The DNA technologies combined with next-generation sequencing methods will certainly save the time and deliver accuracy in analyzing genomic data obtained from tissues [13,57]. One of the advancement could include the use of Raman spectroscopy to determine whether a suspicious powder is explosive, eliminating the need to use bleach to destroy such substances along with potential evidence [58]. Other advancement could include use of Fourier Transform Infrared (FTIR) spectroscopy to identify drugs such as cocaine in short span of time which could replace several heavy equipments that require various gases, liquids, and solids [59].…”