Spatial Heterodyne Offset Raman Spectroscopy Enabling Rapid, High Sensitivity Characterization of Materials' Interfaces

Fundamentals and Applications of Raman-Based Techniques for the Design and Development of Active Biomedical Materials

Raman spectroscopy is an analytical method based on light-matter interactions that can interrogate the vibrational modes of matter and provide representative molecular fingerprints. Mediated by its label-free, non-invasive nature, and high molecular specificity, Raman-based techniques have become ubiquitous tools for in situ characterization of materials. This review comprehensively describes the theoretical and practical background of Raman spectroscopy and its advanced variants. The numerous facets of material characterization that Raman scattering can reveal, including biomolecular identification, solid-to-solid phase transitions, and spatial mapping of biomolecular species in bioactive materials, are highlighted. The review illustrates the potential of these techniques in the context of active biomedical material design and development by highlighting representative studies from the literature. These studies cover the use of Raman spectroscopy for the characterization of both natural and synthetic biomaterials, including engineered tissue constructs, biopolymer systems, ceramics, and nanoparticle formulations, among others. To increase the accessibility and adoption of these techniques, the present review also provides the reader with practical recommendations on the integration of Raman techniques into the experimental laboratory toolbox. Finally, perspectives on how recent developments in plasmon- and coherently-enhanced Raman spectroscopy can propel Raman from underutilized to critical for biomaterial development are provided.

Optical system design of a DMD-SHS combined modulation interference spectrometer

Digital micromirror device (DMD) and spatial heterodyne spectroscopy (SHS) combined modulation interference spectroscopy (DMD-SHS) introduces a DMD for the secondary modulation of interferometric data to achieve a Hadamard transform. DMD-SHS can improve the performance index of the spectrometer in terms of the SNR, dynamic range, and spectral bandwidth, while retaining the advantages of a conventional SHS. The DMD-SHS optical system is more complex than a traditional SHS, which places more demands on the optical system's spatial layout and the optical components' performance. According to the DMD-SHS modulation mechanism, the functions of the main components were analyzed, and their design requirements were determined. Based on the potassium spectra detection, a DMD-SHS experimental device was designed. The potassium lamp and integrating sphere detection experiments demonstrated the detection capability of the DMD-SHS experimental device with a spectral resolution of 0.0327 nm and a spectral range of 763.66∼771.25n m, which thoroughly verified the feasibility of DMD and SHS combined modulation interference spectroscopy.

Tracking Molecular Diffusion across Biomaterials' Interfaces Using Stimulated Raman Scattering

The determination of molecular diffusion across biomaterial interfaces, including those involving hydrogels and tissues remains important, underpinning the understanding of a broad range of processes including, for example, drug delivery. Current techniques using Raman spectroscopy have previously been established as a method to quantify diffusion coefficients, although when using spontaneous Raman spectroscopy, the signal can be weak and dominated by interferences such as background fluorescence (including biological autofluoresence). To overcome these issues, we demonstrate the use of the stimulated Raman scattering technique to obtain measurements in soft tissue samples that have good signal-to-noise ratios and are largely free from fluorescence interference. As a model illustration of a small metabolite/drug molecule being transported through tissue, we use deuterated (d⁷-) glucose and monitor the Raman C-D band in a spectroscopic region free from other Raman bands. The results show that although mass transport follows a diffusion process characterized by Fick's laws within hydrogel matrices, more complex mechanisms appear within tissues.