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Raman Spectroscopy is a versatile technique which has evolved over the past few decades for chemical as well as biological applications. The instrumentation and the statistical evaluation procedures have matured, enabling the transition from ex-vivo demonstration to in-vivo examinations. For biological samples, Raman spectroscopy is typically sensitive to concentrations of bio-molecules such as lipids, proteins, carbohydrates, and nucleic acids. Raman spectroscopy can very accurately measure relative concentrations of these molecular classes, but is poorly suited to identify specific molecules (i.e., specific proteins or DNA sequences). In the recent past integrated Raman techniques are being increasingly explored with encouraging results. Among the upcoming and promising techniques for biomedical/chemical applications are Photoacoustic Raman spectroscopic technique, Raman spectroscopy with acoustic levitation, combination of Intra-vascular ultrasound with Raman spectroscopy, and a unique triple-modality magnetic resonance imaging-photoacoustic imaging-Raman imaging combined technique among others. Photoacoustic Raman spectroscopy (PARS) uses acoustic methods to detect energy deposited in a molecule by the process of stimulated Raman scattering. By employing two ultrashort excitation laser pulses, separated in frequency by the vibrational frequency of a targeted molecule, only the specific vibrational level of the target molecules in the illuminated tissue volume is excited. This targeted optical absorption generates ultrasonic waves, referred to as stimulated Raman photoacoustic waves, which are detected using a traditional ultrasonic transducer to form an image following the design of the established photoacoustic microscopy. In Raman acoustic levitation spectroscopy (RALS), acoustic levitation enables the contactless handling of microsized samples and the Raman spectroscopy offers the advantage of a noninvasive method without complex sample preparation. RALS has been successfully applied in monitoring sample dilution and preconcentration, evaporation, crystallization, an acid–base reaction, and analytes in a surface-enhanced Raman spectroscopy colloidal suspension. Photoacoustic imaging (PAI) is a noninvasive imaging tool to visualize optical absorbing contrast agents. Due to high ultrasonic resolution and superior optical sensitivity, PAI can be used to monitor nanoparticle-mediated cancer therapy. Time-resolved scanning acoustic microscopy (TRSAM) allows for non-invasive interrogation of tissue samples with optical resolution at the micrometer scale. However, when combined with micro-Raman spectroscopy, this technique can be used to investigate tissue morphology with regard to specific biomarkers. A brief discussion on these recent and current trends would be presented.
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