Azo-Enhanced Raman Scattering for Enhancing the Sensitivity and Tuning the Frequency of Molecular Vibrations

Area of Science:

• Chemical Physics
• Spectroscopy
• Materials Science

Background:

• Raman scattering offers stable, narrow-banded signals ideal for multicolor microscopic imaging.
• Low sensitivity due to small Raman scattering cross-sections limits current applications in Raman spectroscopy and microscopy.

Purpose of the Study:

• To introduce a novel concept, azo-enhanced Raman scattering (AERS), to overcome the sensitivity limitations of Raman spectroscopy.
• To design intrinsic molecular structures that enhance Raman signals and enable multicolor imaging with improved sensitivity.

Main Methods:

• Development of AERS molecules by integrating azobenzene units with specific vibrational modes.
• Utilizing resonance Raman and fluorescence quenching strategies to enhance Raman signal intensity and purity.
• Spectral characterization and molecular simulations to elucidate the enhancement mechanisms.

Main Results:

• AERS molecules demonstrated Raman signal enhancements exceeding 4 orders of magnitude compared to 5-ethynyl-2'-deoxyuridine (EdU).
• Azobenzene conjugation extended conjugation, coupled electronic-vibrational transitions, and improved vibrational mode symmetry, enhancing Raman signals.
• Nonradiative decay in azobenzene effectively quenched fluorescence, providing a clean background for Raman signal detection and achieving frequency tunability across 10 distinct bands.

Conclusions:

• AERS methodology enables the design of small-molecule Raman probes for multicolor spontaneous Raman imaging in complex systems.
• This approach significantly enhances Raman signal sensitivity and spectral purity, opening new avenues for interdisciplinary research and applications.