Abstract
Raman scattering provides stable narrow-banded signals that potentially allow for multicolor microscopic imaging. The major obstacle for the applications of Raman spectroscopy and microscopy is the small cross section of Raman scattering that results in low sensitivity. Here, we report a new concept of azo-enhanced Raman scattering (AERS) by designing the intrinsic molecular structures using resonance Raman and concomitant fluorescence quenching strategies. Based on the selection of vibrational modes and the enhancing unit of azobenzenes, we obtained a library of AERS molecules with specific Raman signals in the fingerprint and silent frequency regions. The spectral characterization and molecular simulation revealed that the azobenzene unit conjugated to the vibrational modes significantly enhanced Raman signals due to the mechanism of extending the conjugation system, coupling the electronic–vibrational transitions, and improving the symmetry of vibrational modes. The nonradiative decay of azobenzene from the excited state quenched the commitment fluorescence, thus providing a clean background for identifying Raman scattering. The most sensitive AERS molecules produced Raman signals of more than 4 orders of magnitude compared to 5-ethynyl-2′-deoxyuridine (EdU). In addition, a frequency tunability of 10 distinct Raman bands was achieved by selecting different types of vibrational modes. This methodology of AERS allows for designing small-molecule Raman probes to visualize various entities in complex systems by multicolor spontaneous Raman imaging. It will open new prospects to explore innovative applications of AERS in interdisciplinary research fields.
Highlights
The intrinsic nature of molecular vibrations enables narrow bands and stable intensities of Raman scattering when the vibrations are coupled with incident light
Since the initial demonstration of cellular Raman imaging based on 5-ethynyl-2′-deoxyuridine (EdU),[34] numerous alkyne-containing molecules have been exploited to provide strong Raman signals.[35−40] The improved structures of phenylcapped or polydiacetylene-based polyynes were synthesized for stimulated Raman scattering (SRS) imaging, while the former ones were demonstrated as Received: January 23, 2021
To achieve azocell encoding applications using AERS probes and spontaneous enhanced Raman scattering, we explored the feasibility of
Summary
The intrinsic nature of molecular vibrations enables narrow bands and stable intensities of Raman scattering when the vibrations are coupled with incident light This feature provides a significant advantage for multicolor microscopic imaging and supercapacity information encoding using Raman scattering.[1−6] the low cross section of Raman scattering places one of the major obstacles when Raman spectroscopy and imaging are applied to identify trace amounts of components in complicated systems that require ultrasensitive detection, e.g., live cells.[7−11] Many strategies and techniques, such as coherent anti-Stokes Raman scattering (CARS), stimulated Raman scattering (SRS), surfaceenhanced Raman scattering (SERS), and tip-enhanced Raman scattering (TERS), have been developed to boost Raman signals of molecules.
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