Enhancing Alkyne-Based Raman Tags with a Sulfur Linker

Abstract

Alkyne-based Raman tags have proven their utility for biological imaging. Although the alkynyl stretching mode is a relatively strong Raman scatterer, the detection sensitivity of alkyne-tagged compounds is ultimately limited by the magnitude of the probe’s Raman response. In order to improve the performance of alkyne-based Raman probes, we have designed several tags that benefit from π–π conjugation as well as from additional n−π conjugation with a sulfur linker. We show that the sulfur linker provides additional enhancement and line width narrowing, offering a simple yet effective strategy for improving alkyne-based Raman tags. We validate the utility of various sulfur-linked alkyne tags for cellular imaging through stimulated Raman scattering microscopy.

Biomedical applications, perspectives and tag design concepts in the cell – silent Raman window

“…A very recent development in the SRS field is the employment of alkyne-based Raman tags with a sulfur-linker, which not only provides an 8-fold enhancement of the alkyne stretching cross-section but also retains a narrow line width of the band. 55 The suggested probes were shown to be well-tolerated by HeLa cells ( Fig. 3d ) and metabolically esterified to neutral lipids after cellular uptake.…”

“… 59 Apart from multiple alkynes, a sulfur linker can also enhance the tag signal through n–π conjugation. 55 …”

“… 59 Other tags which have been assessed in terms of stability over time in the cellular environment (through NMR assays) include sulfur-linked phenylacetylene tags. 55 …”

Unnatural Amino Acids for Biological Spectroscopy and Microscopy

“…However, for an alkyne group attached to the side chain of an amino acid, the oscillator strength of its CC stretching vibration is typically very small, making it less useful in practice as an IR probe. However, it can be used as a site-specific Raman probe of protein structure and dynamics. , In this regard, various alkyne-based Raman reporters have been developed for biological imaging via stimulated Raman scattering (SRS) microscopy . In addition, Cho and co-workers , showed that addition of a heavy atom, such as silicon (Si) or selenium (Se), between the probe alkyne group and the parent molecule can significantly enhance the transition dipole moment and the vibrational lifetime of the corresponding CC stretching vibration.…”

Triple-Bond Vibrations: Emerging Applications in Energy and Biological Sciences

“…For example, (1) Luo and co-workers showed that the CC bonds in polydiacetylene poly­(deca-4,6-diynedioic acid), which is water-soluble and functionalizable, exhibit significantly enhanced (up to ca. 10 4 fold) Raman intensity compared to conventional alkyne Raman probes and, hence, can be used for high-quality live-cell SRS imaging; (2) Potma and co-workers demonstrated that a sulfur linker can significantly improve the performance of several alkyne-based Raman probes in SRS imagining applications; (3) Fujita and co-workers utilized gold nanoparticles accumulated in the lysosome of live cells to enhance the Raman signals of colocalized alkyne-tagged drug-like molecules; (4) Ji and co-workers achieved photoswitch ability in SRS spectroscopy and microscopy by introducing alkyne-based Raman probes into the photochromic diarylethene (DTE) and demonstrated the biological utility of this technique in live cell imaging through an intracellular pulse-chase experiment; (5) Tomkinson and co-workers developed a series of low molecular weight oligoyne compounds, the alkyne stretching frequencies of which exhibit a dependence on pH, as intracellular Raman pH sensors, as well as an alkyne-based ratiometric Raman sensor for intracellular imaging of esterase activity using SRS microscopy; and (6) Evans and co-workers demonstrated the potential utility of DC473, a photosensitizer with two alkyne groups, for the study of time-dependent single-cell pharmacodynamics.…”