03 January 2020, a research paper by Prof. Liang Luo’ and Prof. Fanling Meng’ group entitled “Polydiacetylene-based ultrastrong bioorthogonal Raman probes for targeted live-cell Raman imaging”has been published in Nature Communications.
Raman scattering-based vibrational microscopy has been considered one of the most promising and powerful cell imaging tools in recent years, attributed to the many intriguing features it holds. However, in comparison with other widely applied imaging techniques, especially fluorescence imaging, one of the major obstacles in practicing Raman microscopy in the biological sciences is the intrinsically poor cross-section of Raman scattering of either cellulous components or vibrational probes. Raman reporters with inherent strong Raman scattering intensity are urgently needed to enable facile Raman imaging with high imaging quality.
Polydiacetylenes, a class of conjugated polymers with an alternating ene-yne backbone structure, naturally emerge as promising Raman probe candidates, given their inherently ultrastrong Raman signals originating from the large π-conjugation and polarizability of the all-planar polymer backbones. However, most polydiacetylenes are insoluble in common solvents, since they are typically prepared via topological polymerization in solid state. In addition, to achieve successful polymerization, bulky side groups with strong inter-side chain interactions are often introduced. The poor processibility and functionalizability of polydiacetylenes greatly limit their potential application in biological Raman imaging.
To address the above problems of polydiacetylenes, Prof.Luo group have developed host-guest supramolecular scaffolding strategy, which is a powerful tool for functional polydiacetylene synthesis. With the help of the self-assembly of a host molecule, non-polymerizable diacetylene monomers can be properly aligned and successfully polymerized.
Figure. A water soluble polydiacetylene Raman probe with enhanced Raman signal in the silent region which can be functionalised for organelle targeting and demonstrate application.
In this work, we have designed and synthesize a water-soluble and functionalizable polydiacetylene poly(deca-4,6-diynedioic acid) (PDDA) using the host-guest supramolecular scaffolding strategy. Compare with conventional small molecule alkyne reporters, we observe an up to ~104-fold enhancement of alkyne Raman signals of PDDA, making it an ultrastrong intrinsic alkyne Raman reporter. More strikingly, PDDA is water soluble, and its propionic acid side chains allow facile and controllable side chain engineering of the polymer as a platform for a series of Raman probes . As a proof of concept, PDDA has been functionalized with subcellular organelle targeting groups, either small molecules or peptides. Based on these PDDA derivatives, we have achieved hyperspectral live-cell Raman imaging of subcellular organelles with high spatiotemporal resolution at a low laser power and time constant.
Prof. Liang Luo, Prof. Ping Wang and Prof. Fanling Meng from Huazhong University of Science and Technology, and Prof. Joseph W. Lauher from Stony Brook University are the co-corresponding authors. Postdoctoral fellow Sidan Tian, PhD candidates Haozheng Li from Huazhong University of Science and Technology, and Dr. Zhong Li from Stony Brook University are co-first authors. This work is supported by the National Basic Research Plan of China, the National Natural Science Foundation of China, Postdoctoral Research Foundation of China, the National Science Foundation and Huazhong University Start-up Fund.