Living Single-Cell Real Time Imaging via Plasmonic-Enhanced Rayleigh & Raman Spectroscopy

Single-cell analysis is an active research area focused on deciphering cellular processes from a single living cell.¹ Various crucial biological phenomena are either invisible or only partially characterized when analyzed with standard techniques that utilize bulk cell populations or entire tissues. This is due to the high level of heterogeneity within cell cultures.^1-3 To provide novel insight into these diverse biological properties specific analytical methods capable of recording single cell measurements are much needed. Currently, major technologies include flow cytometry, fluorescent microscopy, and mass spectrometry coupled to separation techniques, such as microfluidic systems or capillary electrophoresis.^1-2  While these techniques provide valuable insight into the makeup of individual cells, they do not provide real-time dynamics data for changes throughout cellular events and are limited to the examination of a small number of genes, proteins, or metabolites¹. In addition, these methods have technique-specific limitations, for example, flow cytometry largely depends on fluorescence-based detection of dyed biomarkers which can result in biomarker structural changes and restrict temporal resolution and detection specificity.²  Using an approach that combines dark field Rayleigh scatter imaging, Rayleigh plasmon scattering, Raman scattering images, and surface-enhanced Raman spectroscopy (SERS) Kang et al. has developed a targeted plasmonically enhanced single-cell Raman/Rayleigh spectroscopy, or TPE-SCRR, technique.^4-5 These SERS-based techniques utilize rich vibrational fingerprint information, and increased sensitivity through plasmon-enhanced excitation and scattering, enabling both label and label-free detection of low concentration intracellular molecules.^{3, 6} The use of plasmonic-enhanced Rayleigh and Raman spectroscopy show immense potential for real-time imaging of cellular events, including cell division⁴, drug-response⁷, cell differentiation, nano-toxicity, and a number of other microbiology studies. 

References:

1. Wang, D.; Bodovitz, S., Single cell analysis: the new frontier in ‘omics’. Trends in Biotechnology 2010, 28 (6), 281-290.
2. Kuku, G.; Altunbek, M.; Culha, M., Surface-Enhanced Raman Scattering for Label-Free Living Single Cell Analysis. Analytical Chemistry 2017, 89 (21), 11160-11166.
3. Zong, C.; Xu, M.; Xu, L.-J.; Wei, T.; Ma, X.; Zheng, X.-S.; Hu, R.; Ren, B., Surface-Enhanced Raman Spectroscopy for Bioanalysis: Reliability and Challenges. Chemical Reviews 2018, 118 (10), 49464980.
4. Kang, B.; Austin, L. A.; El-Sayed, M. A., Real-Time Molecular Imaging throughout the Entire Cell Cycle by Targeted Plasmonic-Enhanced Rayleigh/Raman Spectroscopy. Nano Letters 2012, 12 (10), 5369-5375.
5. Kang, B.; Austin, L. A.; El-Sayed, M. A., Observing Real-Time Molecular Event Dynamics of Apoptosis in Living Cancer Cells using Nuclear-Targeted Plasmonically Enhanced Raman Nanoprobes. ACS Nano 2014, 8 (5), 4883-4892.
6. Stiles, P. L.; Dieringer, J. A.; Shah, N. C.; Van Duyne, R. P., Surface-enhanced Raman spectroscopy. Annual review of analytical chemistry (Palo Alto, Calif.) 2008, 1, 601-2
7. Austin, L. A.; Kang, B.; El-Sayed, M. A., A New Nanotechnology Technique for Determining Drug Efficacy Using Targeted Plasmonically Enhanced Single Cell Imaging Spectroscopy. Journal of the American Chemical Society 2013, 135 (12), 4688-4691.