How can Raman spectroscopy be used to image live cells without labels?

Raman spectroscopy is a powerful technique that can reveal the molecular composition and structure of materials by measuring the scattering of light. It can also be used to image live cells without labels, which are usually required for other imaging methods such as fluorescence microscopy. In this article, you will learn how Raman spectroscopy works, what are its advantages and limitations, and how it can be applied to study various aspects of cell biology.

1 How Raman spectroscopy works

Raman spectroscopy is based on the principle that when a beam of monochromatic light, such as a laser, hits a sample, some of the photons are scattered in different directions and wavelengths. Most of the scattered photons have the same wavelength as the incident light, which is called Rayleigh scattering. However, a small fraction of the photons lose or gain some energy and have a different wavelength, which is called Raman scattering. The amount of energy change depends on the vibrational modes of the molecules in the sample, which reflect their chemical bonds and structures. By analyzing the spectrum of Raman scattered light, one can identify the molecular composition and structure of the sample.

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Matej Krajcovic

AI for Bio/Chem, Big Pharma, PhD @ Cornell
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The AI write up about Raman spectroscopy is quite accurate. Raman spectroscopy is typically used for chemicals and not whole cells, but there are reports of it being used on whole cells. Cells consist from thousands of different molecules so the signal is quite complex. Raman scattering is also weak in energy, so they source light must be powerful and this can be detrimental to the live cell.

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2 How Raman spectroscopy images live cells

To image live cells using Raman spectroscopy, one needs to focus a laser beam on a single point of the cell and collect the Raman scattered light using a spectrometer and a detector. By scanning the laser beam over the cell, one can obtain a series of spectra from different locations, which can be used to reconstruct an image of the cell based on the intensity or the wavelength of the Raman signal. The image can reveal the distribution and concentration of various biomolecules, such as proteins, lipids, nucleic acids, and metabolites, in the cell.

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Matej Krajcovic

AI for Bio/Chem, Big Pharma, PhD @ Cornell
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A key consideration in use of Raman spectroscopy is the strength of the laser that is used on the live cells. Light with shorter wavelength will contain more energy and will be more deadly to the cells. Therefore light in the infrared spectrum is most likely most suitable.

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3 What are the advantages of Raman spectroscopy

One of the main advantages of Raman spectroscopy is that it does not require any labels, such as fluorescent dyes or antibodies, to image live cells. Labels can interfere with the normal function and behavior of the cells, or cause photobleaching and photodamage. Raman spectroscopy can also provide more information than other label-free techniques, such as phase contrast or bright field microscopy, because it can distinguish between different types of molecules based on their vibrational signatures. Moreover, Raman spectroscopy can be combined with other imaging methods, such as optical tweezers or atomic force microscopy, to manipulate and measure the mechanical properties of the cells.

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Matej Krajcovic

AI for Bio/Chem, Big Pharma, PhD @ Cornell
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The advantages listed are valid but in practice raman spectroscopy is rarely used with live cells because you need a powerful laser to elicit the weak raman scattering and therefore you will hurt the live cells. Raman spectroscopy is much more suited for chemicals.

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4 What are the limitations of Raman spectroscopy

One of the main limitations of Raman spectroscopy is that it has a low signal-to-noise ratio, which means that it requires a high-intensity laser and a long exposure time to obtain a clear image. This can increase the risk of photodamage and phototoxicity to the cells, especially at high laser powers and wavelengths. Another limitation is that Raman spectroscopy has a low spatial resolution, which means that it cannot resolve the fine details and structures of the cells, such as organelles or membranes. Furthermore, Raman spectroscopy can be affected by background signals from the culture medium, the substrate, or the water in the cells, which can mask or distort the Raman spectra.

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5 How Raman spectroscopy can be applied to cell biology

Despite its limitations, Raman spectroscopy can be applied to various aspects of cell biology, such as cell differentiation, cell cycle, cell signaling, cell metabolism, cell stress, and cell death. For example, Raman spectroscopy can be used to monitor the changes in the molecular composition and structure of the cells during their differentiation from stem cells to specific cell types, such as neurons or cardiomyocytes. Raman spectroscopy can also be used to detect the variations in the DNA and protein content of the cells during their progression through the cell cycle, or the alterations in the lipid and metabolite profiles of the cells in response to external stimuli, such as drugs or toxins. Additionally, Raman spectroscopy can be used to identify the markers and mechanisms of cell stress and cell death, such as oxidative stress, apoptosis, necrosis, or autophagy.

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Matej Krajcovic

AI for Bio/Chem, Big Pharma, PhD @ Cornell
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The biggest advantage of Raman spectroscopy is that it does not require any labeling of the cells and therefore it can be used with primary cells (cells isolated directly from an animal).

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6 How to learn more about Raman spectroscopy

If you are interested in learning more about Raman spectroscopy and its applications to cell biology, you can find many online resources, such as books, journals, websites, and videos, that can provide you with more details and examples. You can also look for courses, workshops, or webinars that can teach you the basics and the advanced aspects of Raman spectroscopy, such as the instrumentation, the data analysis, and the interpretation. You can also join online communities, forums, or networks that can connect you with other researchers and experts who can share their knowledge and experience with you.

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7 Here’s what else to consider

This is a space to share examples, stories, or insights that don’t fit into any of the previous sections. What else would you like to add?

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How can Raman spectroscopy be used to image live cells without labels?

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1 How Raman spectroscopy works

2 How Raman spectroscopy images live cells

3 What are the advantages of Raman spectroscopy

4 What are the limitations of Raman spectroscopy

5 How Raman spectroscopy can be applied to cell biology

6 How to learn more about Raman spectroscopy

7 Here’s what else to consider

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