Scientists from the University of Twente, the Netherlands, have successfully exploited the optical properties of fluorescent nanoparticles to broaden the scope of single-cell microscopy.
By using nanoparticles, they succeeded in combining two different optical microscopy techniques on the same cell. This opens exciting new possibilities for cellular imaging. Henk-Jan van Manen and Cees Otto from the Biophysical Engineering Group of the MESA+ Institute for Nanotechnology describe their results in Nano Letters.
The ‘quantum dot’ nanoparticles used by Van Manen and Otto replace existing fluorescent labels that are employed to enable the cell’s biomolecules to light up under the microscope. While fluorescence microscopy continues to be instrumental in unraveling the intricate biological processes that take place inside living cells, it would be even more informative to combine it with the intracellular chemical analysis capabilities of vibrational spectroscopy techniques such as Raman microscopy. Common fluorescent labels are not suitable for this combination, however, because the much stronger fluorescence overshadows the intrinsic weak Raman signals coming from cells. By taking fluorescent quantum dots that emit light in a wavelength region that is well-separated from Raman signals, the Dutch researchers now show that fluorescence microscopy can indeed be combined with Raman microscopy on the same cell.
Techniques based on vibrational spectroscopy are able to detect the specific vibrations that occur inside the cell’s biomolecules (such as DNA, proteins, and lipids), making them very powerful tools for ‘chemical fingerprinting’ of cells. In contrast to fluorescence microscopy, vibrational spectroscopy does not require the biomolecules of interest to be labeled, which is a great advantage. The Biophysical Engineering Group at the University of Twente, headed by prof. Vinod Subramaniam, has pioneered the application of Raman spectroscopy to investigate the chemical make-up of single cells, and this group is now worldwide at the front of high-resolution chemical mapping of cells by Raman microscopy.