Producing biological lenses and lasers to improve microscopy
Microscopes have been around for hundreds of years and the technology behind these devices has been quickly developing over the past centuries. Microscopy has already helped us to image cells into great detail, which is essential for the identification of mechanisms behind diseases such as Alzheimer’s, of which we still don’t know the exact mechanism, but also for developing synthetic biology even further. In this age, the technology and knowledge of microscopy is no longer limiting for making detailed images of the cell; it’s the cells itself. When using fluorescence microscopy, a fluorescent cell only emits a limited number of photons, a part of this will not reach the detector. This year’s TU Delft team is using synthetic biology with the aim of improving fluorescence microscopy. There are two research lines: producing biological lenses and inventing a bacterial laser. Hover over the pictures underneath to find out more.
The goal of our biological microlenses is to increase the fraction of light captured by the detector of a microscope. Lenses are known to focus light onto a surface. By applying a layer of our biological microlenses on the detector of a microscope, we can increase the fraction of light captured. To produce microlenses, we expressed the enzyme silicatein in our cells, which catalyzes polymerization of silicic acid (Cha et al., 1999). This results in a biosilica layer around the cell (Muller et al., 2008), allowing the cell to function as a microlens. Since the shape of the lenses is a crucial property, we also overexpressed the gene bolA in our silica covered cells, which produces a round cell shape when overexpressed (Aldea & Concha, 1988), to produce round lenses. Apart from using the lenses for microscopy, we can also use the lenses for improving the efficiency of solar panels, thin lightweight cameras with high resolution or 3D screens.
By turning a cell into a biolaser, we will increase the light intensity emitted by the fluorescent cell. The cell will then emit more photons without changing the fluorophore concentration. When more photons are emitted, more photons can be detected by the microscope. A laser works by resonating photons within a closed space, in this case a cell of E. coli. We approached this by expressing fluorescent proteins within our biosilica-covered cells we used for our biolenses. When exciting the fluorophores, a fraction of the photons are trapped inside the cell by the biosilica layer. When these photons meet other excited fluorescent proteins they cause them to emit a photon with the same wavelength and direction, this process is called ‘stimulated emission’ (Einstein, A. 1917) and results in light with a higher intensity and thus more emitted photons compared to conventional fluorescence.
- Aldea, M., & Concha, H. C. (1988). Identification, Cloning, and Expression of bolA, an ftsZ-Dependent Morphogene of Escherichia coli. Journal of Bacteriology.
- Cha, J. N., Shimizu, K., Zhou, Y., Christiansen, S. C., Chmelka, B. F., Stucky, G. D., & Morse, D. E. (1999). Silicatein filaments and subunits from a marine sponge direct the polymerization of silica and silicones in vitro. Biochemistry, 96, 361–365.
- Einstein, A. (1917): "Zur Quantentheorie der Strahlung". Physikalische Zeitschrift 18, 121-128
- Muller, W., Engel, S., Wang, X., Wolf, S., Tremel, W., Thakur, N., … Schrodel, H. (2008). Bioencapsulation of living bacteria (Escherichia coli) with poly(silicate) after transformation with silicatein-α gene. Biomaterials, 29(7), 771–779. http://doi.org/10.1016/j.biomaterials.2007.10.038