In most cases in optics, imaging resolution is limited to roughly the wavelength of light. At the same time, the optical detection sensitivity of individual particles is theoretically unlimited. Its practical achievement is limited by the signal-to-noise ratio, where the signal represents a number of detected photons from the particle, and noise comes from unwanted photons, termed background. Therefore, the progress in individual particle imaging relies on efficiency of the background suppression. In 80-s, the efficient image processing algorithm was introduced resulting in dramatic improvement of image quality, which permitted biologists to study cellular process in vivo with great amount of details. For example, filamentous cellular structures, microtubules, sized 25-nm in diameter, were routinely imaged (Shotton, 1988) . In recent times, imaging of individual 2.5-nm gold particles has been reported (Boyer et al., 2002) pushing detection sensitivity to such a level that optical detection of macromolecules, e.g. individual proteins, may become a reality.

Figure 1. Reflection-mode DIC imaging system.

 

Figure 2. Reflection-mode DIC image of individual 55-nm diamond crystals. Scale bar, 10 micron

This PhD project aims to create a novel optical imaging system suitable for background-free imaging of nanoparticles and macromolecules. Also, we aim to study conformational dynamics of proteins using this imaging system, where conformational changes should be manifested by variation of the protein image brightness.

We have carried out preliminary research into the imaging of individual nanoparticles by building a reflection-mode differential interference contrast imaging system (DIC) in house, as shown in Figure 1. 55-nm diamond nanoparticles, previously reported in our earlier work (Colpin et al., 2006) have been successfully imaged by using this system. Refinement of the existing system should enable efficient suppression of the background resulting in detection of individual macromolecules.

REFERENCES

D. Boyer, P. Tamarat, A. Maali,B. Lounis, M. Orrit, "Photothermal imaging of nanometer-sized metal particles among scatterers" Science 297, 1160-1163 (2002).

Y. Colpin, A. Swan, A. V. Zvyagin, T. Plakhotnik, "Imaging and sizing of diamond nanoparticles", Opt. Lett. 31 , 625-627 (2006).

D. M. Shotton, "Video-enhanced light microscopy and its applications in cell biology", J. Cell Sci. 89 : 129-150 (1988). [pdf (17 Mb)]

 

For more details on this topic, visit this web-resource, or contact us.