Observations of the interior structure of cells and sub-cellular organelles are important steps in understanding cell function and its interaction with the environment. In recent years, several wide-field optical microscope techniques have been developed that allow for cells to be imaged at resolutions that break the optical diffraction limit. These super-resolution techniques are typically based on fluorescence imaging and utilize either a form of structured illumination to restrict the effective excitation volume by making use of the non linear optical properties of the flurophore molecules, or by some form of statistical image reconstruction. Each technique that has been developed has some limitation due to requirements on the laser power utilized or the temporal resolution and time required to collect an image.
Alternatively, energetic particles such as electrons and ions can be used to achieve sub-optical diffraction limit images (< 200 nm) in cells, (albeit in dried fixed cells) because the resolution is not determined by diffraction, but by the ability to focus the probe beam spot down to nanometre dimensions. For applications where whole cell imaging is desired at sub-100 nm then energetic MeV ions such as protons and alpha particles are particularly attractive as they do not spread laterally as they penetrate microns of biological material.
Whole cell imaging at sub-diffraction limit resolution - We have developed a dedicated whole cell imaging beam line at the Centre for Ion Beam Applications (CIBA), in the Physics Department. We have shown that whole cells can be imaged using Scanning Transmission Ion Microscopy (STIM) with lateral resolutions down to 25 nm. We have also done some preliminary studies into utilizing MeV protons for fluorescence imaging. The research programme is ongoing and future development include upgrading of the fluorescence imaging system and using the beam line to image nano-particle uptake into cells for drug delivery applications. Preliminary results on using nuclear microscopy for imaging gold nano-particles in cells have been successful in that we are able to quantify the number of nano-particles and establish their location within the cell.