Researchers at the University of Illinois' Beckman Institute for Advanced Science and Technology (Urbana, IL, USA) have created a non-invasive 3-D method for visualizing, quantifying, and studying cells without the use of fluorescence or contrast agents.
The researchers who developed the technique have used it to visualize the E. coli bacteria with a combination of speed, scale, and resolution that they claim is unparalleled for a label-free method.
The method is based on a broadband interferometric technique known as Spatial Light Interference Microscopy (SLIM) that was designed by Beckman Institute researcher Gabriel Popescu as an add-on module to a commercial phase contrast microscope.
Like all linear optical systems, the resolution of a SLIM is limited by diffraction. But by applying a novel 3-D deconvolution algorithm to retrieve sub-diffraction limited resolution information from the fields measured by SLIM, Popescu and his fellow researchers were able to render tomographic images with a resolution beyond SLIM’s diffraction limits.
They used the so-called deconvolution Spatial Light Interference Tomography (dSLIT), method to render 3-D reconstructed images of E. coli cells, enabling them to visualize the specimens at sub-cellular scales without the use of fluorescence or contrast agents.
The image above shows a comparison of a SLIM and dSLIT image of an E. coli cell. It can be seen that dSLIT reveals a helical sub-cellular structure which was not resolvable just using SLIM. The diameter of the cell is approximately 0.5 microns.
More information on the system can be found here.
-- Dave Wilson, Senior Editor, Vision Systems Design