Development of targeted STORM for super resolution imaging of biological samples

Microscopes are useful tools in the study of biological systems. They employ the use of optical systems principle for viewing the various specimen under investigation. To date, considerable efforts have been initiated to improve the workability of such optical system devices geared towards enhancing resolution, reducing imaging time and increasing their efficiency. As a result, methods such as stimulated emission depletion microscopy (STED) and localized microscopy among several others have been developed. They have resulted in significant improvements that have for example enabled determination of a nanoscale biological structures.

However, most of these microscopy techniques are faced with various challenges. For instance, it is difficult to image a live cell using the localized microscopy (LM) technique because it requires a high amount of optical power that results in cells photo-damage. It also affects its resolution which also depends on the photo-toxicity. To reduce a large amount of power required during the LM microscopy experiments, a good practice would be to identify and locally image the region of interests by using super-resolution method. It means that the resulting surrounding areas will be left unperturbed, thus calling for a proper and efficient illumination control system for the imaging platform.

Although several illumination control techniques are available, the most prevalent one is the spatial light modulator (SLM). SLMs devices can be further classified into liquid crystal based for phase modulation and digital mirror device (DMD) for on and off modulation.

A group of researchers at University of Sheffield in the United Kingdom: PhD student, Liyana Valiya Peedikakkal and Dr. Ashley Cadby from the Department of Physics and Astronomy in collaboration with Victoria Steventon and Professor Andrew Furley from the Department of Biomedical Sciences demonstrated a digital mirror device based simple illumination system for the localized microscopy and in particular stochastic optical reconstruction microscopy (STORM). The system was used to deliver high power densities to the identified specific imaging areas of the plane sample. Their research work is currently published in the research journal, Optics Communications.

The authors observed that the developed targeted STORM was capable of imaging a labeled cell area of a selected area without causing any photo-damage to the surrounding areas of the samples.

The application of DMD to STORM technology enables the users to select an area of interest within the field of view thereby isolating the other areas without any damages to the cells through the increased illumination powers. It is also suitable for conserving time as the isolated samples can be studied at convenient times. The choice of DMD in controlling power delivered to a particular sample was due to its high speed, large spectral range, and high contrast ratio. The system can also incorporate the use of Fourier ring correlation to measure the resolution of the image and stop when the limit is reached. Although the authors did not establish the relationship between the super-resolution radial fluctuations (SRRF) resolutions, they, however, pointed out that it depends on the power densities and hence are optimistic that it will enable sacrificial of imaging resolution with power.