Nanoparticles Based Nanoscopy and Super Resolution Imaging

The ability to observe structures that are on a nanometric scale is a key merit for understanding cellular functions and design effective therapies for medical applications. This seminar will present techniques to overcome the state-of-the-art limitations in microscopy. 

The resolution of a visible light microscope is limited by the phenomenon of diffraction to length scales of approximately half the wavelength of the light (~250nm). As a result, objects with smaller dimensions will appear as blurred diffraction limited spots. The ongoing aspiration is to overcome this limit in order to observe and understand the building blocks of nature. Super-resolution localization microscopy techniques have revolutionized the observation of living structures at the cellular scale, by achieving a spatial resolution that is improved by more than an order of magnitude with compared to the diffraction limit. These methods localize single events from isolated sources in repeated cycles in order to achieve super-resolution. The requirement for sparse distribution of simultaneously activated sources in the field of view, dictates the acquisition of thousands of frames in order to construct the full super-resolution image. As a result, these methods have slow temporal resolution which is a major limitation when investigating live-cell dynamics. We suggest the use of image processing techniques for fast and high density super-resolution localization microscopy.

Poor SNR conditions is another obstacle when imaging biological samples in vivo. In vivo imaging suffers from environmental conditions that yield high background noises. As a result, there is a need for noise immune microscopy setups. In my research we used gold nanoparticles as biomarkers of biological samples. We developed the temporally sequenced labeling technique, aimed for the simultaneous detection of multiple types of gold nanoparticles within a biological sample and their separation at sub-diffraction distances, using lock-in detection. 

3D microscopy is another very important task as it allows the visualization of the interior of living cells. Most of the 3D imaging techniques require long acquisition periods, thus are time consuming and not applicable for live imaging. We used phase retrieval algorithms in order to reconstruct 3D images of biological samples out of two focus planes with the goal of studying molecular-scale biological systems, thus providing valuable insights into cellular processes.

* The work was carried out towards the Ph.D. degree in the Faculty of Engineering, Bar-Ilan University, with the supervision of Prof. Zeev Zalevsky