Jaewan Park
Jihee Hwang
Sight plays a crucial role when we recognize the environment in nature. Therefore collecting the information that gives the images of the targets is essential to understand their own properties. Although many objectives can be observed without any special devices, some objectives with hundreds of micrometers or even smaller sizes cannot be observed by naked eyes. For this reason, people use special techniques called ‘microscopy’ to observe the small objectives and to obtain the information about them.

There are three types of microscopy including electron microscopy (EM), scanning probe microscopy (SPM), and fluorescence microscopy. EM and SPM provide structural information of the targets in detail via images with a high resolution (~10-10m). Despite the advantage of a high resolution, they cannot be directly applied to the biological researches because EM uses the intense electron beam which can damage the live cells, and SPM does not supplies the information of the interior of the objective, but the surface. Fluorescence microscopy has a relatively poor resolution (~10-7m) which results from the diffraction of light. However, it can bring the image of the interior of living cell with molecular specificity. Because of these advantages, fluorescence microscopy is widely used to investigate the biological problems.

The fluorescence microscopy system in our lab is based on the confocal microscopy which provides the diffraction limited resolution. The basic principle of fluorescence microscopy is observing the labeled fluorophores on the sample by illuminating. In confocal microscopy, a pinhole in front of the detector efficiently blocks the background signals came from the non-focal planes (Figure 1-a). As a result, the signal-to-noise ratio is increased and the resolution of confocal microscopy is closed to the diffraction limit (Figure 1-b).

Figure 1 (a) Schematic diagram of our confocal microscopy setup. (b) Confocal image of 50nm fluorescence nano diamond (FND). (c) Time-resolved fluorescence intensity measurement using acousto-optic tunable filter (AOTF). (d) Cross-correlation of fluorescence intensity fluctuation of Cy3 in water.

Our team built the setup for fluorescence microscopy. As a result, the accessibility of our setup is a significant advantage to apply to various researches compared to a conventional microscope. Furthermore, we try to add some spectroscopy technique on the microscopy setup. For example, we added the acousto-optic tunable filter (AOTF) to the pump-probe techniques, and correlator to the fluorescence correlation spectroscopy, respectively. Thus we can obtain not only the image of the sample but also the photo-physical information (Figure 1-c, 1-d).

Our team investigates the properties of various fluorophores and develops a new method to break the diffraction limit of a far-field optical microscope. We are especially interested in the photo-switchable nature of carbocyanine dyes such as Cy5 and Alexa647, which are widely used to image the biomolecules. We try to overcome the disadvantages of some super-resolution microscopy techniques by using these photo-switchable characters of carbocyanine dyes.
Single Molecule Spectroscopy
Super-resolution Optical & Nano-optical Nanoscopy
Real-time Femtosecond Dynamics