Scientists from Tomsk Polytechnic University together with Russian and Chinese colleagues have found a simple way to make the most powerful optical microscopes – nanoscopes – even more sharp-sighted. For this purpose, they proposed using nanohole-structured microspheres. Light is focused in the nanohole. It plays the role of a kind of additional lens due to which the resolution increases. Modeling and computing showed that it is thus possible to increase the resolution by at least 10 times while traditional nanoscopes allow seeing objects in the size of up to 50 nanometers. The study results were published in the journal Nanomaterials (IF: 3.5; Q1).
The resolution of conventional optical microscopes is limited by the wavelength of light. In fact, it is almost impossible to see objects smaller than 200 nanometers. There are more powerful electron microscopes, however living objects, for example, living viruses, could not be seen through them. Electron beam used in them immediately kills all living things. That’s why the increase of the resolution of optical microscopes is very important to study living objects.
In 2011, the next-generation microscopes – nanoscopes – were proposed. Scientists added a small sphere of quartz glass in the design of the microscope. It helps to improve images which are then increased by a common lens of the microscope.
The principle of nanoscopes is based on the ‘photonic jet’ effect, i.e. it is a focus that is formed at the surface of the sphere which itself is in the focus of the lens. This ‘photonic jet’ allowed increasing the resolution and eventually became a stumbling block for finding ways for further resolution increase.
The project leader, SRF of the Division of Electronic Engineering, DSc Igor Minin says:
‘To increase the resolution you need to reduce the transverse size of the jet. Some physics laws do not allow making this less than a certain value. To solve the challenge the scientists from different countries were proposing their solutions but all they did not ensure any fundamental increase in resolution. We overcame this situation as follows: in the microsphere, we made a nanohole in the size less than a wavelength and electromagnetic field started to localized in it. Therefore, in this case in the vicinity of the sphere surface the resolution will be determined by the diameter of the nanohole.’
Such nanohole provides an effect of another microlens. Moreover, with this approach the resolution does not depends on the lenses of the microscope but on the size of the nanohole in the microsphere.The smaller it is, the higher the resolution.
‘Therefore, theoretically, it is possible to increase the resolution even more. Modeling and computing allowed us to show that the resolution can be improved up to the value dozens time less than a wavelength,’ notes Igor Minin.
In the future with the help of nanoscopes having such resolution it will be possible to see, for example, the structure of a virus. Further experiments should define the limits of resolution increase.
‘Such microspheres with nanoholes are of interest not only for optical microscopy but also for nanolithography, optical traps, nanomodification of materials and other fields,’ says the researcher.
The study was conducted in cooperation with scientists from Tomsk State University (Russia), College of Computer Science and Technology, Jilin University (China), and Changchun Institute of Optics, Fine Mechanics and Physics (China).