The optical microscope is a well-developed scientific tool that has been successfully used in most scientific discoveries for several. As many technological breakthroughs and developments have lead to increasingly capable and advanced microscope designs that are available today, optical microscopes remain limited in regards to the presence of a light diffraction limit present within the microscope1.
Otherwise known as a microscope’s diffraction barrier, this challenge often restricts the ability of the optical instrument to distinguish between two objects that appear next to each other under the microscope, which could significantly affect the way in which scientific results are interpreted following their analysis.
The diffraction of light can be described as an event that occurs following the passing of a light wave through an opening, slit or transparent medium, such as a lens of a microscope, that subsequently appears smaller than the light’s actual wavelength2.
Under the microscope, biological samples will often exhibit highly overlapping features, which is one of the leading reasons as to why light diffraction will occur in this setting. Microscopes employ a resolution property that is directly proportional to the size of its object to be observed, while simultaneously remaining inversely proportional to the wavelength that of the emitted light.
This resolution is not controlled by the quality of the instrument, but rather by the wavelength of the light that is being employed. Due to the inability of a microscope to resolve two objects that are closer than λ/2NA from each other, in which λ describes the wavelength of the emitted light and NA is the numerical aperture of the imaging lens, light diffraction is a limiting factor in most optical microscopes3.
Due to this diffraction of light, the perceived image is often an inaccurate representation of the actual details present within the specimen as a result of the lower limit in which the microscope is capable of resolving these structural details2.
In an effort to correct this damaging property of optical microscopes, a research team from the Department of Electrical and Computer Engineering at the National University of Singapore (NUS) has developed a supercritical lens that allows optical microscopes to capture real-time images in much greater detail as compared to its predecessors4.
In a completely non-invasive manner that eliminates the need for any pre-treatment of the sample or post-processing of the image, the team led by Professor Hong Mingui claim that the application of this lens can significantly benefit both semiconductor industries as well as biological research projects in the future.
Based on the concept of a planar metalens, which is a high-performance and ultra-thin lens that allows for an extraordinary modulation of delivered light, the NUS research team has developed an algorithm for their supercritical lens4.
Once this algorithm was successfully determined, it was used to fabricate the metalens through the use of a conventional laser pattern generator. By using their supercritical lens, the NUS research team found that the microscope applied with this lens demonstrated an imaging resolution of 65 nanometers (nm), which is comparable to that of typical microscopes whose resolution often ranges from 120-150 nm4.
This method of microscopy exhibited a longer working distance of 55 micrometers (mm), which allowed for the availability of additional space to handle samples in an easier method, as well as provide for more observable details of the specimen to be uncovered.
Within the semiconductor industry, the NUS research team hopes that this method of microscopy could allow for the more rapid, accurate and cost-effective detection of potential defects within the components of a conductor to be detected at an improved resolution. While current defect detection methods will require the use of a scanning electron microscope to ensure their presence, this highly specialized tool is both expensive and requires a vacuum environment in order to function.
Within the field of biology, researchers believe that both protein and cellular imaging could find an improvement in the use of this team’s novel lens4. Typical techniques for the analysis of such biological specimens often require samples to undergo a series of dyeing steps, however, this non-invasive technique could provide a much more detailed understanding and image of biological tissues that avoids these traditional treatment requirements.
- "The Diffraction Barrier in Optical Microscopy." Nikon's MicroscopyU. Web. https://www.microscopyu.com/techniques/super-resolution/the-diffraction-barrier-in-optical-microscopy.
- "Diffraction of Light." Olympus Microscopy Resource Center. Web. http://www.olympusmicro.com/primer/lightandcolor/diffraction.html.
- "The Diffraction Limits in Optical Microscopy." AZoOptics.com. 21 Aug. 2014. Web. https://www.azooptics.com/Article.aspx?ArticleID=659 .
- "Engineers Develop Novel Lens for Super-resolution Imaging." ScienceDaily. ScienceDaily, 5 Apr. 2017. Web. 10 Apr. 2017. https://www.sciencedaily.com/releases/2017/04/170405090724.htm.
- Image Credit: Shutterstock.com/pixelparticle