40This diagram shows the difference between regular and plasmonic gratings in terms of fluorescent intensity. (Image courtesy of Shubhra Gangopadhyay/Nanoscale.)

August 2016

A multidisciplinary team of engineers, biologists and chemists is developing a new type of nanoscale microscope ­that will be cheaper and more accessible than existing electron microscopes.
A typical optical microscope is relatively simple, magnifying visible images using a series of lenses. However, due to limitations imposed by the wavelength of visible light, as well as the properties of the materials used, it is very difficult to achieve a resolution more precise than 200nm with an optical microscope.

To get around this problem, the team is using imaging based on surface plasmon resonance (SPR) to achieve resolutions down to 65 nanometers without the high cost of an electron microscope.

Surface Plasmon Resonance Explained
SPR occurs when visible light contacts a specialized surface consisting of a repeating metallic grating pattern atop a substrate. Resonance occurs between certain incident photons and the oscillating surface electrons, releasing a plasmon wave and absorbing the resonant frequency of light.

The resulting absorption pattern can then be measured by a detector.

Diagram of surface plasmon resonance (SPR). (Image courtesy of Wikipedia.)
The team used HD­DVD (remember those?) and Blu­Ray discs as templates for creating plasmonic gratings on microscopic slides. Because this technology is already prevalent, these gratings can be produced relatively inexpensively compared to other microscopy techniques of similar resolution.
Additionally, the team has used glancing angle deposition (GLAD) to create nano­protrusions and nano­gaps in combination with the gratings in order to create localized SPR and allow for simultaneous imaging of larger areas.
Benefits of Low-Cost Nanoscale Microscopy
Until recently, nanoscale microscopy has been an expensive­ endeavor, despite being incredibly useful. The ability to view samples on the scale of nanometers allows for the diagnosis of diseases, creation of new materials, analysis of existing materials and many other applications.

However, the equipment necessary for nanoscale microscopy can be prohibitively expensive, especially for developing countries and small laboratories.

The team has already used plasmonic gratings to detect cortisol and tuberculosis on the nanometer scale. The team was led by Dr. Shubra Gangopadhyay, an electrical and computer engineering professor at the University of Missouri. She predicts that the technology could be used “to further detect a wide variety of diseases, particularly in developing countries.”

The research has been published under the title “Plasmonic gratings with nano­protrusions made by glancing angle deposition (GLAD) for single­ molecule super­resolution imaging” in the journal Nanoscale.

For more advancements in microscope technology, find out how engineers use spider silk to create a microscope superlens.


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