CLEMSON, South Carolina — Visualizing biological cells under a microscope was just made clearer thanks to research conducted by graduate student Yifei Jiang and principal investigator Jason McNeill of Clemson University’s department of chemistry.

Principal investigator Jason McNeill (left) and his graduate student Yifei Jiang work together in the College of Science’s department of chemistry.

Principal investigator Jason McNeill (left) and graduate student Yifei Jiang work together in the College of Science’s department of chemistry.
Image Credit: Muskendol Novoa

With the help of Rhonda Powell and Terri Bruce of Clemson’s Light Imaging Facility, the team was able to develop a nanoparticle “switch” that fluoresces to sharpen the resolution of microscopic images that depict small cellular structures. As recently published in Nano Letters, this switch improves upon an imaging method that won the 2014 Nobel Prize in Chemistry.

As light passes around structures within biological cells, it diffracts, or bends, to a point that light microscopes cannot clearly resolve. The 2014 prize-winning imaging method — single molecule localization microscopy — was invented to surpass this limitation.

“Single molecule localization microscopy is based on molecular ‘photoswitches’ — fluorescent molecules that you can turn on and off like a light switch to beat the diffraction limit,” McNeill said. “With this imaging method, the sample is imaged one fluorescent molecule at a time and a computer is used to construct an image that is much sharper than what you could get with a regular light microscope.”

The constructed image appears as one illuminated picture, when in actuality it is a combination of several pictures of each individual photoswitch, or “blink.”

The catch, however, is that the fluorescence provided by photoswitches is too dim to fully discern cellular structures with only a slight improvement in image resolution. Single molecule localization microscopy also requires specialized equipment that can be expensive to obtain.

Cue the “buckyswitch,” the Clemson researchers’ enhanced version of a photoswitch. This new type of nanoparticle retains the photoswitch’s on-off capability, but is 10 times brighter and easier to use. It also allows microscopes to capture images up to the terapixel level. (That’s the equivalent of one trillion pixels or one million megapixels.)

“These nanoparticles are the first photoswitches to achieve precision down to approximately 1 nanometer, which greatly improves the resolution of super-resolution imaging,” Jiang said. “Also, our method only requires one light source, where conventional super-resolution techniques require two; thus, we have simplified the microscope setup.”

A series of fluorescence microscopy images detail the blinking behavior of the team's nanoparticle 'buckyswitches.'

A series of fluorescence microscopy images detail the blinking behavior of the team’s nanoparticle ‘buckyswitches.’
Image Credit: Nano Letters 17 (6) pp. 3896–3901

Jiang assembled the buckyswitch out of a fluorescent, semiconducting polymer complexed with a chemical derivative of buckminsterfullerene, which is a soccer-ball-shaped form of carbon. He then attached the nanoparticle buckyswitches to the surface of E. coli. As hoped, the buckyswitches emitted small flashes of light, which allowed the researchers to determine their precise positions. They then pieced together each flash of light to reconstruct the shape of the E. coli, yielding a super-resolution image.

“We hope this breakthrough will eventually be able to help researchers tackle difficult problems in biology leading to breakthroughs in the understanding and treatment of disease,” the Clemson team wrote.

The team designed the buckyswitches to work with standard fluorescent microscopes and free software that’s available online, making the technology inexpensive and accessible for labs worldwide.

Their publication, titled “Improved Superresolution Imaging Using Telegraph Noise in Organic Semiconductor Nanoparticles,” is featured in the June 14 issue of Nano Letters. The research detailed within this publication is supported by the National Science Foundation under grant number CHE-1412694.

For more on the Clemson team’s invention, please visit this link for an in-depth version of this story.

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