Current state-of-the-art techniques have clear limitations when it comes to imaging the smallest nanoparticles, making it difficult for researchers to study viruses and other structures at the molecular level.
In a paper in Nature Communications, scientists from the University of Houston (UH) and the University of Texas M.D. Anderson Cancer Center report a new optical imaging technology for nanoscale objects that relies on unscattered light to detect nanoparticles as small as 25nm in diameter. The technology, known as PANORAMA, uses a glass slide covered with gold nanodiscs to monitor changes in the transmission of light, allowing scientists to determine the characteristics of the nanoparticles.
PANORAMA takes its name from Plasmonic Nano-aperture Label-free Imaging (PlAsmonic NanO-apeRture lAbel-free iMAging), signifying the key characteristics of the technology. PANORAMA can be used to detect, count and determine the size of individual dielectric nanoparticles.
Wei-Chuan Shih, professor of electrical and computer engineering at UH and corresponding author of the paper, said the smallest object a standard microscope can image is between 100nm and 200nm in diameter. That’s mainly because – in addition to being so small – these objects don’t reflect, absorb or ‘scatter’ enough light to allow imaging systems to detect their presence.
Labeling is another commonly used technique for visualizing tiny objects. But it requires researchers to know something about the particle they are studying – that a virus has a spike protein, for example – and engineer a way to tag that feature with a fluorescent dye or some other method in order to more easily detect the particle.
“With PANORAMA, you don’t have to do the labeling,” Shih said. “You can view it directly because PANORAMA does not rely on detecting the scattered light from the nanoparticle.”
Instead, the system allows observers to detect a transparent target as small as 25nm by monitoring light transmission through the gold nanodisc-covered glass slide. By monitoring changes in the light transmission, they are able to detect the nearby nanoparticles. The optical imaging system is a standard bright-field microscope commonly found in any lab. There is no need for the lasers or interferometers that are required in many other label-free imaging technologies.
“The size limit has not been reached, according to the data. We stopped at 25nm nanoparticles simply because that is the smallest polystyrene nanoparticle on the market,” Shih said.
This story is adapted from material from the University of Houston, with editorial changes made by Materials Today. The views expressed in this article do not necessarily represent those of Elsevier. Link to original source.