The new technology allows for a more precise view of the smallest nanoparticles

Current cutting-edge techniques have clear limitations when it comes to visualizing the smallest nanoparticles, making it difficult for researchers to study viruses and other structures at the molecular level.

Scientists from the University of Houston and the University of Texas MD Anderson Cancer Center reported in Nature Communications a new optical imaging technology for nano-scale objects, which relies on non-scattered light to detect nanoparticles up to 25 nanometers in diameter. The technology, known as PANORAMA, uses a glass slide coated with gold nanodiscs, allowing scientists to monitor changes in light transmission and determine target characteristics.

PANORAMA takes its name from Plasmonic Nano-aperture Label-free Imaging (PlAsmonic NanO-apeRture iMAging lAbel-free), signifying the key features 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 for the article, said the smallest transparent object a standard microscope can view is between 100 nanometers and 200 nanometers. This is mainly because, in addition to being so small, they don’t reflect, absorb or “scatter” enough light, which could allow imaging systems to detect their presence.

Labeling is another commonly used technique; it requires researchers to know something about the particle they’re studying – that a virus has a spike protein, for example – and to design a way to label that feature with fluorescent dye or some other method to more easily detect the particle.

“Otherwise, it will appear invisible as a tiny particle of dust under a microscope, because it’s too small to detect,” Shih said.

Another drawback? Labeling is only useful if researchers already know at least something about the particle they want to study.

“With PANORAMA, you don’t have to do the labeling,” Shih said. “You can view it directly because PANORAMA is not based on detecting scattered light from the nanoparticle.”

Instead, the system allows observers to detect a transparent target as small as 25 nanometers by monitoring the transmission of light through the glass coated with gold nanodiscs. By monitoring changes in light, they are able to detect nearby nanoparticles. The optical imaging system is a standard bright field microscope commonly found in any laboratory. There are no lasers or interferometers required in many other unlabeled imaging technologies.

“The size limit was not reached, according to the data. We stopped at 25nm nanoparticles simply because this is the smallest polystyrene nanoparticle on the market,” Shih said.