Researchers have identified the “world’s most sensitive nanoparticle” and can measure it from a distance, using light.

The discovery, by a team of researchers from Macquarie University, the University of Adelaide, and Peking University, opens the way for rapid localization and measurement of cells within a living environment at the nanoscale.

These super-bright, photostable nanocrystals enable a new approach to highly advanced sensing technologies using optical fibers to interact with tiny (nanoscale) volumes of liquid.

For example, they can sense changes to a single living cell in the human body in response to chemical signals, the researchers say.

“Up until now, measuring a single nanoparticle would have required placing it inside a very bulky and expensive microscope,” says Professor Tanya Monro, Director of the University of Adelaide’s Institute for Photonics and Advanced Sensing (IPAS) and ARC Australian Laureate Fellow. “For the first time, we’ve been able to detect a single nanoparticle at one end of an optical fiber from the other end. That opens up all sorts of possibilities in sensing.”

This represents a sensitivity improvement of three orders of magnitude over benchmark nanocrystals such as quantum dots, the researchers say in a Nature Nanotechnology paper.

Sensing inside a living brain or a cell’s reaction to a cancer drug

“Using optical fibers we can get to many places such as inside the living human brain, next to a developing embryo, or within an artery — locations that are inaccessible to conventional measurement tools.

“This advance ultimately paves the way to breakthroughs in medical treatment. For example, measuring a cell’s reaction in real time to a cancer drug means doctors could tell at the time treatment is being delivered whether or not a person is responding to the therapy.”

The performance of sensing at the molecular level was previously limited by both insufficient signal strength and interference from background noise.

The special optical fiber engineered at IPAS also proved useful in understanding the properties of nanoparticles. “Material scientists have faced a huge challenge in increasing the brightness of nanocrystals,” says Dr. Jin, ARC Fellow at Macquarie University’s Advanced Cytometry Laboratories.

“Using these optical fibers, however, we have been given unprecedented insight into the light emissions. Now, thousands of emitters can be incorporated into a single SuperDot, creating a far brighter, and more easily detectable nanocrystal.”

Under infrared illumination, these SuperDots selectively produce bright blue, red, and infrared light, with 1,000 times more sensitivity than existing materials. “Neither the glass of the optical fiber nor other background biological molecules respond to infrared, so that removed the background signal issue. By exciting these SuperDots we were able to lower the detection limit to the ultimate level: a single nanoparticle,” says Jin.

“These joint efforts will ultimately benefit patients around the world. For example, our industry partners Minomic International Ltd and Patrys Ltd are developing uses for SuperDots in cancer diagnostic kits, detecting incredibly low numbers of biomarkers within conditions like prostate and multiple myeloma cancer.”

Macquarie is now actively seeking other industrial partners with the capacity to jointly develop solutions outside of these fields.