Last updated February 22, 2018 at 10:00 am
Physicists have overcome a fundamental physical problem with ultra-small nanoparticles to develop the smallest temperature sensor ever.
A new type of nanoparticle, called “thermal dots”, overcomes the restraints of ‘thermal quenchings’. Credit: University of Technology Sydney
The researchers have dubbed their new creation a “thermal dot” that has the potential to revolutionise display technologies, security inks, and bio-imaging.
The thermal dots are a so-called “upconverting nanoparticles” that are able to absorb low-energy photons from infrared light – or heat – and emit higher-energy photons, such as visible light.
But the tricky problem with this, which has always faced scientists, is how to make nanoparticles even smaller while also retaining these useful properties.
In upconverting nanoparticles surface vibrations are key to their light emission properties, and so the smaller the particle is, the dimmer and less useful it becomes.
This “thermal quenching” affects the performance of opto-electronics materials, displays and fluorescence probes.
But with the thermal dots, researchers at the Institute of Biomaterials and Medical Devices (IBMD) at the University of Technology in Sydney have found a way to control the surface chemistry to enhance light emission.
These new engineered particles display a 1,000-fold increase in brightness.
“The problem was once you push the size of nanoparticles smaller than 10 nanometres [8,000 times smaller than the width of a single human hair], the brightness and efficiency dropped dramatically,” explains Dayong Jin, director of IBMD and co-author of the study and winner of the 2017 Malcolm McIntosh Prize for Physical Scientist of the Year.
This dimming is due to a dark surface layer that is optically inactive. But the team discovered that this dark layer is sensitive to temperature.
By using thermal energy to light up the layer, they showed that very small nanoparticles can still fluoresce efficiently.
This process relies on ions of the metallic element ytterbium on the surface of the nanoparticles, which assist the energy transfer that generates light emission.
Lead author Jiajia Zhou says this discovery will have a broad range of applications. She highlights “the potential for new types of nanosensors for early disease diagnosis, including highly sensitive nanothermometers that can provide a non-invasive way to answer many biological questions at the nanoscale such as how cells develop and differentiate in cancer”.
Thermal Dots can also be used in bio-imaging, display technologies, and security inks for fraud and anti-counterfeiting detection.
Enrico Della Gaspera, a nanotechnology researcher at RMIT University who was not involved in the study, hopes that these exciting results can soon be applied to other emitting nanomaterials.
He comments, however, that “too much heat will still rapidly degrade the light emission properties, therefore these materials won’t find use in applications where high temperatures, above about 250°C, are required”.
The research was published in Nature Photonics.
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