In new research published in Nature Synthesis, University of Illinois at Urbana-Champaign bioengineering professor Andrew Smith and postdoctoral researcher Wonseok Lee have developed HgSe and HgCdSe quantum dots that absorb and emit in the infrared. These were created using well-developed, visible spectrum CdSe precursors, and the new nanocrystal products retained the desired properties of the parent CdSe nanocrystals, including size, shape, and uniformity. This is the first example of infrared quantum dots that match the quality of those in the visible spectrum, according to Smith.
Smith had been attempting to create this material since his graduate school days, with no success. The broader research community had also seen no success in this area until now. Smith explained that their success came from using cadmium selenide, the most developed quantum dot in the visible spectrum, as a ‘sacrificial mould’. By replacing the cadmium atoms with mercury atoms, the quantum dots instantly shifted into the infrared spectrum, retaining all desired qualities: strong light absorption, strong light emission, and homogeneity.
In their paper ‘Interdiffusion-enhanced cation exchange for HgSe and HgCdSe nanocrystals with infrared bandgap’, published in Nature Synthesis, Smith and Lee described their novel approach. They abandoned the traditional method of synthesising nanocrystals, which involves mixing precursor elements and allowing them to decompose into the desired form under the right conditions. However, no one had found suitable conditions for mercury, cadmium, and selenide. Lee developed a new process called interdiffusion enhanced cation exchange, where a fourth element, silver, was added. This introduced defects in the material, causing everything to mix homogeneously, solving the problem.
Quantum dots have many applications, but one with the most potential impact is as molecular probes for imaging in biological systems. Since most quantum dots emit in the visible spectrum, only emissions near the skin’s surface can be detected. Biology, however, is fairly transparent in the infrared, allowing deeper tissues to be probed. Mice, the standard models for most diseases, could be studied more effectively. With infrared-emitting quantum dots, researchers could see almost entirely through a living rodent, observing its physiology and the locations of specific molecules throughout the body. This would enhance understanding of biological processes and aid in developing therapeutics without sacrificing the mice, potentially transforming preclinical drug development.
This research was funded by the US National Institutes of Health and the National Science Foundation.
This breakthrough signifies a major advancement in the field of quantum dots, paving the way for new applications and deeper insights into biological systems.
Nanoco Group PLC (LON:NANO) leads the world in the research, development and large-scale manufacture of heavy metal-free nanomaterials for use in displays, lighting, vertical farming, solar energy and bio-imaging.
