The novel camera comprises tiny semiconductor nanocrystals called quantum dots and gold nanoparticles, held together with molecular glue called cucurbituril (CB). When added to water with the molecule to be studied, the components self-assemble in seconds into a stable, powerful tool that allows the real-time monitoring of chemical reactions. Image: University of Cambridge.Researchers have made a tiny camera, held together with ‘molecular glue’, that allows them to observe chemical reactions in real time.
The camera, made by a team from the University of Cambridge in the UK, combines tiny semiconductor nanocrystals called quantum dots and gold nanoparticles, held together by a molecular glue called cucurbituril (CB). When added to water with the molecule to be studied, the components self-assemble in seconds into a stable, powerful tool that allows the real-time monitoring of chemical reactions.
This tool works by harvesting light within the semiconductors, inducing electron transfer processes like those that occur in photosynthesis, which can be monitored using the incorporated gold nanoparticle sensors and spectroscopic techniques. The researchers were able to use the camera to observe chemical species that had been previously theorized but not directly observed.
The tiny camera could be used to study a wide range of molecules for a variety of potential applications, such as improving photocatalysis and photovoltaics for renewable energy. The researchers report their work in a paper in Nature Nanotechnology.
Nature controls the assembly of complex structures at the molecular scale through self-limiting processes. However, mimicking these processes in the lab is usually time-consuming, expensive and reliant on complex procedures.
“In order to develop new materials with superior properties, we often combine different chemical species together to come up with a hybrid material that has the properties we want,” said Oren Scherman, a professor in Cambridge’s Department of Chemistry, who led the research. “But making these hybrid nanostructures is difficult, and you often end up with uncontrolled growth or materials that are unstable.”
The new method that Scherman and his colleagues from Cambridge’s Cavendish Laboratory and University College London in the UK came up with uses cucurbituril – a molecular glue that interacts strongly with both semiconductor quantum dots and gold nanoparticles. The researchers used the small semiconductor nanocrystals to control the assembly of the larger gold nanoparticles through a process they called interfacial self-limiting aggregation. This process leads to permeable and stable hybrid materials that interact with light, allowing the resulting camera to be used to observe photocatalysis and track light-induced electron transfer.
“We were surprised how powerful this new tool is, considering how straightforward it is to assemble,” said first author Kamil Sokolowski, also from Cambridge's Department of Chemistry.
To make their nano camera, the team added the individual components, along with the molecule they wanted to observe, to water at room temperature. Previously, when gold nanoparticles were mixed with the molecular glue in the absence of quantum dots, the components underwent unlimited aggregation and fell out of solution. However, with the strategy developed by the researchers, the quantum dots mediate the assembly of these nanostructures so that the semiconductor-metal hybrids control and limit their own size and shape. In addition, these structures can stay stable for weeks.
“This self-limiting property was surprising, it wasn’t anything we expected to see,” said co-author Jade McCune, also from Cambridge's Department of Chemistry. “We found that the aggregation of one nanoparticulate component could be controlled through the addition of another nanoparticle component.”
When the researchers mixed the components together, they were able to use spectroscopy to observe chemical reactions in real time. With the camera, they could observe the formation of radical species – a molecule with an unpaired electron – and products of their assembly such as sigma dimeric viologen species, where two radicals form a reversible carbon-carbon bond. The latter species had been theorized but never observed.
“People have spent their whole careers getting pieces of matter to come together in a controlled way,” said Scherman, who is also director of the Melville Laboratory. “This platform will unlock a wide range of processes, including many materials and chemistries that are important for sustainable technologies. The full potential of semiconductor and plasmonic nanocrystals can now be explored, providing an opportunity to simultaneously induce and observe photochemical reactions.”
“This platform is a really big toolbox considering the number of metal and semiconductor building blocks that can be now coupled together using this chemistry– it opens up lots of new possibilities for imaging chemical reactions and sensing through taking snapshots of monitored chemical systems,” said Sokolowski. “The simplicity of the setup means that researchers no longer need complex, expensive methods to get the same results.”
Researchers in the Scherman lab are currently working to further develop these hybrids for the real-time monitoring of electron-transfer processes in artificial photosynthetic systems and (photo)catalysis. The team is also looking at mechanisms of carbon-carbon bond formation as well as electrode interfaces for battery applications.
This story is adapted from material from the University of Cambridge, with editorial changes made by Materials Today. The views expressed in this article do not necessarily represent those of Elsevier. Link to original source.