| Mar 19, 2025 |
Researchers reveal how microbes receive electrons from quantum dots, enabling nano-biohybrids to harvest sunlight for advanced chemical transformations.
(Nanowerk News) Peanut butter and jelly. Simon and Garfunkel. Semiconductors and bacteria.
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Some combinations are more durable than others. In recent years, an interdisciplinary team of Cornell researchers has been pairing microbes with quantum dots, with the goal of creating nano-biohybrid systems that can harvest sunlight to perform complex chemical transformations for materials and energy applications.
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Now, the team has for the first time identified exactly what happens when a microbe receives an electron from a quantum dot: The charge can either follow a direct pathway or be transferred indirectly via the microbe’s shuttle molecules.
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The findings were published in Proceedings of the National Academy of Sciences (“Spatially resolved charge-transfer kinetics at the quantum dot–microbe interface using fluorescence lifetime imaging microscopy”). The lead author is Mokshin Suri ’24.
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“To put it succinctly, we discovered that there are different pathways for communicating,” said senior author Tobias Hanrath, the David Croll Professor of Engineering in the Smith School of Chemical and Biomolecular Engineering in Cornell Engineering. “That, in and of itself, has been suspected and discussed, but it hasn’t been precisely quantified and imaged like we’ve done. This is the very first fundamental step towards a long-term vision of combining digital information processing with microbial biochemistry.”
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The project was launched in 2019 with support from the U.S. Department of Energy’s Office of Biological and Environmental Research. The effort brought together the microscopy capabilities of Peng Chen, the Peter J.W. Debye Professor of Chemistry in the College of Arts and Sciences, with the synthetic biology expertise of Buz Barstow, Ph.D. ’09, assistant professor of biological and environmental engineering in the College of Agriculture and Life Sciences, and Hanrath, the self-described “particle guy.” In 2023, the team developed a platform to image their biohybrid systems with single-cell resolution and essentially parse out where the electrochemical activity occurred.
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For the new study, the researchers decided to use a different but complimentary approach, specifically to understand how to knock an electron out of a quantum dot and into a microbe. They turned to Warren Zipfel, associate professor of biomedical engineering in Cornell Engineering, who specializes in using optical microscopy for biomedical research, such as analyzing tissue.
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“The nice a-ha moment that Mokshin contributed to this was the recognition that you can use that same tool to probe interactions between the quantum dot and the microbe that had never been done before,” Hanrath said. “So there’s a novelty, just in a measurement by itself, beyond the insights that came out of it.”
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Quantum dots are characterized by strong light-matter interactions, and their optical and electronic properties can be custom-tailored by changing their size – capabilities that were recognized with the 2023 Nobel Prize in Chemistry. They have already found their way into commercial technologies in the form of QD LED displays, whereby an electron is injected and a photon pops out. They work the other way, too.
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“In our study, we essentially leveraged the LED functionality in reverse,” Hanrath said. “Instead of emitting a photon from an injected electron, we inject a photon and watch how the electrons are injected from the illuminated quantum dot to the nearby microbe.”
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While quantum dots have strong interactions with light, they are limited to relatively basic chemical transformations, and the opposite is true for microbial cells, Hanrath said. That’s why a quantum dot-microbe hybrid has such strong potential synergy.
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Using fluorescence lifetime imaging microscopy with two-photon excitation on a cadmium selenide quantum dot and Shewanella oneidensis bacteria, the researchers identified a distinct halo surrounding the microbe, which suggested the charge transfer was receiving some peripheral assistance. It turns out that an electron can either move directly from the quantum dot to the microbe or it can be transferred from the microbe via shuttle molecules, called redox mediators.
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“They have different rates, different sort of characteristic time constants,” Hanrath said. “And you can measure that with the fluorescence lifetime measurements that we’ve done.”
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Photosynthetic biohybrids of this sort could potentially convert carbon dioxide into value-added chemical products, such as bioplastics and biofuels, and control other microbe processes.
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“It’s exciting to think about all of the things that could be possible if you merge digital information processing with what the microbe does,” Hanrath said. “If you have some way of communicating with the microbe, you can direct it to do things that it otherwise wouldn’t have done or that would be really difficult to do by other means.”
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