Finding defects in two-dimensional materials

A new imaging approach developed by NCCR Bio-Materials researchers could help zoom in on the workings of cells. This innovative compact platform could constitute an important step toward getting unprecedented insights into nanoscale processes.

Microscopes have been around since the 16^th century, but their basic design barely changed as it has proven challenging to miniaturize. Now, NCCR Bio-inspired Materials researchers at Lausanne’s Federal Insitute of Technology (EPFL) have developed a super-compact, high-resolution imaging platform that may find important applications in biology. “In microscopes, you have a sample stage, you have objectives, you have lenses, you have detectors, and you typically have a laser or some illumination part, which is often very big,” says NCCR Principal Investigator Prof. Aleksandra Radenovic, who leads the Laboratory of Nanoscale Biology at EPFL. “Our goal was to make a platform that would shrink the microscope to a very, very small chip.”

Previous work by Radenovic’s team produced tiny optical waveguides, about 100 micrometers in size, which the researchers used to image 2D crystals — a class of materials characterized by a single layer of regular atomic structures. Such materials can be used in wide-ranging applications, including electronics and biosensors. However, transferring 2D crystals from the growth substrate to the imaging chip can introduce contamination, which may prevent researchers from accurately characterizing the crystals’ structure and properties. To make up this shortfall, Radenovic and her colleagues developed an approach to grow a widely used 2D crystal directly on the optical waveguides of a chip. Each chip contains tens of thousands of waveguides on which the researchers grew their material. Then, they shed a laser light into the waveguides to image and characterize defects in the intact 2D crystal.

Although the 2D crystal is typically non-fluorescent, small defects within it are fluorescent. Such defects are reminiscent of nanosized diamond particles that are used as miniaturized sensors of magnetic or electrical fields, temperature and ion concentration. “Measuring temperature, magnetic field or electrical field at nanoscales can be super interesting in biology,” Radenovic says. Because of the similarities between 2D crystals and nanodiamonds, the new imaging approach could be used to provide insights into key biological phenomena. “We know that genetically identical cells could produce completely different amounts of proteins because of small local changes,” Radenovic says. “This novel platform could help us to look — locally and non-invasively — at ion concentration and temperature changes as a cell engages in metabolic processes.” In such a scenario, researchers would grow cells directly on the chip and use the optical waveguides coupled with 2D crystals or nanodiamonds as a probe.

The chip is easily manufactured, can operate on many different microscopes and sustain harsh treatments, including the high temperatures that are used for growing 2D materials and nanodiamonds, Radenovic says. In the future, she adds, “one could even imagine to shrink it further.” The findings were published in the journal ACS Photonics. The development of this and other approaches to access the world of nanoscale materials was made possible thanks to the interdisciplinary nature of the NCCR Bio-inspired Materials, Radenovic says. “Together, we are pushing the frontiers of where and what one can measure.”

Reference:  Glushkov, E.; Mendelson, N.; Chernev, A.; Ritika, R.; Lihter, M.; Zamani, R. R.; Comtet, J.; Navikas, V.; Aharonovich, I.; Radenovic, A. Direct Growth of Hexagonal Boron Nitride on Photonic Chips for High-Throughput Characterization. ACS Photonics 2021, 8 (7), 2033–2040.https://doi.org/10.1021/acsphotonics.1c00165

Author: Giorgia Guglielmi