illustration of the quantum measurement carried out on a single atom quantum sensor in a living human HeLa cell. The atom sensor is encased in a nanodiamond particle and is controlled by external microwaves and laser light, and tracked by its emission of red light. The information gleaned is of a quantum nature, where the states of the atom exist in two quantum states at the same time prior to measurement.
Credit: David Haworth
DUBLIN: An atomic-sized impurity sitting in a diamond crystal has allowed scientists to explore the nano-scale environment inside a living human cell.
The new sensor can detect biological processes at the molecular level, such as the regulation of chemicals in and out of a cell, which is critical to understanding how drugs work.
"This research paves the way towards a new class of quantum sensors used for biological research into the development of new drugs and nanomedicine," said Lloyd Hollenberg of the University of Melbourne, who led the study in the current issue of Nature Nanotechnology.
Centres of impurity
The use of a NV (nitrogen vacancy) centre as an atomic-sized magnetic probe was first suggested in 2008. This impurity is comprised of a single nitrogen atom (N) sitting next to a missing carbon (vacancy, V) in the diamond lattice.
Until now, the measurement of NV nanodiamonds in biology had been limited to collecting its fluorescence as a position marker.
The study by Hollenberg and his colleagues showed that the quantum measurement of the NV system can be carried out in the biological environment, that the information obtained significantly improves its use as a fluorescent beacon and that these measurements do not degrade the cell.
"We incorporated nanodiamonds (about 50 nanometres in size) containing NV centres into living HeLa cells, a human cancer cell line," Hollenberg explained. "The quantum state of the NV system in a nanodiamond was controlled and monitored while it moved within the cell."
A valuable compass
Due to its quantum properties, the NV system acted like a nanoscale compass from which the scientists could infer its orientation at a given time and the degree to which it was affected by tiny local magnetic fluctuations, themselves the result of biological processes.
In nanomedicine, drugs are delivered to the target via specifically tailored nanoparticles, so it is important to understand how nanoparticles are taken up and move within the cells.
"The NV nanodiamond quantum probe could provide new information over long-time scales of how such particles move and where they end up for a given surface functionalisation," said Hollenberg.
In drug discovery, researchers need to measure the action of drugs on ion channels, which control the flow of ions through the cell membrane. The NV system is sensitive to ions flowing through such channels and so could act as a non-invasive sensor, Hollenberg said.
Probes in living objects
This work marks a breakthrough in this area, according to Viatcheslav Dobrovitski, scientist at the Ames Laboratory of the U.S. Department of Energy in Iowa. "It shows that NV centres in nano-sized diamond crystals can actually work as local probes in living biological objects, monitoring their life and death," he said.
"This work clearly demonstrates that the changes in the magnetic environments generated by living organisms can be accurately measured and linked to the biological process," Dobrovitski added.
He said, in future, one could imagine using the targeted placement of the NV centres in different parts of the cell to track specific biological functions.
Quantum physicist and PhD student Liam McGuinness from the University of Melbourne who was involved in the study said that monitoring the atomic sensor in living cells was a considerable achievement. "Previously, these atomic level quantum measurements could only be achieved under carefully controlled conditions of a physics lab," he said.
