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Nanoscale device tracks subtle changes in brain chemistry

Professional Engineering

The fabricated and packaged nanodialysis device (Credit: The Grainger College of Engineering at University of Illinois Urbana-Champaign)
The fabricated and packaged nanodialysis device (Credit: The Grainger College of Engineering at University of Illinois Urbana-Champaign)

A new nanoscale sensor can monitor areas of the brain 1,000-times smaller than previous technology and can track subtle changes in chemical content with sub-second resolution, “greatly outperforming standard technologies”, according to its creators.

Developed by researchers at the University of Illinois Urbana-Champaign in Illinois, the silicon-based device takes advantage of techniques developed for microelectronics manufacturing.

“Longstanding challenges in biomedical research, such as monitoring brain chemistry and tracking the spread of drugs through the body, require much smaller and more precise sensors,” the research announcement said.

The new device’s small size reportedly enables it to monitor chemical content with close to 100% efficiency in highly localised regions of tissue.

“With our nanodialysis device, we take an established technique and push it into a new extreme, making biomedical research problems that were impossible before quite feasible now,” said Yurii Vlasov, co-lead of the study.

“Since our devices are made on silicon using microelectronics fabrication techniques, they can be manufactured and deployed on large scales.”

In microdialysis, a probe with a thin membrane is inserted into biological tissue. Chemicals pass through the membrane into a fluid that is pumped away for analysis. The ability to directly sample from tissue has made a major impact in fields such as neuroscience, pharmacology and dermatology.

“Traditional microdialysis has limitations,” the announcement said. The probes sample from a few square millimetres, so can only measure the average composition over relatively large regions in the tissue. The large size also results in some degree of tissue damage when the probe is inserted.

“Many problems with traditional microdialysis can be solved by using a much smaller device,” Vlasov said. “Going smaller with nanodialysis means more precision, less damage from the tissue placement, chemically mapping the tissue with higher spatial resolution and a much faster read-out time, allowing a more detailed picture of the changes in tissue chemistry.”

The most important feature of nanodialysis is the ultra-slow flow rate of the fluid pumped through the probe. By making the flow rate 1,000-times slower than traditional microdialysis, the device can capture the chemical composition of the tissue from an area 1,000-times smaller than traditional techniques.

“By drastically decreasing the flow rate, it allows the chemicals diffusing into the probe to match the concentrations outside in the tissue,” Vlasov said. “Imagine you’re adding dye to a pipe with flowing water. If the flow is too fast, the dye gets diluted to concentrations that are difficult to detect. To avoid dilution, you need to turn the water almost all the way down.”

Standard microdialysis devices are constructed using glass probes and polymer membranes, making them a challenge to miniaturise. To build devices suitable for nanodialysis, the researchers used techniques developed for electronic chip manufacturing to create a device based on silicon.

“In addition to enabling us to go smaller, silicon technology makes the devices cheaper,” Vlasov said. “By putting in the time and effort to develop a fabrication process for building our nanodevices on silicon, it is now very straightforward to manufacture them at industrial scales at an incredibly low cost.”

The work was published in ACS Nano.

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