A new, noninvasive method to control neurons uses the unique optical and electrical properties of quantum dots (QDs).
Optically excited quantum dots in close proximity to a cell control the opening of ion channels.
A new, noninvasive method to control neurons uses the unique optical and electrical properties of quantum dots (QDs). Researchers at the University of Washington (U.S.A.) showed that neurons and other cells changed their behavior in specific ways when nearby QDs were optically excited (Biomed. Opt. Express 3, 447). The new method provides a tool that could target particular cell types, which would help researchers investigating brain function, including research into Parkinson’s disease, Alzheimer’s and depression.
Electrical impulses can activate neurons, but using electrodes for delivering the impulses turns on thousands or millions of them all at once. This makes it impossible to tease out the behavior of an individual or specific type of cell. Optical methods of triggering neurons are attractive because light is noninvasive and reduces other changes in the environment. The University of Washington team led by Fred Rieke and Lih Y. Lin used QDs to make cells photosensitive without genetically or chemically changing them.
QD electrons have limited energy bands because they are so small—only a few microns in diameter, which is roughly the thickness of a cell membrane. This results in precisely defined absorption and emission wavelengths, as well as magnetic fields created by electrons moving between the few allowed energy levels. Also, QDs can be attached to proteins designed to seek out receptors on the surface of specific cell types. These characteristics can turn QDs into a kind of beacon, making it possible for researchers to identify and precisely activate cells.
The proof-of-concept experiments were done on glass, not in the body. The researchers grew cells on QD films so that their membranes were close to the QD-coated surfaces. When light excites electrons in the QDs, they generate a magnetic field, which then triggers measurable changes in the ion-channel activity on the cell surface.
They used cadmium-telluride and cadmium-selenium QDs to investigate prostate cancer cells first (because of their resilience) and then brain neurons. The researchers observed that the ion channels in the cancer and brain cell membranes were activated when the QDs were excited.
Researchers need to identify a non-toxic material for QDs before they can be used in vivo. But the technique developed by Reike and Lin’s team offers the potential to manipulate the activity of specific types of neurons, which could elucidate—or even be used to treat—brain diseases. “Many brain disorders are caused by imbalanced neural activity,” Rieke says. “This could aid both in understanding the normal activity patterns in neural circuits, by introducing perturbations and monitoring their effect, and how such manipulations could restore normal circuit activity.”
Yvonne Carts-Powell is a freelance science writer who specializes in optics and photonics.