WIRE)–By harnessing quantum dots-tiny light-emitting semiconductor
particles a few billionths of a meter across-researchers at the University of Washington
(UW) have developed a new and vastly more targeted way to stimulate neurons in
the brain. Being able to switch neurons on and off and monitor how they
communicate with one another is crucial for understanding-and, ultimately,
treating-a host of brain disorders, including Parkinsons disease, Alzheimers,
and even psychiatric disorders such as severe depression. The research was
published today in the Optical Societys (OSA) open-access journal Biomedical Optics Express.
Doctors and researchers today commonly use electrodes-on the
scalp or implanted within the brain-to deliver zaps of electricity to stimulate
cells. Unfortunately, these electrodes activate huge swaths of neural
territory, made up of thousands or even millions of cells, of many different
types. That makes it impossible to tease out the behavior of any given cell, or
even of particular cell types, to understand cellular communication and how it
contributes to the disease process.
Ideally, nerve cells would be activated in a non-invasive
way that is also highly targeted. A promising method for doing this is
photostimulation-essentially, controlling cells with light. Recently, for
example, a team of Stanford University researchers altered mammalian nerve
cells to carry light-sensitive proteins from single-celled algae, allowing the
scientists to rapidly flip the cells on and off, just with flashes of light.
The problem with this process, however, is that the light-controlled cells must
be genetically altered to perform their parlor trick.
An alternative, says the UW team, led by electrical engineer
Lih Y. Lin and biophysicist Fred Rieke, is to use quantum dots-tiny
semiconductor particles, just a few billionths of a meter across, that confine
electrons within three spatial dimensions. When these otherwise trapped
electrons are excited by electricity, they emit light, but at very precise
wavelengths, determined both by the size of the quantum dot and the material
from which it is made. Because of this specificity, quantum dots are being
explored for a variety of applications, including in lasers, optical displays,
solar cells, light-emitting diodes, and even medical imaging devices.
In the paper published today, Lin, Rieke and colleagues have
extended the use of quantum dots to the targeted activation of cells. In
laboratory experiments, the researchers cultured cells on quantum dot films, so
that the cell membranes were in close proximity to the quantum-dot coated
surfaces. The electrical behavior of individual cells was then measured as the
cells were exposed to flashes of light of various wavelengths; the light
excited electrons within the quantum dots, generating electrical fields that
triggered spiking in the cells.
“We tried prostate cancer cells first because a colleague
happened to have the cell line and experience with them, and they are
resilient, which is an advantage for culturing on the quantum dot films,” Lin
says. “But eventually we want to use this technology to study the behavior of
neurons, so we switched to cortical neurons after the initial success with the
The experiments, says Lin, show that “it is possible to
excite neurons and other cells and control their activities remotely using
light. This non-invasive method can provide flexibility in probing and
controlling cells at different locations while minimizing undesirable effects.”
“Many brain disorders are caused by imbalanced neural
activity,” Rieke adds, and so “techniques that allow manipulation of the
activity of specific types of neurons could permit restoration of
normal-balanced-activity levels”-including the restoration of function in
retinas that have been compromised by various diseases. “The technique we
describe provides an alternative tool for exciting neurons in a spatially and
temporally controllable manner. 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
So far, the technique has only been applied to cells
cultured outside the body; to gain insight into disease processes and be
clinically useful, it would need to be performed within living tissue. To do
so, Lin says, “we need to modify the surface of the quantum dots so that they
can target specific cells when injected into live animals.” The dots also need
to be non-toxic, unlike those used in the Biomedical Optics Express report,
which often had detrimental effects on the cells to which they were attached.
“One solution would be developing non-toxic quantum dots using silicon,” Lin
In addition to Lin and Rieke, the other coauthors on the
paper are UW graduate student Katherine Lugo and former graduate student Xiaoyu
Paper: “Remote switching of cellular activity and cell signaling using
light in conjunction with quantum dots,” Biomedical Optics Express, Vol. 3,
Issue 3, pp. 447-454 (2012).
About Biomedical Optics Express
Biomedical Optics Express is OSAs principal outlet for serving the biomedical
optics community with rapid, open-access, peer-reviewed papers related to
optics, photonics and imaging in the life sciences. The journal scope
encompasses theoretical modeling and simulations, technology development, and
biomedical studies and clinical applications. It is published by the Optical
Society and edited by Joseph A. Izatt of Duke University.
Biomedical Optics Express is an open-access journal and is available at no cost
to readers online at http://www.OpticsInfoBase.org/BOE.
Uniting more than 130,000 professionals from 175 countries, the Optical Society
(OSA) brings together the global optics community through its programs and
initiatives. Since 1916 OSA has worked to advance the common interests of the
field, providing educational resources to the scientists, engineers and
business leaders who work in the field by promoting the science of light and
the advanced technologies made possible by optics and photonics. OSA
publications, events, technical groups and programs foster optics knowledge and
scientific collaboration among all those with an interest in optics and
photonics. For more information, visit www.osa.org.