Nanotech News

July 5, 2005

Fiber-Optic Nanosensor Monitors Single Cells

Combining nanoscale technologies with fiber optics, researchers are developing a host of new tools for monitoring the intricate biochemical and genetic events that occur within a single cell. A paper by Tuan Vo-Dinh, Ph.D., at Oak Ridge National Laboratory, reviews the emerging field of single-cell monitoring with fiber-optic nanosensors and presents experimental results from the author's laboratory.

Writing in the journal Analytical and Bioanalytical Chemistry, Dinh and graduate student Paul Kasili, define a fiber optic nanoscale as a nanometer-scale measurement device that consists of a biologically or chemically sensitive layer, such as an immobilized receptor, antibody, or nucleic acid, that is covalently attached to an optical transducer. In the case of a receptor-based nanosensor, an interaction between the immobilized receptor and its substrate - the molecule it binds to - produces a perturbation that the optical transducer converts to an electrical signal via laser-induced fluorescence.

Preparing fiber optic nanosensors is fairly straightforward, according to the authors. Using the so-called "heat and pull" method, a large diameter silica optical fiber is placed in a commercially available puller that heats the fiber using a carbon dioxide laser and then pulls the fiber to the desired thickness, usually around 50 nanometers in diameter. The pulled fiber is then cut in half, yielding two nanoscale fiber tips. Vapor deposition is then used to deposit a thin layer of silver, aluminum or gold on the side walls of the tip, followed by a two-step chemical treatment of the tip that provides covalent attachment points for the biosensor molecules.

The authors present several examples of how to use these sensors in applications ranging from measurement of environmental carcinogens to quantification of cytochrome c activity as a measure of cellular energy metabolism. Several types of biological nanosensors for monitoring apoptosis are discussed in detail, including one device that measures activation of capsase-9, one of the earliest events in apoptosis.

This work and other examples are detailed in a paper titled, "Fiber-optic nanosensors for single-cell monitoring." This work was posted online in advance of publication. An abstract is available at the journal's website.
View abstract.