Nanobiosensor Technology Gives New Access To Living Cell's Molecular Processes

The "nanobiosensor" allows scientists to physically probe inside a living cell without destroying it. As scientists adopt a systems approach to studying biomolecular processes, the nanobiosensor provides a valuable tool for intracellular studies that have applications ranging from medicine to national security to energy production.

ORNL Corporate Fellow and Life Sciences Division researcher Tuan Vo-Dinh leads a team of researchers who are developing the nanoscale technology. "This research illustrates the integrated 'nano-bio-info' approach to investigating and understanding these complex cell systems," Vo-Dinh said. "There is a need to explore uncharted territory inside a live cell and analyze the molecular processes. This minimally invasive nanotechnology opens the door to explore the inner world of single cells".

ORNL's work was most recently published in the Journal of the American Chemical Society and has appeared in a feature article of the journal Nature. Members of Vo-Dinh's research team include postdoctoral researchers Paul M. Kasili, Joon Myong Song and research staff biochemist Guy Griffin.

The group's nanobiosensor is a tiny fiber-optic probe that has been drawn to a tip of only 40 nanometers (nm) across--a billionth of a meter and 1,000 times smaller than a human hair. The probe is small enough to be inserted into a cell.

Immobilized at the nanotip is a bioreceptor molecule, such as an antibody, DNA or enzyme that can bind to target molecules of interest inside the cell. Video microscopy experiments reveal the minimally invasive nature of the nanoprobe in that it can be inserted into a cell and withdrawn without destroying it.

Because the 40-nm diameter of the fiber-optic probe is much narrower than the 400-nm wavelength of light, only target molecules bound to the bioreceptors at the tip are exposed to and excited by the evanescent field of a laser signal.

"We detect only the molecules that we target, without all the other background 'noise' from the myriad other species inside the cell. Only nanoscale fiber-optics technology can provide this capability," said Vo-Dinh.

ORNL's technology gives molecular biologists an important systems biology approach of studying complex systems through the nano-bio-info route. Conventional analytical methods--electron microscopy or introducing dyes, for example--have the disadvantage of being lethal to the cell.

"The information obtained from conventional measurements is an average of thousands or millions of cells," said Vo-Dinh. "When you destroy cells to study them, you can't obtain the dynamic information from the whole live cell system. You get only pieces of information. Nanosensor technology provides a means to preserve a cell and study it over time within the entire cell system."

The ability to work with living cells opens a new path to obtaining basic information critical to understanding the cell's molecular processes. Researchers have a new tool for understanding how toxic agents are transported into cells and how biological pathogens trigger biological responses in the cell.

Vo-Dinh's team recently detected the biochemical components of a cell-signaling pathway, apoptosis. Apoptosis is a key process in an organism's ability to prevent disease such as cancer. This programmed cell-death mechanism causes cells to self-destruct before they can multiply and introduce disease to the organism.

"When a cell in our body receives insults such as toxins or inflammation and is damaged, it kills itself. This is nature's way to limit and stop propagation of many diseases such as cancer," said Vo-Dinh. "For the first time we've seen apoptosis occur within a single living cell."

Apoptosis triggers a host of tell-tale enzyme called caspases. Vo-Dinh's team introduced a light-activated anti-cancer drug into cancer cells. They then inserted the fiberoptic nanoprobe with a biomarker specific for caspase-9 attached to its tip. The presence of caspase-9 caused cleavage of the biomarker from the tip of the nanobiosensor. Changes in the intensity of the biomarker's fluorescence revealed that the light-activated anti-cancer drug had triggered the cell-death machinery.

"The nanobiosensor has many other applications for looking at how cells react when they are treated with a drug or invaded by a biological pathogen. This has important implications ranging from drug therapy development to national security, environmental protection and a better understanding of molecular biology at a systems level," said Vo-Dinh. "This area of research is truly at the nexus of nanotechnology, biology and information technology."

The research was supported by ORNL's laboratory-directed research and development program and by the DOE Office of Biological and Environmental Research in the Office of Science. ORNL is managed by UT-Battelle for the Department of Energy.