Aptamer nanoflares for molecular detection in living cells

By combining a gold nanoparticle with a unique family of nucleic acids, researchers at Northwestern University have created a new type of intracellular reporting system that with a flash of light reveals the presence and quantity of a wide variety of biologically important molecules. These so-called nanoflares could provide cancer biologists with a highly sensitive method of tracking complex biochemical processes in real time without interfering with those processes.

Chad A. Mirkin, Ph.D., principal investigator of the Nanomaterials for Cancer Diagnostics and Therapeutics at the Northwestern University Center of Cancer Nanotechnology Excellence, and his colleagues demonstrated the utility of their nanoflares by developing a real-time assay for intracellular adenosine triphosphate (ATP), one of the key energy sources of cellular metabolism. Current methods for ATP analysis require that a cell be destroyed and provide only an average measurement of ATP levels from large number of cells rather than time- and cell-specific measurements. The researchers reported their findings in the journal Nano Letters.

At the center of the nanoflare is a gold nanoparticle coated with a dense layer of nucleic acid aptamers. Aptamers, which are synthesized in the lab, are molecules designed to mimic antibodies in that they bind tightly to a specific chosen molecule. In this case, the aptamers were designed to bind to ATP as well as to the surface of gold nanoparticles. These aptamers were also equipped with a reporter molecule that is capable of producing a bright fluorescent signal.

The key to the nanoflare’s unique signaling ability lies in the fact that gold nanoparticles will quench, or prevent, the reporter molecule from emitting its light signal when the attached aptamer is stuck to the nanoparticle. However, when ATP is present, it causes the aptamer to change shape, releasing it from the nanoparticle and allowing the reporter molecule to fluoresce. The amount of aptamer released from the nanoparticle, and hence the intensity of the fluorescent signal, is directly proportional to the amount of ATP present in a cell.

Cells growing in culture rapidly take up the aptamer-coated nanoparticle and soon begin to fluoresce brightly. Then, when the cells are treated with a drug combination known to cause a cell to use up its ATP stores, the fluorescence begins dimming in a dose-dependent manner. Thanks to well-established methods for developing aptamers that will bind to specific biomolecules, it is likely that nanoflares will become a versatile new tool for use in a variety of intracellular processes.

This work, which is detailed in the paper “Aptamer nanoflares for molecular detection in living cells,” was supported by the NCI Alliance for Nanotechnology in Cancer, a comprehensive initiative designed to accelerate the application of nanotechnology to the prevention, diagnosis, and treatment of cancer. An abstract is available at the journal’s Web site. View abstract