Nanoneedle built with carbon nanotubes

Michael A. Greenwood

Researchers seeking to create a biological delivery system that causes minimal cell damage have devised a working nanoinjector that is constructed from carbon nanotubes and guided by a precision microscope.

he device can deposit discrete cargos at different sites within a cell — perhaps even within specific organelles — something existing delivery systems cannot do, the researchers said. An added benefit is that the nanoinjector does not require a carrier solvent.

The delivery technique offers precision temporal and spatial control, and it caused no discernible cell damage during experiments. It is designed to inject smaller cells, potentially even bacteria, and could open the door for studies of intracellular processes. The injection method also might be used for medical procedures such as in vitro fertilization.

Although several other methods exist to convey exogenous materials into a cell — permeabilization of the membrane with lipids, electric currents, pore-forming toxins and micropipettes — each has the potential to damage a cell’s membrane, or even to kill the cell, according to the researchers from the University of California and from the Lawrence Berkeley National Laboratory, both in Berkeley.

The carbon nanotubes range in size from 1 to 20 nm — a scale that enables them to penetrate a cell’s membrane without any discernible damage, said the investigators, led by Carolyn R. Bertozzi. Indeed, the breach created by the penetration is about the size of a single protein’s diameter and is likely to heal by the process of lipid diffusion.

The nanoinjector was created with a single multiwalled carbon nanotube that was attached to the tip of an atomic force microscope. This setup allowed precision positioning of the needle and a high degree of sensitivity when piercing a cell membrane.

Delivery into cytosol

To test the device, researchers sought to deliver quantum dots into a cell’s cytosol without causing damage. Without appropriate delivery systems, quantum dots cannot be introduced into the cytosol or nuclei.

The nanoinjector’s tip was loaded with quantum dots and injected into a human cervical epithelial cancer cell line. The cell was imaged with fluorescence microscopy, and the presence of quantum dots within the confines of the cell was confirmed with video microscopy analysis.

The nanoneedle is shown as it appeared before it was loaded with quantum dots (A and B) and after (C). Reprinted with permission of PNAS.

To see whether the membranes and cells were damaged as a result of the injection, the scientists used three assays to determine the effect of the nanoneedle and found no evidence of compromised membranes. In some cases, the nanoneedle was kept inside the cell for more than an hour.

In addition to quantum dots, the researchers said that the nanoneedle could be used to deliver other biomolecules, including DNA, RNA and polymers.

One drawback is that the nanoneedle system currently requires highly sophisticated instrumentation and expertise to prepare and operate. The researchers used a scanning electron microscope equipped with a manipulator to put a carbon nanotube on the tip of an atomic force microscope combined with a fluorescence microscope. Bertozzi said that further research is needed to simplify the technique before it can become standardized and commercialized for widespread use.

PNAS, May 15, 2007, Vol. 104, pp. 8218-8222.