A nanometer-scale probe designed to slip into a cell wall and fuse with it could offer researchers a portal for extended eavesdropping on the inner electrical activity of individual cells.

Everything from signals generated as cells communicate with each other to “digestive rumblings” as cells react to medication could be monitored for up to a week, say the Stanford engineers.

Current methods of probing a cell are so destructive they usually only allow a few hours of observation before the cell dies. The researchers are the first to implant an inorganic device into a cell wall without damaging it.

The key design feature of the probe is that it mimics natural gateways in the cell membrane, said Nick Melosh, an assistant professor of materials science and engineering in whose lab the research was done. With modification, the probe might serve as a conduit for inserting medication into a cell's heavily defended interior, he said. It might also provide an improved method of attaching neural prosthetics, such as artificial arms that are controlled by pectoral muscles, or deep brain implants used for treating depression.

The 600-nanometer-long, metal-coated silicon probe has integrated so smoothly into membranes in the laboratory, the researchers have christened it the “stealth” probe.

“The probes fuse into the membranes spontaneously and form good, strong junctions there,” Melosh said. The attachment is so strong, he said, “We cannot pull them out. The membrane will just keep deforming rather than let go of the probes.”

The key to the probe's easy insertion – and the membrane's desire to retain it – is that Melosh and Almquist based its design on a type of protein naturally found in cell walls that acts as a gatekeeper, controlling which molecules are allowed in or out.

A cell membrane is essentially a walled fortress. Within the wall itself is a water-repellant, or hydrophobic, zone. Since almost all molecules in a living being are water soluble, the hydrophobic region acts as a barrier to keep the molecules from slipping through the cell wall. The only way in or out is via the specialized proteins that form bridges across the membrane.

Those “transmembrane” protein gateways match the architecture of the membrane, with a hydrophobic center section bounded by two water soluble, or hydrophilic, layers.

“What we have done is make an inorganic version of one of those membrane proteins, which sits in the membrane without disrupting it,” Melosh said. “Now we can envision using it for doing our own gate keeping.”