UCLA chemists create Nano Valve
and closed at will to trap and release molecules. The nano valve
could potentially be used as a drug delivery system, trapping and
releasing therapeutic molecules on demand.
Conventional forms of drug administration generally rely on pills, eye drops, ointments, and intravenous solutions. Recently, a number of novel drug delivery approaches have been developed.
These approaches include drug modification by chemical means, drug entrapment in small vesicles that are injected into the bloodstream, and drug entrapment within pumps or polymeric materials that are placed in desired bodily compartments (for example, the eye or beneath the skin). These techniques have already led to delivery systems that improve human health, and continued research may revolutionise the way many drugs are delivered.
The valve is designed so one end attaches to the opening of the hole that will be blocked and unblocked, and the other end has the switchable rotaxanes whose movable component blocks the hole in the down position and leaves it open in the up position.
Switchable rotaxanes are molecules composed of a dumbbell component with two stations between which a ring component can be made to move back and forth in a linear fashion.
The researchers used chemical energy involving a single electron as the power supply to open and shut the valve, and a luminescent molecule that allows them to tell from emitted light whether a molecule is trapped or has been released.
UCLA scientists have shown how these switchable rotaxanes can be used in molecular electronics. The team is now adapting them for use in the construction of artificial molecular machinery.
"This paper demonstrates the machine works," said Jeffrey Zink, a UCLA professor of chemistry and biochemistry." With the nano valve, we are able to control molecules at the nano scale."
"The valve is like a mechanical system that we can control like a water faucet," said UCLA graduate student Thoi Nguyen, lead author on the paper. "Trapping the molecule inside and shutting the valve tightly was a challenge. The first valves we produced leaked slightly."
This nano valve consists of moving parts, switchable rotaxane molecules that resemble linear motors designed by California NanoSystems Institute director Fraser Stoddart's team, attached to a tiny piece of glass (porous silica), which measures about 500 nanometers, and which Nguyen is currently reducing in size. Tiny pores in the glass are only a few nanometers in size.
"It's big enough to let molecules in and out, but small enough so that the switchable rotaxane molecules can block the hole," Zink added.
This research is significant, as scientists have taken a bistable molecule that behaves as a switch in a silicon-based electronic device at the nanoscale level and have fabricated it differently to work as part of a nano valve on porous silica.
"It shows that these little pieces of molecular machinery are highly adaptable and resourceful, and means that we can move around in the nanoworld with the same molecular tool kit and adapt it to different needs on demand," said California NanoSystems Institute director Fraser Stoddart.
Stoddart mentioned that in future research, they would test how large a hole they can block, to see whether they can get larger molecules, like enzymes, inside the container.
