Molecular chopsticks

时间:2019-03-07 08:12:01166网络整理admin

By Sharon-Ann Holgate A NEW tool has arrived for engineers of the seriously small: a reliable pair of nanotweezers. One day the device could let researchers manipulate biological cells, construct nanomachines, perform microsurgery—even grip individual molecules. The experimental tweezers, whose working end is a pair of electrically controlled carbon nanotubes, were developed by Philip Kim and Charles Lieber from Harvard University. Using the tool, they have successfully grasped clusters of polystyrene spheres of around 500 nanometres in diameter—the same scale as cellular substructures. They were also able to remove a semiconductor wire 20 nanometres wide from a mass of entangled wires. The team says that because carbon nanotubes are not only very strong but also good conductors of electricity, the tweezers could also be used to measure the electrical characteristics, such as resistance, of nanostructures within their grasp. They could analyse microcircuits or even the components of future nanorobots that might perform surgery inside the body. The tweezers were made by depositing gold electrodes on either side of a tapered glass micropipette 100 nanometres across (see Diagram). The tweezer’s arms were each made of a bundle of multiwalled carbon nanotubes or buckytubes—cylindrical versions of the famous buckyball, arranged concentrically like the layers of an onion. One of these was then glued with a conductive adhesive to each electrode. To operate the tweezers, a voltage is applied across the electrodes, causing one nanotube arm to develop a positive electrostatic charge and the other to develop a negative charge. The attractive force can be increased or decreased by varying the applied voltage. The team found that they could completely close the arms at a voltage of 8.5 volts, while lower voltages would give certain degrees of grip. At present, each of the tweezer’s arms is about 50 nanometres wide and 4 micrometres long. But by growing single-walled nanotubes directly onto the electrodes, the researchers hope to produce tweezers small enough to grab individual molecules. Japanese researchers have already designed a pair of chemical tweezers that can pick up one molecule at a time (New Scientist, 17 August 1996, p 22) but their device could only recognise and clamp tightly to one particular type of molecule, such as a sugar molecule. They are not designed to be general purpose,