Scientists, including one of Indian origin, have developed tiny electronic "tweezers" using graphene that can efficiently grab biomolecules floating in water, an advance that may lead to a handheld disease detecting system. Graphene, a material made of a single layer of carbon atoms, was discovered more than a decade ago and has enthralled researchers with its range of amazing properties that have found uses in many new applications from microelectronics to solar cells. The graphene tweezers developed at the University of Minnesota in the US are vastly more effective at trapping particles compared to other techniques used in the past due to the fact that graphene is a single atom thick, less than one billionth of a metre. The physical principle of tweezing or trapping nanometre-scale objects, known as dielectrophoresis, has been known for a long time and is typically practiced by using a pair of metal electrodes. From the viewpoint of grabbing molecules, however, metal electrodes are very blunt. They simply lack the "sharpness" to pick up and control nanometre-scale objects. "Graphene is the thinnest material ever discovered, and it is this property that allows us to make these tweezers so efficient.
No other material can come close," said Sang-Hyun Oh, professor at the University of Minnesota. "To build efficient electronic tweezers to grab biomolecules, basically we need to create miniaturised lightning rods and concentrate huge amount of electrical flux on the sharp tip. The edges of graphene are the sharpest lightning rods," said Oh. The team also showed that the graphene tweezers could be used for a wide range of physical and biological applications by trapping semiconductor nanocrystals, nanodiamond particles, and even DNA molecules. Normally this type of trapping would require high voltages, restricting it to a laboratory environment, but graphene tweezers can trap small DNA molecules at around one Volt, meaning that this could work on portable devices such as mobile phones. Researchers made the graphene tweezers by creating a sandwich structure where a thin insulating material call hafnium dioxide is sandwiched between a metal electrode on one side and graphene on the other. Hafnium dioxide is a material that is commonly used in today's advanced microchips. "One of the great things about graphene is it is compatible with standard processing tools in the semiconductor industry, which will make it much easier to commercialise these devices in the future," said Koester, who led the effort to fabricate the graphene devices. "Since we are the first to demonstrate such low-power trapping of biomolecules using graphene tweezers, more work still needs to be done to determine the theoretical limits for a fully optimised device," said Avijit Barik, graduate student at University of Minnesota. "For this initial demonstration, we have used sophisticated laboratory tools such as a fluorescence microscope and electronic instruments," said Barik, lead author of the study published in Nature Communications. "Our ultimate goal is to miniaturise the entire apparatus into a single microchip that is operated by a mobile phone," he said.
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