A test that can detect hundreds of thousands of different fragments of DNA sequences, proteins or antibodies could be built onto a tiny silicon chip. Researchers say the technology could lead to devices for medical diagnostics or environmental monitoring.
at Stanford University in California and his colleagues created a metamaterial from silicon that can identify gene fragments just 22 nucleotides long within 5 minutes. When a sample is placed on the chip and near-infrared light is shone on one side of the material, microscopic antennae focus it onto specific spots on the other side that each correspond to a positive test for a different fragment.
A square centimetre of this metamaterial can have more than 200,000 of these spots that recognise different molecules. Although the spots of light would be impossible to detect with the human eye, they can be monitored with a camera sensor to provide virtually instantaneous detection.
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Existing PCR tests rely on replicating DNA strands in a sample so that reactions between gene fragments and dyes occur in sufficient quantity that the products are visible to the naked eye. This replication can take hours, and the process involves several steps at a dedicated laboratory.
With the metamaterial test, the amplification isn鈥檛 done on the DNA side, but on the display side. If a DNA fragment being tested for is present, it interacts with one of the antennae and causes it to focus incoming light into a very narrow beam that is detected on the other side of the chip as a positive result.
This makes it much faster than PCR tests: it can return results within minutes, and requires no intermediate steps and no specialist laboratory.
at Washington University in St. Louis, Missouri, a member of the study team, says: 鈥淧CR harnesses chemistry to amplify the amount of biological stuff, and then makes the optical signal superstrong so that it鈥檚 easy to detect. We take the opposite approach of amplifying the optical signal from a very small amount of biological stuff.鈥�
The metamaterial is made in silicon using techniques from the computer chip- manufacturing industry, so it could potentially be created cheaply and at scale, and easily incorporated into electrical devices.
While their initial focus was on DNA testing, the researchers say the technique should be applicable to a range of biomolecules that PCR tests and other tests aren鈥檛 capable of detecting, including proteins and metabolites. This means they could be useful in medicine, but also in monitoring seas, lakes and other ecosystems.
Hu says millions of the nano-antennae that focus light from different reactions could be put into a single chip, and could potentially create a single, universal medical sensor.
鈥淚n biological systems, there are millions and billions of different kinds of signals, or information contained in different kind of biomarkers, and generally the way we probe them now is kind of like trying to piece together a lot of disparate assays and tests to try to put together a picture of someone鈥檚 holistic health,鈥� he says. 鈥淏ut I think [that with] these technologies, you start to be able to put together a lot of these assays into one device.鈥�
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