A modified nanoscale transistor could dramatically speed up the detection of DNA sequences, according to US researchers.
The detector consists of a quantum dot with a piece of DNA attached. It only allows current to flow when a matching sequence of DNA binds to the attached piece and could provide a simple, faster way to detect viruses or to track gene expression.
Researchers at Quantum Logic Devices, in Texas, US, constructed the detector by modifying an existing transistor design. This features a 5-nanometre-wide gold particle flanked by three electrodes.
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One of the electrodes switches the transistor on and off while the other two connect it to a larger circuit. The researchers simply removed the controlling electrode and attached a 36-letters-long sequence of DNA to the particle instead. Attaching the DNA molecule means that the device now switches on and off when a matching sequence of DNA becomes attached.
Digital signal
鈥淭he bonds that form between the two strands shift charge around a little and corresponding charge is induced in the quantum dot,鈥� explains Louis Brousseau, CEO of Quantum Logic Devices and lead researcher on the project. This switches the current on and off to create a 鈥渄igital signal,鈥� he adds.
Brousseau believes the technique could accelerate medical research and the detection of dangerous pathogens. 鈥淩esearchers currently label DNA molecules using fluorescence, but that can take around 24 hours to produce a result,鈥� he says.
The new detector can detect a piece of DNA in less than 30 minutes. 鈥淭he many variables of current procedures make interpretation more art than science,鈥� Brousseau adds. 鈥淭his way produces much more clear-cut results.鈥�
He thinks the detector would be ideal for diagnosing viruses quickly. 鈥淭hey can replicate very fast so you want to know if someone is infected quickly,鈥� he says. 鈥淲aiting 24 hours can miss the critical period.鈥�
Cruddy interference
Sub Reddy, a biosensor expert at Surrey University in the UK, says the detectors should be extremely sensitive. 鈥淚t can detect a single matching sequence, while current methods record the aggregate of many such events,鈥� he notes. 鈥淚t鈥檚 usually necessary to amplify the DNA in a sample to get a signal, but you could cut that out and perhaps use it in on samples in the field.鈥�
However, Reddy also sees some drawbacks. 鈥淪ample purity becomes important, if you鈥檝e got one bit of crud in there it could interfere,鈥� he warns.
The team at Quantum Logic Devices are currently developing a chip containing thousands of individual quantum dot transistors, manufactured using conventional semiconductor technologies. These could keep track of levels of combinations of genes in a biological sample, Brousseau says.
Journal reference: Journal of the American Chemical Society (DOI: 10.1021/ja063022f)
