Handheld DNA detector

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Handheld DNA detector

http://www.eurekalert.org/pub_releases/2008-03/ip-hdd031008.php

A researcher at the National University at San Diego has taken a

mathematical approach to a biological problem - how to design a

portable DNA detector. Writing in the International Journal of

Nanotechnology, he describes a mathematical simulation to show how a

new type of nanoscale transistor might be coupled to a DNA sensor

system to produce a characteristic signal for specific DNA fragments

in a sample.

Afuwape of the National University, in San Diego, California,

explains that a portable DNA sequencer could make life easier for

environmental scientists testing contaminated sites. Clinicians and

medical researchers too could use it to diagnose genetic disorders

and study problems in genetics. Such a sensor might also be used to

spot the weapons of the bioterrorist or in criminal forensic

investigations.

The earliest DNA biosensors used fluorescent labels to target DNA,

but these were expensive and slow. The next generation used mediator

molecules to speed up the process and labeled enzymes to make the

sensors highly selective for their target molecules. None of these

systems were portable, however, and the current research trend is

towards systems that use no molecular labels and have avoid costly

reagents.

Nevertheless, DNA biosensors are already becoming ubiquitous in many

areas, but the instrumentation is usually limited to the laboratory

setting. Afuwape says that a commercially viable, off-the-shelf

handheld DNA biosensor that could be used in environmental, medical,

forensics and other applications might be possible if researchers

could unravel the basic molecular machinery operating at the

interface between sample and detector.

Afuwape suggests that a new type of electronic device, the ion-

selective field-effect transistor (ISFET), might be integrated into a

DNA biosensor. Such a sensor would be coated with thousands of known

DNA sequences that could match up - hybridize - with specific DNA

fragments in a given medical or environmental sample.

The key to making the system work is that the ISFET can measure

changes in conductivity. Constructing a sensor so that the process of

DNA hybridization is coupled to a chemical reaction that generates

electricity would produce discrete electronics signals. These signals

would be picked up by the ISFET. The characteristic pattern of the

signals would correspond to hybridization of a known DNA sequence on

the sensor and so could reveal the presence of its counterpart DNA in

the sample. Afuwape's mathematical work demonstrates that various

known chemical reaction circuits involving DNA could be exploited in

such a sensor.

" The ISFET is proving to be a powerful platform on which to design

and develop selective, sensitive, and fast miniature DNA sensors, "

says Afuwape, " such portable DNA sensors will find broad application

in medical, agriculture, environmental and bioweapons detection. "