London, July 1 : Researchers at the U.S. Department of Energy's Lawrence Berkeley National Laboratory (Berkeley Lab) claim to have invented a simple and inexpensive method for reading DNA (or RNA) microarrays within minutes.
The researchers have revealed that their technique is based on measuring the electrostatic repulsion between silica microspheres and hybridised DNA.
The significance of their work lies in the fact that it takes scientists a step closer to realising the dream of expanding personalized medicines beyond the wealthiest of nations with state-of-the-art clinics.
The researchers say that their technique is so simple that it can be carried out in a matter of minutes.
"One of the most amazing things about our electrostatic detection method is that it requires nothing more than the naked eye to read out results that currently require chemical labeling and confocal laser scanners," Nature magazine quoted led researcher Jay Groves, a chemist with joint appointments at Berkeley Lab's Physical Biosciences Division and the Chemistry Department of the University of California (UC) at Berkeley, as saying.
"We believe this technique could revolutionize the use of DNA microarrays for both research and diagnostics," he added.
In their research paper, Groves and his colleagues describe how dispersing a fluid containing thousands of electrically-charged microscopic beads or spheres made of silica (glass) across the surface of a DNA microarray, and then observing the Brownian motion of the spheres provided measurements of the electrical charges of the DNA molecules.
The researchers say that such measurements can in turn be used to interrogate millions of DNA sequences at a time.
According to them, such measurements can be observed and recorded with a simple hand-held imaging device, and that even a cell phone camera would do.
"The assumption has been that no detection technique could be more sensitive than fluorescent labeling, but this is completely untrue, as our results have plainly demonstrated," said Groves.
"We've shown that changes in surface charge density as a result of specific DNA hybridization can be detected and quantified with 50-picomolar sensitivity, single base-pair mismatch selectivity, and in the presence of complex backgrounds. Furthermore, our electrostatic detection technique should render DNA and RNA microarrays sufficiently cost effective for broad world-health applications, as well as research," he added.
The use of DNA microarray assays has so far been limited because current techniques typically depend upon fluorescence detection, a demanding methodology that requires time-consuming chemical labelling, high-power excitation sources, and sophisticated instrumentation for scanning.
Individual laboratories or clinics, especially in developing countries, can't afford such a methodology.
While label-free DNA detection strategies do exist, they require either complex device fabrication or sophisticated instrumentation for readouts, and in addition none are compatible with conventional DNA microarrays, where up to one million sequences are available for interrogation in a single experiment.
"We have demonstrated parallel sampling of a microarray surface with micron-scale resolutions over centimetre-scale lengths. This is four orders of magnitude larger than what has been achieved to date with conventional scanning-electrostatic-force microscopy," said Groves.
The researchers have revealed that they are planning to test the application of their technique in high-density arrays, and pushing its ultimate resolution limits.
"Since the resolution of electrostatic-based imaging is determined by the number of particle-observations rather than by the diffraction limit of light, our readouts could serve as a form of ultramicroscopy. The real grand challenge for this technology, however, will be for us to find suitable industrial partners with whom we can work to see that useful new products actually make it to market," Groves said.