Virus and chips

How clean is that surface?

A highly sensitive detector for viral nucleic acids has been developed by Israeli scientists for use in food quality control, medical diagnostics and in environmental testing. The system allows for reliable testing of a wide variety of pathogens without the need for high throughput techniques.

Itamar Willner and Moshe Kotler of the Hebrew University of Jerusalem believe that current approaches to pathogen detection based on DNA chips have several disadvantages. These systems reveal the presence of bacteria and viruses by spotting their telltale genetic fingerprints but analysis requires amplification of the nucleic acids as well as a solid surface on which detection takes place.

	Itamar Willner

Willner, Kotler and colleagues have now sidestepped this ungainly approach to detection by detecting viruses electrically instead. "Our new process is suited to a broad application in biochip technology," Willner says. The device is based on a piezoelectric crystal electrode attached to a gold surface to which strands of nucleic acid complementary to viral RNA are anchored. If the viral RNA is present, then an enzyme reaction is initiated to build up the complete complement. The replication introduces tagged nucleic acids into the complementary replica. A second enzyme, alkaline phosphatase, then binds to the tags and this catalyses the precipitation of an insoluble indigo product on the crystal.

Viral detection simplified. Click on picture to enlarge view.

The final, detection, step involves simply observing the change in vibrational frequency of the piezoelectric crystal with the extra weight of indigo-enzyme precipitate on-board. Any change indicates the presence of indigo on the crystal surface and so logically the presence of viral RNA in the original sample. The lower frequency due to the additional mass, however, also correlates with the concentration of virus. This provides the team with a quantitative means of determining the presence of the virus.

Willner and his colleagues have detected the presence of just 60 viral particles in this way in a single droplet of just ten microliters. In the same paper, they also describe the use of an electrode, and the electrochemical detection of viral nucleic acids by a similar detection protocol to that used in the piezoelectric measurements.

Source:
Angew. Chem. Int. Ed. 2001, 40, 2261.