DNA Field Effect Transistor

The human genome project has accentuated the need for rapid identification of the expression of particular genes in particular cells or organisms. The most promising technology for parallel detection being based on so called "genechips", consisting of an array of many thousand spots of oligonucleotides, each corresponding to a unique DNA sequence attached to a solid substrate. Using fluorescently labeled target DNA, hybridizations related to gene expressions can be detectedAutomated systems using this method are commercially available. They utilize automated image analysis of the illuminated, hybridized arrays to generate a map of the location of the hybridized DNA, and thus identify the target DNA. This approach is indirect. The optical readout step must be followed by image analysis and processing before the target DNA is identified, greatly complicating the readout process. The technique also requires labeling of target DNA. With proper design, a similar approach could be developed electronically if the conducting channel could be exposed so that oligonucleotides could be attached, and changes in charge density detected as hybridization is carried out with target molecules. Researchers at Arizona State University have indeed devised a system for direct, electronic detection of biopolymer binding, such as DNA hybridization, compatible with the solution chemistry required for carrying out the binding. It eliminates the need of labeling of either the probe or target DNA. It is also compatible with exposure to solutions both for attachment of DNA and for subsequent detection of hybridization. The need for such a device, in fact, goes beyond DNA hybridization. Any interaction that changes the charge associated with a biopolymer could be detected by such a device. Examples would be changes in oxidation state of redox protein or binding by one polypeptide to another where there is a net change of charge.