BIOCHIPS, A TRENDING TEHCNIQUE

In molecular biology, biochips are essentially miniaturized laboratories that can perform hundreds or thousands of simultaneous biochemical reactions. Biochips enable researchers to quickly screen large numbers of biological analytes for a variety of purposes, from disease diagnosis to detection of bioterrorism agents.The development started with early work on the underlying sensor technology. One of the first portable chemistry-based sensors was the glass pH electrode, invented in 1922 by Hughes (Hughes, 1922). Measurement of pH was accomplished by detecting the potential difference developed across a thin glass membrane selective to the permeation of hydrogen ions; this selectivity was achieved by exchanges between H+ and SiO sites in the glass. The basic concept of using exchange sites to create permselective membranes was used to develop other ion sensors in subsequent years. For example, a K+ sensor was produced by incorporating valinomycin into a thin membrane (Schultz, 1996). Over thirty years elapsed before the first true biosensor (i.e. a sensor utilizing biological molecules) emerged. In 1956, Leland Clark published a paper on an oxygen sensing electrode (Clark, 1956_41). This device became the basis for a glucose sensor developed in 1962 by Clark and colleague Lyons which utilized glucose oxidase molecules embedded in a dialysis membrane (Clark, 1962). The enzyme functioned in the presence of glucose to decrease the amount of oxygen available to the oxygen electrode, thereby relating oxygen levels to glucose concentration. This and similar biosensors became known as enzyme electrodes, and are still in use today.
Today, a large variety of biochip technologies are either in development or being commercialized. Numerous advancements continue to be made in sensing research that enable new platforms to be developed for new applications. Cancer diagnosis through DNA typing is just one market opportunity. A variety of industries currently desire the ability to simultaneously screen for a wide range of chemical and biological agents, with purposes ranging from testing public water systems for disease agents to screening airline cargo for explosives. Pharmaceutical companies wish to combinatorially screen drug candidates against target enzymes. To achieve these ends, DNA, RNA, proteins, and even living cells are being employed as sensing mediators on biochips . Numerous transduction methods can be employed including surface plasmon resonance,fluorescence, and chemiluminescence. The particular sensing and transduction techniques chosen depend on factors such as price, sensitivity, and reusability.