A biochip consists of a tiny substrate of glass or silicon covered with bits of DNA. When a specimen of diseased tissue is dropped on a biochip, the device locates the active genes, the first important step towards diagnosis and treatment. In a few years, some say, biochips could be routine diagnostic tools in hospitals.

   "Biochips, which were first introduced by Santa Clara's Affymetrix Inc. in the mid-1990s, show how high tech and biotech have worked together to translate DNA's chemical code into electronic data that can be studied and stored".

    It is amazing that every human cell contains the complete genome. But only a few hundred to a few thousand genes are active in any given cell at any given time. The rest lay dormant.

    This is the ultimate goal of medicine; to figure out which genes should be active to keep cells healthy and to detect the inappropriate gene activity that makes cells sick.

    Biochips are designed to make that distinction and meet that goal. They work by taking advantage of DNA's nature. DNA is double stranded, like a zipper. In order for DNA to perform any  action, it must first unzip to create single stranded mRNA. This mRNA is ambitious and has one purpose -- to find its exact opposite and bind to it, becoming double stranded once again.

    Biochips are built to take advantage of single-stranded mRNA. Their surface is covered with single-stranded bits of DNA, representing a unique fragment of some gene. Each bit is about the diameter of a human hair. With the same technology used to etch electronic paths onto silicon biochips, scientists can put up to 400,000 gene bits in a precise pattern. From the air, the biochip might resemble a hair brush.

    Though they're made like computer chips, biochips don't perform calculations. The main objective of the biochip is to detect active genes. To put biochips to work, scientists first extract the mRNA -- the active version of the gene -- from the cell being studied or analyzed. They add a fluorescent dye to the extract, then drop the dyed specimen directly onto the surface of the biochip.

    The mRNA sort of hovers over the biochip until all the mRNA has bound to a strand on the chip's surface. The biochip is scanned by a laser that detects the fluorescent tags and shows which of the 400,000 or so bits received mRNAs. Based on the scanner results, custom software figures out which genes are active. By repeating such experiments thousands of times, comparing healthy and sick cells, scientists have detected patterns that have led to more than 300 scientific publications. These experiments have also started a wave of drug discovery efforts.

    As of now, when a patient shows signs of pneumonia, doctors have no way to know whether it's viral or bacterial, and whether it would respond to a given medication. If the genes for known strains of pneumonia were put on a biochip, it would only take an hour or so to diagnose the type of infection and the best suited form of treatment.