Biochips are microscopic slides (generally made of glass or a polymer) on which biological material (e.g. oligonucleotides or cDNA) is fixed in large numbers and with a high density, as a single strand in the form of microarrays, i.e. in a defined arrangement.
Such chips perform the function of diagnostic tools and are offered by many manufacturers with various attributes.
In the case of biochip analysis, the substance under investigation, which is also single-strand (e.g. a patient sample or food sample), is brought into contact with the molecules fixed on the chip. If molecules of the sample substance encounter molecules of the chip that are complementary to them, an interaction occurs on the basis of the key-and-lock principle ("precise-fit mating parts"), with formation of a double strand (complementary hybridization). This process can be visualized by appropriate pretreatment of the sample materials with fluorescent dye. The fluorescent pattern thus produced contains the information as to what substances were present in the sample.