Molecular probes are small DNA segments (genomic DNA, cDNA or synthetic oligonucleotides) or RNA segments (often synthesized on DNA template) that recognize complementary sequences in DNA or RNA molecules and thus allow identification and isolation of these specific DNA sequences from an organism. Antibodies are also occasionally use as probes to recognize specific protein sequences. These probes also frequently used for a variety of other purposes including diagnosis of infectious diseases, identification of food contaminants, variety of microbiological tests, forensic tests (e.g. fingerprinting of murderers or rapists), etc. Probes can also be used to identify strains of an organism e.g. varieties of a crop species (a plant breeder likes to have quick test to identify his variety to maintain his patent or breeder's right, so that a competitor may not use it in another name leading to infringement of rights).
DNA/RNA probe assays are faster and sensitive, so that many conventional diagnostic tests for viruses and bacteria involving culturing of the organism, are being fast replaced by antibody and DNA probe assays. While culture tests can take days or even months, molecular probe assays can be performed within few hours or minutes. Therefore, the use of DNA probes has become today's most sophisticated and sensitive technology for a variety of uses involving biological systems both in basic and applied studies including their commercial use.