The ability to synthesize oligonucleotides with specific sequences using phosphoramidite chemistry has revolutionized molecular diagnostics. Here are some examples of how oligonucleotides are used in diagnostics:

Polymerase Chain Reaction (PCR): PCR is a technique used to amplify a specific DNA sequence. Oligonucleotides called primers are used to initiate DNA synthesis at the flanking regions of the target sequence.

Southern Blotting: Southern blotting is a technique used to detect specific DNA sequences in a sample. Oligonucleotides called probes are used to bind to the target DNA sequence by complementary base pairing.

Northern Blotting: Northern blotting is similar to Southern blotting, but it is used to detect specific RNA sequences.

Western Blotting: Western blotting is used to detect specific proteins in a sample. While not directly involving oligonucleotides, some western blot techniques utilize oligonucleotide probes labelled with antibodies for signal amplification.

In Situ Hybridization (ISH): ISH is a technique used to visualize the location of specific DNA or RNA sequences within cells or tissues. Oligonucleotide probes are used to bind to the target sequence and are then visualized using a fluorescent label.

DNA Microarrays: DNA microarrays are used to analyze the expression of thousands of genes simultaneously. Oligonucleotides are spotted onto a solid surface in a high-density array, and then the sample being analyzed is hybridized to the array. The pattern of hybridization can be used to identify genes that are differentially expressed.