Recommended reading: Climate Change and Microbial Ecology | Polymerase Chain Reaction | SUMOylation and UbiquitinationDNA oligonucleotides are spotted onto the array. The main feature of oligonucleotide microarrays is that each gene is normally represented by more than one probe.
Spotted microarraysIn spotted microarrays technology, oligonucleotides, cDNA or small fragments of PCR products corresponding to specific genes are spotted on the chip. A robot spotter normally does the process and one or more probes can be used for each gene.
Contrary to oligonucleotide arrays, spotted arrays are "customizable"; the user can choose the probes to be spotted according to specific experimental needs. These kinds of arrays are usually hybridized with labeled cDNA and allow double channel hybridization experiments: two cDNA samples can be labeled with two different fluorophores (e.g. Cy3 and Cy5); these are mixed together and hybridized to the same chip. After washing, the chip is scanned at different wavelengths, thus allowing the measurement of the two samples in one run.