Different microarray technologies have been developed that can be divided into three categories: spotted cDNA microarrays, spotted oligonucleotide microarrays, and Affymetrix chips.
Spotted cDNA and oligonucleotide microarrays include both contact printing and the newer ink-jet technology (a wonderful spin-off; originally invented to deal with the
delicate task of stamping dates on eggs without breaking the eggshells). They may be spotted onto glass slides, in which case laser fluorescence may be used to detect two-color hybridization from two samples at once. Or they may be spotted, rather more cheaply, onto filters, in which case radiolabelled material is used for hybridization, one sample at a time. One maker's slide arrays are generally compatible with another
manufacturer's laser fluorescence analysis system; similarly, filters can be read by any scanner. There remain the very wonderful Affymetrix chips, manufactured in a unique way, and only readable with a special Affymetrix machine which cannot be used on any other maker's arrays; these can be regarded as a distinct subtype.