Principles of Fluorescence Spectroscopy

734 DNA TECHNOLOGY
Figure 21.60. Analysis of gene expression using a spotted DNA
microarray. Revised from [185].
it is possible to study how families of genes are activated in
response to stimuli or at different phases of the growth
cycle.
21.9.2. Light-Generated DNA Arrays
DNA arrays can also be made using a combination of photochemistry
and photolithography. 187–189 This approach is
shown in Figure 21.63. The surface is coated with a protected
hydroxyl groups. Regions of the surface are deprotected
by light and coupled to a nucleotide. Another region of the
surface is then deprotected and another nucleotide is added.
This process is repeated until the oligomers are 15 to 25
bases long. Up to 300,000 oligonucleotides can be synthesized
and located in a 1.28 x 1.28 cm array. Typically a single
gene is represented by about 20 oligomers. These lightgenerated
arrays are manufactured by Affymetrix Inc. Gene
chips are available for a number of organisms. It appears
that the expression levels are determined by intensities at a
single wavelength rather than by intensity ratios for different
wavelengths. Light-generated arrays can also be made
using micromirror arrays or digital light processors. 190–191
Figure 21.61. Color image of portion of a DNA array. The lower
panel shows the intensity profiles of Cy3 (green) and Cy5 (red) across
one row of the array. From [178].
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