We analyze a series of controlled experiments on DNA microarrays 
produced by Affymetrix. In these experiments some genes are added in solution
at known concentration according to a Latin square scheme. We show that 
the data can be fitted very well by a simple Langmuir model which takes 
into account

1) the hybridization (=binding) of sequences in solution with complementary
sequences anchored at the microarray surface and 
2) the hybridization of partially complementary sequences in solution. 

When appropriately rescaled the data collapse into a single master curve.

A reprint of our recent paper Physica A 362, 433 (2006) can be found here:
http://www.iri.cnrs.fr/bn/pubs/enrico/physicaA06.pdf