Array sensitivity determined by control probe signal intensity values. Human genomic DNA spiked with 70-mer oligonucleotides at different concentrations was compared against the same sample without oligonucleotides. Normalized signal intensity values from the Cy3 channel were plotted on a log scale and compared using linear regression from human genomic DNA samples with and without 70-mer oligonucleotides spiked into the labelling reaction. The probes being assessed on this scatter plot are perfect matches to the 70-mer oligonucleotide sequence. Each notation on the graph represents a specific concentration of spiked-in 70-mer oligonucleotides on an individual array. The oligonucleotides were spiked into the labelling reaction at a concentration range from 4.5 pM to 364 pM. The divergence of R2 value from that with no spike-in was used to measure the sensitivity of detection on the array.