Signal intensities of probes. Signal intensities of random probes as a function of probe length in the 7 levels of target oligodeoxyribonucleotide concentration range of 1.4 fM to 1.4 nM. The signal intensities of PM probes were averaged over three PM probes and those of MM probes are represented by the average of the mismatch probes the center bases of which were substituted to all other nucleotides. Solid and dashed lines correspond to signal intensities of PM and MM probes, respectively. Standard deviations are given in additional file 2.