Detection of three trace chromatin immunoprecipitate 454 single-stranded DNA libraries prepared from ~1.2 ng input mouse chromatin by digital PCR. A No signal from libraries on the NanoDrop spectrophotometer or the Agilent Bioanalyzer capillary electrophoresis unit. The two signals appearing in the electropherograms are molecular weight markers of 15 bp and 1500 bp. B Detection of library molecules by digital PCR. False-color image of 12.765 digital array at assay endpoint. Each grid point corresponds to a nanoliter-scale PCR reaction, with yellow squares revealing amplification due to the presence of at least one sequencing library template molecule. The panels show dilution series (indicated) of samples analyzed in part A, allowing accurate absolute quantification of the samples by UT digital PCR.