The DNA microarray limit of detection (LOD). LOD for Rickettsia spp., Coxiella spp., and Francisella spp. was determined as the highest dilution of genomic DNA that still tested as positive. 103 genome copies exhibited 10% of the fluorescence intensity of the M probe, while 102 genome copies produced no detectible signal; the LOD was therefore determined to be 103 copies and 10% of the positive control. All capture probes are listed in Table 1. The fluorescence intensity of the capture probes is expressed as a percentage of the fluorescence intensity of the M probe.