A charger adapted to uniformly charge a surface of an image bearing member is provided. The apparatus includes a running power controlling and recording unit and an interval adjusting unit which adjusts an interval for performing running power control and makes a suitable ROPC operation possible even if conditions for recording information are changed. In some embodiments using sandwich assay methodology, the capture probes hybridize complementary target nucleic acid sequences, which in turn are bound to detection probes comprising nanoparticle-oligonucleotide conjugates comprising target-complementary oligonucleotides.