8-Oxoguanosine (8-oxoG) is derived from the oxidation of guanosine (dG) and is known to induce transversion mutations (G:C to T:A) in DNA. We have already reported the fluorescent probe "8-oxoG-clamp", which shows a selective fluorescence quenching phenomenon toward 8-oxoG. In this study, attachment of an additional fluorophore to 8-oxoG-clamp was investigated as a strategy for the detection of 8-oxoG by a fluorescence color change attributed to the 8-oxoG-clamp.