We developed a new o-phenylenediamine-based compound as a turn-on fluorescent probe for nitric oxide (NO) with a large blue shift in absorption. It showed high selectivity and sensitivity toward nitric oxide over other ROS and RNS species in neutral buffer solution. The analytical detection limit (ADL) was 30 nM. As far as we are aware this is the first o-phenylenediamine-based NO probe using Cu²⁺ as a promoter.