Nanomaterial surface energy transfer (NSET) has been powerful since it is capable of measuring the energy transfer from a donor molecule to a nanoparticle surface with the distance nearly twice as far as fluoresence resonance energy transfer (FRET).In this contribution, a simple and rapid spectrofluorometric method of captopril was developed based on its obstruction effect on the NSET from acridine orange (AO) to gold nanoparticles (Au NPs).