Abstract A simple and selective colorimetric sensor based on o-phosphorylethanolamine-functionalized gold nanoparticles (OPA–Au NPs) as an optical probe has been developed for the detection of UO22+. OPA–Au NPs rapidly aggregate in the presence of UO22+, thereby causing a visual color change from red to blue, which is easily detectable by eye. The proposed sensing system possesses a selective response for UO22+ over other heavy metal ions. The current method shows application potential for UO22+ detection in real water samples.