Cell-surface proteins, working as key agents in various diseases, are the targets for around 66% of approved human drugs. A general strategy to selectively detect these proteins in a real-time manner is expected to facilitate the development of new drugs and medical diagnoses. Although brilliant successes were attained using small-molecule probes, they could cover a narrow range of targets due to the lack of suitable ligands and some of them suffer from selectivity issues. We report herein an antibody-based fluorogenic probe prepared a two-step chemical modification under physiological conditions, to fulfill the selective recognition and wash-free imaging of membrane proteins, establishing a modular strategy with broad implications for biochemical research and for therapeutics.