A novel multifunctional colorimetric sensor HMBC ((E)â3â((2âhydroxyâ3âmethoxybenzylidene)amino)benzofuranâ2âcarboxamide), based on 3âaminobenzofuranâ2âcarboxamide and 2âhydroxylâ3âmethoxylbenzaldehyde, was designed and synthesized. The chemosensor HMBC could sense Co2+, Cu2+, and Zn2+ by color changes from colorless to yellow. Limits of detection (0.38, 0.41, and 1.02 ÎŒM) of HMBC for Co2+, Cu2+, and Zn2+ were much lower than the New Jersey Department of Environmental Protection (NJDEP) standard (1.70 ÎŒM) for Co2+ and the WHO guidelines (31.5 ÎŒM and 76 ÎŒM) for Cu2+ and Zn2+. Significantly, HMBC could be applied for the quantification of Co2+, Cu2+, and Zn2+ in real samples. The sensing process of HMBC for Co2+, Cu2+, and Zn2+ was well demonstrated by 1H NMR and UVâVisible titrations, Job plots, theoretical calculations, and ESIâmass spectroscopy.