A fluorescent chemosensor, ortho-methylated boron-dipyrromethene (o-MBDP) has been synthesized and characterized. It featured excellent selectivity and sensitivity for Ag+ and Hg2+ ions, which could enhance the weak fluorescence of o-MBDP drastically by several hundred times through coordination and as a result, behave as an efficient "turn-on" fluorescent probe. The detection upper limit for Ag+ ion could be decreased by at least one order of magnitude with the introduction of the ortho-methyl group, in comparison with analogous boron-dipyrromethene (BDP) sensors, indicating the feasibility in extensive application areas as chemosensors. (c) 2013 Elsevier B.V. All rights reserved.