A reversible turn-on sensor (Rh-OH-Rh) which can selectively detect Fe3+ in solution has been developed. The sensor combines two rhodamine moieties with a 3-oxygen Fe3+ receptor to provide excellent selectivity for Fe3+ over a range of biologically relevant metal ions. It binds Fe3+ in a 1:1 stoichiometry with an apparent binding constant 5.2 x 10(6) M-1 (log K = 5.28) in ACN/DMF (9/1 v/v) solution. The sensor displays distinct "on-off" changes in color and fluorescence upon the alteration of free Fe3+ levels in solution with a reversible response and little interference with other biological relevant metal ions. (C) 2012 Elsevier B.V. All rights reserved.