In the design of dual-imaging probes, the first functionalized and neutral heterobimetallic Re(I)-Gd(III) complex, highly soluble in aqueous solutions, has been prepared. This system exhibits interesting photo-physical properties (lambda(em) = 578 nm, = phi = 1.4%) for optical imaging and substantial higher relaxivity (r(1) - = 6.6 mM(-1) s(-1) at 0.47 T and 37 degrees C) than the clinically used MRI contrast agents. Moreover, this system incorporates an aromatic ester functionality suitable for bioconjugation. (c) 2013 Elsevier Ltd. All rights reserved.