CdSe/ZnS quantum clots (QD) have been surface functionalised with mercaptoaniline and N-(o-methoxyphenyl)aza-15-crown-5 receptors, the former serving as a receptor for protons with the latter serving as a receptor for sodium ions. In conditions of low protons and sodium ions the QD fluorescence Was quenched by a photoinduced electron transfer (PET) process from the receptors to the excited QD. The simultaneous addition of both protons and sodium ions, however, restored the QD emission while the independent addition of either ion had no effect. Thus, the conditions of a two input AND molecular logic gate were satified with protons and sodium ions as inputs and 560 nm QD fluorescence as Output. (C) 2009 Elsevier B.V. All rights reserved.