A molecular two-photon sensor for the metal ions derived from bis(2-pyridyl)amine as the receptor is reported. The sensor emits strong two-photon fluorescence when excited by 780 nm laser photons. Moreover, the binding constants measured by the one- and two-photon fluorescence are similar. This result may be useful for the design of efficient two-photon fluorescence probe for biological substrates. (c) 2005 Elsevier B.V. All rights reserved.