Metal ion-induced dual fluorescent change for aza-crown ether acridinedione-functionalized gold nanorods and quantum dots

Abstract

Aza-crown ether acridinedione-functionalized quantum dots (ACEADD-QDs) and aza-crown ether acridinedione-functionalized gold nanorods (ACEADD-GNRs) have been developed as a pair for a fluorescent chemosensor detecting metal ions. The ACEADD-QDs have dual emissions at a visible wavelength of ∼430 nm from the acridinedione dye moiety and at a near-infrared (NIR) wavelength of ∼775 nm from the CdTeSe QDs. In the presence of Ca²⁺ or Mg²⁺ ions, the ACEADD-QD and ACEADD-GNR pair can form a sandwich complex mediated by the metal ion. The ACEADD-QD and ACEADD-GNR complex pair shows visible fluorescence enhancement from the acridinedione dye and concurrent fluorescence quenching from the NIR QD. The aza-crown ether complex results in the suppression of photoinduced electron transfer from the aza-crown ether to the acridinedione dye moiety. At the same time, the QD fluorescence can be effectively quenched by the nanometal surface energy transfer from the QD to the GNR. This ACEADD-QD and ACEADD-GNR pair can effectively transduce the selective binding event of crown ethers with metal ions into the simultaneous modulation of the enhancement in dye fluorescence and the quenching of QD emission, which can open a new strategy for ratiometric sensors that are selective and robust against the environment conditions.