A bis(fluorenyl-triazole)-conjugated naphthoquinoline-dione probe for a cascade detection of Cu2+ and F− and its logic circuit with a memory unit

Abstract

Wide usage of Cu2+ and F− in various industries and their potential hazard toward human health necessitate the development of a probe for their selective and sensitive detection. While various probes have been invented for the respective detection of these two ions, there are few probes allowing for their simultaneous or sequential detection. The current study introduces a naphthoquinoline-dione probe (probe 1) that contains two fluorenyl-triazole units conjugated to the probe aromatic core via an amine functional group. Fluorescence emission of the probe was selectively quenched upon addition of Cu2+ among various metal ions, and the resulting [probe 1-Cu2+] complex displayed ‘Turn-On’ fluorescence upon addition of F−. Over the course of this cascade detection, the calculated LODs of the probe were 0.046 (Cu2+) and 0.10 pM (F−). The effective fluorescence quenching and restoration (i.e., cascade detection) observed were enabled by the strong binding of Cu2+ to the probe and a subsequent dissociation of this metal ion from the probe due to the presence of F−, respectively. The ‘ON and OFF’ luminescence observed in the solution state of the probe was reproduced when probe 1, which was absorbed on solid supports, was used for detection. These results were replicable when the solid-supported probe 1 was used to sense Cu2+ or F− from various real samples such as urine (Cu2+) and dental care solution (F−). Based on these results, we built an “ON-OFF-ON” molecular switch and fabricate a molecular logic circuit with a memory unit.