Ratiometric Fluorescence Sensing of Arsenate(V) and Phosphate Ions Using an Inclusion Complex of Modified γ-Cyclodextrin with a Simple Zinc(II)–Dipicolylamine-Type Probe

Group 15 anions such as monophosphate ions (Pi) and arsenate(V) ions (As(V)) have a tremendous impact on the environment and living organisms, and simple methods to detect these anions have been desired. We designed a supramolecular complex, Zn–C6O/FBγCyD, consisting of a simple zinc(II)-dipicolylamine-type fluorescent probe (Zn–C6O) and fluorophenylboronic acid-modified γ-cyclodextrin (FBγCyD), for the fluorescence sensing of Pi and As(V). Upon binding to Pi, Zn–C6O/FBγCyD displayed a change in fluorescence color owing to the pyrene moieties of Zn–C6O forming a dimer in the FBγCyD cavity, allowing for the selective detection of Pi in a ratiometric manner among various phosphate derivatives. The dimer formation was confirmed by the appearance of pronounced bisignate Cotton effects in the induced circular dichroism (ICD) spectra. Zn–C6O/FBγCyD also exhibited a similar ratiometric response to As(V) with a linear fluorescence response in the range of As(V) concentrations of 5–30 μM, suggesting that As(V) can be quantified in this concentration range. For application to real samples, spike tests were conducted in well waters. The results showed linear relationships between the fluorescence intensity ratio and As(V) concentration, demonstrating that the As(V) detection of Zn–C6O/FBγCyD is possible even in the presence of foreign substances. This study presents the high availability of the cyclodextrin-based supramolecular chemosensor for the design of fluorescent probes detecting oxyanions, which brings high water solubility, structural simplicity, and unusual selectivity that are hardly realized by conventional chemosensors.