Dual on–off and off–on switchable oligoaziridine biosensor

A water-soluble biocompatible aziridine-based biosensor with pendant anthracene units was synthesized by radicalar polymerization of N-substituted aziridines in supercritical carbon dioxide. The binding ability of the sensor towards a series of metal ions was examined by comparing the fluorescence intensities of the solutions before and after the addition of 100 equivalents of a solution of the metal ion chloride salt. A fast, simple and highly optical sensitive dual behavior, “off–on” and “on–off” response, was observed after the biosensor was exposed to the metal cations in aqueous solution. Zinc presented the highest fluorescence enhancement (turn-on) and copper presented the highest fluorescence quenching (turn-off). The response time was found to be instantaneous and the detection limit was achieved even in the presence of excess metal cation competitors. By using immunofluorescence microscopy it was also shown that oligoaziridine acts as an “on–off” probe through highly sensitive (detection limit of 1.6nM), selective and reversible binding to copper anions under physiologic conditions using living Human Fibroblast cells. The stoichiometry for the reaction of the biosensor with Cu2+ was determined by a Job plot and indicates the formation of an oligoaziridine-Cu2+ 1:2 adduct. [Display omitted] ► A water-soluble biocompatible aziridine-based biosensor was synthesized in scCO2. ► The biosensor presents a dual behavior when exposed to different metal cations. ► Zinc displays the highest fluorescence enhancement (turn-on). ► Cu2+ shows the highest fluorescence quenching (turn-off) with detection limit of 1.6nM. ► The biosensor is able to detect traces of Cu2+ within living Human Fibroblast cells.