Fluorescent magnetic nanosensors for Zn2+ and CN− in aqueous solution prepared from adamantane-modified fluorescein and β-cyclodextrin-modified Fe3O4@SiO2via host–guest interactions

Abstract

A novel multifunctional fluorescent chemosensor has been constructed with a highly selective “off–on” behavior, recoverability and recyclability based on β-CD/AD (adamantane) host–guest self-assembly interactions. Adamantane-modified fluorescein/cyclodextrin-modified Fe₃O₄@SiO₂ inclusion complex magnetic nanoparticles (FFIC MNPs), which can provide a specific green fluorescence enhancement in response to Zn²⁺, have a detection limit of 4.5 × 10⁻⁷ mol L⁻¹ in CH₃CN : H₂O (1 : 4, v/v). The spirolactam ring in the fluorophore moiety would be open with the introduction of Zn²⁺, while it could recover as long as the zinc in the complex is removed. Meanwhile, one gram of FFIC MNPs can adsorb 6.1 mg zinc. Therefore, the derivative chemosensors, FFIC MNPs–Zn, are available to respond to CN⁻ due to the fluorescence quenching under UV (ultraviolet) radiation with a detection limit of 7.7 × 10⁻⁷ mol L⁻¹. Furthermore, the FFIC MNPs exhibit great reusability and recyclability in aqueous solution on account of their magnetism and reproducibility. We recycle the residual MNPs to detect Zn²⁺ repeatedly for at least 4 times, after readily adsorbing the complex zinc with excess CN⁻, and the same principle also works in reverse. If the fluorophore moiety is inactive, we could also wash out the useless fluorescent molecules from the MNPs (hosts) and then reassemble new fluorescent small-molecules (guests) to maintain the efficient properties of the probe in responding to Zn²⁺ and CN⁻ for at least 7 times.