Reusable polymer film chemosensor for ratiometric fluorescence sensing in aqueous media

A novel strategy for building a polymeric film sensor was reported. First, a florescence resonance energy transfer (FRET)-based dyad was synthesized as the sensing probe, of which a spirolactam-rhodamine derivative (SRhB) was utilized as the ion-recognition element for Fe3+ ions, and a ring-opening reaction of SRhB induced by Fe3+ generates the long-wavelength rhodamine B fluorophore which can act as the energy acceptor; and dansyl moiety was chosen as the donor, whose emission spectrum overlaps with the absorption spectrum of the open-ring state of SRhB. The fluorescent dyad was then covalently linked into the PVA matrix, forming a ratiometric fluorescent sensing film usable in aqueous media for Fe3+ ions. This reusable and free-standing film can be utilized conveniently to achieve real-time sensing in aqueous medium just like using a test paper. For this approach, the recognition fluorophores reside not only on the film surface, but throughout the whole film, and the PVA-based film can swell and form into the hydrogel in water, thus allowing for wider detection range as well as obvious visual observation. This film may be used in environment applications as well as in food industry due to the low-toxic and biocompatible polymer film.