A ratiometric fluorescent hydrogel sensor for zinc(II) based on a two fluorophore approach

A polymeric ratiometric fluorescent sensor for Zn(II) has been developed based on a Zn(II) responsive naphthalimide fluorophore (lambda(EM) 535 nm) and a Zn(II) insensitive rhodamine calibration fluorophore (lambda(EM) 579 nm) both coupled to a common poly(allyl amine) backbone. A concentration dependent increase in the ratiometric response (I-535 nm/I-579 nm) was observed in the 0-25 mM Zn(II) ion range for the sensor in aqueous buffer. The effect of dilution on the ratiometric intensity of the polymeric sensor was also studied and no change in ratiometric response was observed upon dilution to 50% of its original concentration. In contrast, when the polymeric sensor was incorporated within a Gantrez AN-139 hydrogel matrix, a linear ratiometric response was observed upon addition of increasing amounts of Zn(II) to the gel. Therefore, this approach offers the opportunity to determine Zn(II) concentration in environments where sensor concentration may vary dramatically.