Fluorescent hydrogel of chitosan and gelatin cross-linked with maleic acid for optical detection of heavy metals

A multi-component, fluorescent hydrogel of chitosan and gelatin using maleic acid as a cross-linking agent was fabricated with improved mechanical and thermal properties. The FTIR spectroscopy and SEM studies confirmed the formation of a cross-linked and porous hydrogel. The XPS studies confirmed the presence of rich functionalities over the surface of hydrogel. The hybrid hydrogel possessed strong blue emission band centered at 438 nm when excited with an absorption band centered at 384 nm. The fluorescent hydrogel was tested for selective detection of different heavy metal ions including Cr (VI) in the aqueous solution. The strong complexation among the functional groups of hydrogel and metal ions led to the quenching of hydrogel's fluorescence. The fluorescence of hydrogel was quenched significantly in the presence of Cr (VI) ions in comparison to the other heavy metal ions. The fluorescence-quenching efficiency displayed a linear response to the Cr (VI) concentration in the range of 1-14 nM with a lower detection limit of 0.12 nM. Embraced with good sensitivity and selectivity for Cr (VI) ions, the solid hydrogel with stable fluorescent properties holds a great potential in chemical sensing applications.