Cysteine functionalized naphthalene diimide unit for mercury ion sensing

A naphthalene diimide-based fluorescent sensor was synthesized for the detection of mercury ions. The sensor incorporates cysteine, a biological molecule containing a thiol functional group, as the active component within the naphthalene dianhydride unit. This thiol group exhibited a pronounced affinity for mercury ions, which was monitored through fluorescence experiments. Upon the introduction of mercury ions, it was observed a substantial ~78% reduction in the fluorescence activity. The Limit of Detection (LOD) or sensitivity for the NDI-Cys sensor was determined to be 0.11 ppm, with a measurement range spanning from 0.11 ppm to 1.13 ppm.