Enhanced Turn-On Fluorescence Detection of Aqueous Lead Ions with Size-Shrinkable Hydrogels

[Image: see text] Highly sensitive detection of lead ions in water is of importance. This paper reports a new method to enhance the sensitivity of fluorescence detection of aqueous lead ions by exploiting the large volume reduction of hydrogels upon dehydration. Rhodamine-derived prefluorescent probes with high selectivity to lead ions are grafted on a carboxylated agarose hydrogel. Upon binding low-concentration lead ions, fluorescence emission is turned on. The dehydration of the hydrogel leads to a size reduction of over 40 times and an enhancement of fluorescence of 10 times at a lead-ion concentration of 10(–7) M, allowing fluorescence detection with naked eyes. Given its low cost, easy operation, and high sensitivity, the volume reduction hydrogel can be used to detect lead ions in drinking water.