Tuning of the selectivity of fluorescent peptidyl bioprobe using aggregation induced emission for heavy metal ions by buffering agents in 100% aqueous solutions

Smart fluorescent probes of which the detection of specific target molecules can be controlled are attracting remarkable interest. A fluorescent peptidyl bioprobe (1) was rationally synthesized by conjugating tetraphenylethylene, an aggregation-induced emission (AIE) fluorophore with a peptide receptor (AspHis) that acted as hard and intermediate bases. The selective detection of 1 for specific metal ion in 100% aqueous solutions was controlled by the buffering agents with the chelate effect without the change of pH. In distilled water and phosphate buffered aqueous solution at neutral pH, 1 exhibited a selective Off-On response to a soft metal ion, Hg2+ among test metal ions by 100-fold enhancement of the emission at 470 nm. 1 showed a selective Off-On response (180-fold enhancement) to a hard metal ion, Al3+ ions among test metal ions in Tris buffered aqueous solution at neutral pH and Hexamine (hexamethylenetetramine) buffered aqueous solution at acidic pH. The detection limit of 0.46 ppb for Hg2+ and 2.26 ppb for Al3+ in each condition was lower than the maximum allowable level of the metal ions in drinking water by EPA. This research helps to understand how buffering agents participate in the complex formation and aggregation of fluorescent probes using an AIE process for the selective detection of specific metal ions in aqueous solutions.