A novel molecular probe sensing polynuclear hydrolyzed aluminum by chelation-enhanced fluorescence

A novel molecular probe (P2) sensing polynuclear hydrolyzed aluminum by chelation-enhanced fluorescence was described, which was prepared from 1,1ʹ-(1,4-phenylene)bis(7-methyl-1,3,5-octanetrione) and 2-aminomethylpyridine. P2 showed a strong fluorescence response to Al(III) when excited by the optimized wavelength of 400 nm and the λmax,em at 505 nm indicated a hypsochromic shift of 11 nm to that of free P2, but Cu(II) was observed to quench the fluorescence intensity to nearly zero. The P2–Al(III) complex indicated the best fluorescence response at a pH near 7 and there might be a relevance to the amphoteric property of the aluminum hydroxide. The emission intensity at 505 nm continued to increase until the mole ratio of [Al(III)]/[P2] reached a value of 13 and no stoichiometry was observed during the process, which implied that the sensing target of the P2 probe was not the free aluminum ion but the polynuclear hydrolyzed aluminum. The binuclear hydrolyzed aluminum compounds were selected as model target molecules to simulate the energy-minimized structure of the P2–Al(III) complex to confirm the CHEF mechanism. The enhanced fluorescent images of HeLa cells incubated with 1 μM P2 and 5 μM Al(III) were obtained.