Aggregation-Induced Emission of 1,8-Naphthalimide-Casein Micelle: Investigation by Synchronous Spectrographic Method

A novel 1,8-naphthalimide probe 1, bearing two acetic-acid moieties was synthesized. The acetic-acid groups, docked into the sub-domains of casein micelle and bound with tryptophan residues, and the 1,8-naphthalimide chromophore adsorbed on the surface of casein micelle, forming a supermolecule, 1casein micelle, which exhibited the aggregation-induced synchronous emission (AISE) characters. The effect of pH on the intensity of supermolecule was investigated, and the result indicated that the emission enhancement was mainly due to the 1,8-naphthalimide chromophore aggregated onto the casein micelle. Based on AISE, a novel casein quantification method was developed, which exhibited a good linear range of 0.05-10.0g ml(-1) and 0.07-9.5g ml(-1) with the detection limits of 2.8 and 3.0ng ml(-1). The effects of metal ions and pH on the system of 1casein micelle were investigated. The proposed method was applied to determine casein in milk samples, and the results were in good agreement with the result of the Biuret method.