Colorimetric Detection of Spermine by the CuII Complex of Imine-Based Organic Nanoaggregates in Aqueous Medium

A Schiff-base receptor bearing different functionalities was synthesized from dipicolinic acid hydrazide and characterized with several spectroscopic techniques. To explore its practical application as a sensor, the receptor was processed into organic nanoaggregates (O1) in aqueous medium by the reprecipitation method. The O1 nanoaggregates were characterized by techniques such as dynamic light scattering and TEM, and their recognition properties for metal ions were investigated by fluorescence spectroscopy. The nanoaggregates showed selectivity for Cu2+ over other metal ions. The structure of the complex O1Cu(2+) thus formed was determined by single-crystal X-ray crystallography. Complex O1Cu(2+) was further employed as a sensor for detection of biogenic amines in aqueous medium, and showed selective sensing of spermine with a detection limit of 7.62 nM. The color change on addition of spermine to the complex can be seen with the naked eye. Moreover, stability in the physiological pH range and negligible effect of ionic environment provided the opportunity for real-time application of the sensor in aqueous medium.