Visual recognition of melamine in milk via selective metallo-hydrogel formation

A series of novel six-coordinated terpyridine zinc complexes,containing ammonium salts and thymine fragment at the two terminals,have been designed and synthesized,which can function as highly sensitive visualized sensors for melamine detection via selective metallo-hydrogel formation.After fully characterization by various techniques,the complementary triple-hydrogen-bonding between the thymine fragment and melamine,as well as π-π stacking interactions may be responsible for the selective metallo-hydrogel formation.In light of the possible interference aroused by milk ingredients(proteins,peptides and amino acids) and legal/illegal additives(urine,sugars and vitamins),a series of control experiments are therefore involved.To our delight,this visual recognition is highly selective,no gelation was observed with the selected milk ingredients or additives.Remarkably,this new developed protocol enables convenient and highly selective visual recognition of melamine at a concentration as low as 10 ppm in raw milk without any tedious pretreatment.