Ultrasensitive electrochemical sensing of phosphate in water mediated by a dipicolylamine-zinc(II) complex

Dipicolylamine-zinc(II) complexes immobilized on gold electrodes allowed the selective electrochemical phosphate detection. The electrodes were prepared by assembling monolayers containing either (R)-N-(6-(bis(pyridine-2-ylmethyl)amino)hexyl)-5-(1,2-dithiolan-3-yl)pentanamide (DPA-hexyl) or (R)-N-(12-(bis(pyridine-2-ylmethyl)amino)dodecyl)-5-(1,2-dithiolan-3-yl)pentanamide (DPA-dodecyl) together with 4-mercapto-1-butanol (MB) on gold surfaces and subsequently adding zinc(II)nitrate to produce the corresponding surface-bound zinc (II) complexes. Both sensing systems displayed high sensitivity towards phosphate with detection limits close to 1.0 x 10(-15) M. Sensing was moreover very selective since sulfate, having a similar tetrahedral structure like phosphate, generated only a negligible electrochemical response. These electrodes were shown to allow the quantification of phosphate ions in lake water sample. Electrochemical studies indicated that the sensing mechanism was based on the redox activity of the pyridine units in the ligands complexed with Zn(II).