METAL-ION TRACE DETECTION BY A CHELATOR-MODIFIED GOLD ELECTRODE - A COMPARISON OF SURFACE TO BULK AFFINITY

The binding of metal ions to self-assembled nitrilotriacetic acid (NTA )-modified thioalkane monolayers was monitored by impedance spectrosco py via a capacitance change of the blocking gold electrode. Binding to a fluorescent NTA-derivative and the native NTA, measured in bulk by fluorescence quenching and isothermal titration calorimetry, was deter mined for comparison. Surface and bulk absolute dissociation constants K-abs of metal ion-NTA complexes for these three derivatives showed n o significant differences. Cu2+ concentrations as low as 0.5 nM (30 pp t) could be detected by impedance spectroscopy. This concept of metal ion trace detection might be further extended to other chelating group s for use in future applications.