Electrochemical oxidation of polyamines at diamond thin-film electrodes

The oxidation of five polyamines (ethylenediamine, putrescine, cadaverine, spermine, and spermidine) was investigated at polycrystalline, boron-doped, diamond thin-film electrodes using cyclic voltammetry and flow injection a nalysis (FIA) with amperometric detection. Cyclic voltammetry of the polyam ines was conducted in pH 10 carbonate buffer. Well-resolved oxidation waves with respect to the background signal were observed, and the current-poten tial curves exhibited a scan rate dependence characteristic of slow desorpt ion kinetics of the polyamine oxidation product. E-1/2's of similar to+ 0.8 8 V vs Ag/AgCl were measured for all five polyamines. A mechanism is propos ed whereby the polyamine oxidation occurs by oxygen transfer from reactive OH radicals. These radicals are produced during the initial stage of oxygen evolution at the nondiamond carbon impurity sites. These sites are believe d to be located primarily at the grain boundaries, isolated from one anothe r by the diamond microcrystallites, although the impurities could also exis t as extended defects within the lattice. Stabilization of the polyamine pr ior to oxidation is achieved through adsorption/complexation of the amine f unctionality with surface boron dopant atoms, also clustered at the grain b oundaries. In general, the FIA results demonstrated that the diamond can be used to effectively detect all five polyamines with a concentration limit of quantitation of similar to 1 mu M (S/N greater than or equal to 3) and a linear dynamic range from 10(-3) to 10(-6) M (r(2) > 0.97), These detector figures of merit were achieved at constant potential without prior derivat ization. Lower quality rather than higher quality diamond films are needed for this assay, and the requisite film properties can be introduced by judi cious choice of the deposition conditions.