A pentaerythritol-based metallodendrimer with
ruthenium(II) terpyridine units, Ru
IIDen, catalyzed the oxidation of
L-methionine and insulin at pH 7.0. The Ru
IIDenwas immobilized on a carbon surface through layer-by-layer electrostatic deposition; the negatively chargedpolymer, poly(styrene sulfonate), was its counterpart.These bilayers were assembled on a glassy carbon electrode that was first modified by deposition of a layer ofthe conjugate base of sulfanilic acid and then with quaternized poly(4-vinylpyridine). Reversible voltammetry forthe Ru
II/III redox couple was observed, the current forwhich increased linearly with layer number,
n, of Ru
IIDen up to
n = 12. Cyclic voltammetry was used todemonstrate the mediation of
L-methionine oxidation bya Ru
IIDen-containing multilayer assembly. Flow injectionamperometric determination of insulin at pH 7.0 at thismodified electrode yielded a calibration curve with thefollowing characteristics: linear dynamic range, 6 nM-0.4
M; sensitivity, 225 nA
M
-1; detection limit (
k = 3c
riterion), 2 nM. Of particular importance was that thesensitivity was proportional to the number of Ru
IIDenlayers.
