Assembly of myoglobin layer-by-layer films with poly(propyleneimine) dendrimer-stabilized gold nanoparticles and its application in electrochemical biosensing

The small-sized Au nanoparticles (3 nm) were prepared by reduction of HAuCl4 in the presence of poly(propyleneimine) (PPI) dendrimers, forming the stable PPI–Au nanoclusters in aqueous medium. The PPI–Au nanoclusters might take a kind of “core–shell” structure, in which several PPI molecules were attached on the surface of one gold nanoparticle. The PPI–Au nanoclusters in aqueous dispersions and myoglobin (Mb) in its buffers at pH 5.0 were then alternately adsorbed on the surface of pyrolytic graphite (PG) electrodes and other solid substrates, forming {PPI–Au/Mb}n layer-by-layer films, which was confirmed by cyclic voltammetry (CV) and quartz crystal microbalance (QCM). {PPI–Au/Mb}n films on PG electrodes demonstrated a pair of well-defined and quasi-reversible CV reduction-oxidation peaks for Mb heme FeIII/FeII couple and good electrocatalytic properties toward reduction of oxygen and hydrogen peroxide. Compared with {Au/Mb}n multilayer films containing no dendrimers and {PAMAM/Mb}n films assembled by polyamidoamine (PAMAM) dendrimers and Mb but in the absence of Au nanoparticles, {PPI–Au/Mb}n films showed better electrochemical behaviors and catalytic performances, which may be attributed to the unique structure of PPI–Au nanoclusters and good conductivity of gold nanoparticles. This novel kind of protein multilayer films assembled with dendrimer-stabilized gold nanoparticles may provide a new and general approach to fabricate the biosensors and bioreactors based on the direct electrochemistry of proteins or enzymes.