A redox polymer, poly(ethylenimine)ferrocene (PEI-Fc) was prepared by attaching electroactive ferrocene groups to the
backbone of a water soluble, biocompatible polyelectrolyte, poly(ethylenimine), and multilayer film composed of
polystyrenesulfonate sodium (PSS) and PEI-Fc was prepared by alternate layer-by-layer (LBL) self-assembly adsorption
technique based on the electrostatic force between the opposite charges carried by these two polymers. UV-Vis spectra
was used to monitor the LBL process, and the thickness and immobilization amount of each layer were characterized by
quartz crystal microbalance (QCM), which showed the formation of nano-scale multilayer structure and linear mass
increase dependent on the alternate adsorption cycles. The electrochemical properties of the PEI-Fc/PSS multilayer film
modified gold electrode were investigated by cyclic voltammetry. It was observed clearly that the electrochemical
properties of this multilayer film were strongly dependent on the layer number and the ferrocene content in PEI-Fc. The
electrochemical kinetic was analyzed based on a general model for surface process, and the experimental data fitted well
with that evaluated from the above model. This redox polymer showed potential for the construction of reagentless
biosensor.
As coenzyme utilized by more than hundreds of dehydrogenases, the efficient immobilization and regeneration of
nicotinamide adenine dinucleotide (NAD+) are of great importance and have practical applications in industrial,
analytical and biomedical field. In this paper, an electroactive macromolecular weight coenzyme derivative (PEI-DHBNAD)
was prepared by attaching both NAD+ and 3,4-dihydroxybenzaldehyde (3,4-DHB) to a water-soluble
polyelectrolyte, poly(ethylenimine) (PEI). The functional polymer exhibited both electrochemical properties of catechol
unites and coenzymatic activity of NAD moieties. The macromolecular NAD analogue showed a substantial degree of
efficiency relative to free NAD+ with alcohol dehydrogenase (ADH) and glucose-6-phophate dehydrogenase (G6PDH),
and a litter higher Michaelis-Menton constant (Km) was obtained for the coenzyme derivative than free NAD+. The
bioelectrochemical properties of PEI-DHB-NAD were investigated by using G6PDH as the model enzyme, and both of
them were retained on electrode surface by ultrafiltration membrane. The modified electrode showed typical response to
substrate without the addition of free coenzyme, which indicated that PEI-DHB-NAD can carry out the electron transfer
between electrode and NAD-dependent dehydrogenase. The utilization of polymer-based PEI-DHB-NAD is convenient
for the immobilization of both electron mediator and coenzyme, and offers a practical approach for the construction of
reagentless biosensors.
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