4 research outputs found
Enzyme-Catalyzed O<sub>2</sub> Removal System for Electrochemical Analysis under Ambient Air: Application in an Amperometric Nitrate Biosensor
Electroanalytical procedures are often subjected to oxygen
interferences. However, achieving anaerobic conditions in field analytical
chemistry is difficult. In this work, novel enzymatic systems were
designed to maintain oxygen-free solutions in open, small volume electrochemical
cells and implemented under field conditions. The oxygen removal system
consists of an oxidase enzyme, an oxidase-specific substrate, and
catalase for dismutation of hydrogen peroxide generated in the enzyme
catalyzed oxygen removal reaction. Using cyclic voltammetry, three
oxidase enzyme/substrate combinations with catalase were analyzed:
glucose oxidase with glucose, galactose oxidase with galactose, and
pyranose 2-oxidase with glucose. Each system completely removed oxygen
for 1 h or more in unstirred open vessels. Reagents, catalysts, reaction
intermediates, and products involved in the oxygen reduction reaction
were not detected electrochemically. To evaluate the oxygen removal
systems in a field sensing device, a model nitrate biosensor based
on recombinant eukaryotic nitrate reductase was implemented in commercial
screen-printed electrochemical cells with 200 Ī¼L volumes. The
products of the aldohexose oxidation catalyzed by glucose oxidase
and galactose oxidase deactivate nitrate reductase and must be quenched
for biosensor applications. For general application, the optimum catalyst
is pyranose 2-oxidase since the oxidation product does not interfere
with the biorecognition element
Surface-Attached Poly(glycidyl methacrylate) as a Versatile Platform for Creating Dual-Functional Polymer Brushes
Novel
types of dual-functional surface-attached polymer brushes
were developed by post-polymerization modification of polyĀ(glycidyl
methacrylate) brushes on glassy carbon substrates. Azide and alcohol
groups were initially introduced by epoxide ring-openings of the side
chains. These polymer brushes represent an attractive chemical platform
to deliberately introduce other molecular units at specific sites.
In this work, ferrocene and nitrobenzene redox units were immobilized
through the two groups to create redox polymers. In-depth analysis
by infrared reflectionāabsorption spectroscopy and X-ray photoelectron
spectroscopy revealed an almost quantitative conversion of the modification
reactions. The electrochemical activity of the ferrocenyl part of
this diode-like system was fully expressed with an electron transfer
rate constant = 1.2 s<sup>ā1</sup> and surface density = 0.19
nmol cm<sup>ā2</sup> per nm section of the film, independent
of its thickness. In contrast, for the nitrobenzene moieties diffusion
of counterions (i.e., tetraalkylammonium) easily becomes the rate-controlling
step, thereby leaving a substantial fraction of them electrochemically
inactive
Protection and Reactivation of the [NiFeSe] Hydrogenase from <i>Desulfovibrio vulgaris</i> Hildenborough under Oxidative Conditions
We
report on the fabrication of bioanodes for H<sub>2</sub> oxidation
based on [NiFeSe] hydrogenase. The enzyme was electrically wired by
means of a specifically designed low-potential viologen-modified polymer,
which delivers benchmark H<sub>2</sub> oxidizing currents even under
deactivating conditions owing to efficient protection against O<sub>2</sub> combined with a viologen-induced reactivation of the O<sub>2</sub> inhibited enzyme. Moreover, the viologen-modified polymer
allows for electrochemical co-deposition of polymer and biocatalyst
and, by this, for control of the film thickness. Protection and reactivation
of the enzyme was demonstrated in thick and thin reaction layers
High-Density Droplet Microarray of Individually Addressable Electrochemical Cells
Microarray technology
has shown great potential for various types
of high-throughput screening applications. The main read-out methods
of most microarray platforms, however, are based on optical techniques,
limiting the scope of potential applications of such powerful screening
technology. Electrochemical methods possess numerous complementary
advantages over optical detection methods, including its label-free
nature, capability of quantitative monitoring of various reporter
molecules, and the ability to not only detect but also address compositions
of individual compartments. However, application of electrochemical
methods for the purpose of high-throughput screening remains very
limited. In this work, we develop a high-density individually addressable
electrochemical droplet microarray (eDMA). The eDMA allows for the
detection of redox-active reporter molecules irrespective of their
electrochemical reversibility in individual nanoliter-sized droplets.
Orthogonal band microelectrodes are arranged to form at their intersections
an array of three-electrode systems for precise control of the applied
potential, which enables direct read-out of the current related to
analyte detection. The band microelectrode array is covered with a
layer of permeable porous polymethacrylate functionalized with a highly
hydrophobicāhydrophilic pattern, forming spatially separated
nanoliter-sized droplets on top of each electrochemical cell. Electrochemical
characterization of single droplets demonstrates that the underlying
electrode system is accessible to redox-active molecules through the
hydrophilic polymeric pattern and that the nonwettable hydrophobic
boundaries can spatially separate neighboring cells effectively. The
eDMA technology opens the possibility to combine the high-throughput
biochemical or living cell screenings using the droplet microarray
platform with the sequential electrochemical read-out of individual
droplets