The review covers recent developments in which quantum dots (QDs) are combined with electrodes for detection of analytes. Special focus will be on the generation of photocurrents and the possibility of spatially resolved, light-directed analysis. Different modes for combining biochemical reactions with QDs will be discussed. Other applications involve the use of QDs as labels in binding analysis. Different methods have been developed for read-out. In addition to photocurrent analysis, voltammetric detection of metals and electrochemiluminescence (ECL) can be used. In the latter, light is the sensor signal. ECL-based systems combine the advantage of very sensitive analytical detection with rather simple instrumentation.
A supramolecular multicomponent protein architecture on electrodes is developed that allows the establishment of bidirectional electron transfer cascades based on interprotein electron exchange. The architecture is formed by embedding two different enzymes (laccase and cellobiose dehydrogenase) and a redox protein (cytochrome c) by means of carboxy-modified silica nanoparticles in a multiple layer format. The construct is designed as a switchable dual analyte detection device allowing the measurement of lactose and oxygen, respectively. As the switching force we apply the electrode potential, which ensures control of the redox state of cytochrome c. The two signal chains are operating in a non-separated matrix and are not disturbed by the other biocatalyst.
Keywords:Copper / N ligands / Pi interactions / Self-assembly / Immobilization 2,11-Dialkylated 1,12-diazaperylenes (alkyl = Me, Et, iPr) dmedap, detdap and dipdap have been synthesized by reductive cyclization of 3,3Ј-dialkylated 1,1Ј-biisoquinolines 3a-c, resulting in the first copper(I) complexes of a "largesurface" ligand.
The redox behavior
of proteins plays a crucial part in the design
of bioelectronic systems. We have demonstrated several functional
systems exploiting the electron exchange properties of the redox protein
cytochrome c (cyt c) in combination
with enzymes and photoactive proteins. The operation is based on an
effective reaction at modified electrodes but also to a large extent
on the capability of self-exchange between cyt c molecules
in a surface-fixed state. In this context, different variants of human
cyt c have been examined here with respect to an
altered heterogeneous electron transfer (ET) rate in a monolayer on
electrodes as well as an enhanced self-exchange rate while being incorporated
in multilayer architectures. For this purpose, mutants of the wild-type
(WT) protein have been prepared to change the chemical nature of the
surface contact area near the heme edge. The structural integrity
of the variants has been verified by NMR and UV–vis measurements.
It is shown that the single-point mutations can significantly influence
the heterogeneous ET rate at thiol-modified gold electrodes and that
electroactive protein/silica nanoparticle multilayers can be constructed
with all forms of human cyt c prepared. The kinetic
behavior of electron exchange for the mutant proteins in comparison
with that of the WT has been found altered in some multilayer arrangements.
Higher self-exchange rates have been found for K79A. The results demonstrate
that the position of the introduced change in the charge situation
of cyt c has a profound influence on the exchange
behavior. In addition, the behavior of the cyt c variants
in assembled multilayers is found to be rather similar to the situation
of cyt c self-exchange in solution verified by NMR.
Fully electroactive multilayer architectures combining the redox protein cytochrome c and the enzyme laccase by the use of silica nanoparticles as artificial matrix have been constructed on gold electrodes capable of direct dioxygen reduction. Laccase form Trametes versicolor and cytochrome c from horse heart were electrostatically coimmobilized by alternate deposition with interlayers of silica nanoparticles in a multilayer fashion. The layer formation has been monitored by quartz crystal microbalance. The electrochemical properties and performance of the nanobiomolecular entities were investigated by cyclic voltammetry, indicating, that a multistep electron transfer cascade, from the electrode via cytochrome c in the layered system toward the enzyme laccase, and here to molecular dioxygen was achieved. The response of the novel architecture is based on direct electron exchange between immobilized proteins and can be tuned by the assembly process.
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