Gero Göbel

Development of a (PQQ)-GDH-anode based on MWCNT-modified gold and its application in a glucose/O2-biofuel cell

In this study a biofuel cell anode is developed on the basis of multi-walled carbon nanotubes (MWCNTs). Recombinant pyrroloquinoline quinone (PQQ) dependent glucose dehydrogenase (GDH) is covalently coupled to a PQQ-layer which is adsorbed onto thiol-modified MWCNTs at a gold electrode. In the presence of glucose a catalytic current starts at a potential of -80 mV vs. Ag/AgCl, 1M KCl. Under substrate saturation current densities of 170-200 μA/cm2 can be achieved. The operation is based on mediated electron transfer of the enzyme. This (PQQ)-GDH-MWCNT-electrode is combined with a MWCNT-modified electrode to which bilirubin oxidase (BOD) is covalently coupled. The resulting membrane-free biofuel cell has an open cell potential of 600 mV and can achieve a power density in the range of 23 μW/cm2.

Immobilization of Quantum Dots via Conjugated Self-Assembled Monolayers and Their Application as a Light-Controlled Sensor for the Detection of Hydrogen Peroxide

A light-addressable gold electrode modified with CdS and FePt or with CdS@FePt nanoparticles via an interfacial dithiol linker layer is presented. XPS measurements reveal that trans-stilbenedithiol provides high-quality self-assembled monolayers compared to benzenedithiol and biphenyldithiol, in case they are formed at elevated temperatures. The CdS nanoparticles in good electrical contact with the electrode allow for current generation under illumination and appropriate polarization. FePt nanoparticles serve as catalytic sites for the reduction of hydrogen peroxide to water. Advantageously, both properties can be combined by the use of hybrid nanoparticles fixed on the electrode by means of the optimized stilbenedithiol layer. This allows a light-controlled analysis of different hydrogen peroxide concentrations.

Light triggered detection of aminophenyl phosphate with a quantum dot based enzyme electrode

An electrochemical sensor for p-aminophenyl phosphate (p APP) is reported. It is based on the electrochemical conversion of 4-aminophenol (4AP) at a quantum dot (QD) modified electrode under illumination. Without illumination no electron transfer and thus no oxidation of 4AP can occur. p APP as substrate is converted by the enzyme alkaline phosphatase (ALP) to generate 4AP as a product. The QDs are coupled via 1,4-benzenedithiol (BDT) linkage to the surface of a gold electrode and thus allow potential-controlled photocurrent generation. The photocurrent is modified by the enzyme reaction providing access to the substrate detection. In order to develop a photobioelectrochemical sensor the enzyme is immobilized on top of the photo-switchable layer of the QDs. Immobilization of ALP is required for the potential possibility of spatially resolved measurements. Geometries with immobilized ALP are compared versus having the ALP in solution. Data indicate that functional immobilization with layer-by-layer assembly is possible. Enzymatic activity of ALP and thus the photocurrent can be described by Michaelis- Menten kinetics. p APP is detected as proof of principle investigation within the range of 25 μM - 1 mM.

Photoelectrochemical Sensor Based on Quantum Dots and Sarcosine Oxidase

In this study, a photobioelectrochemical sensor for the detection of sarcosine is reported. For this purpose, CdSe/ZnS quantum dot (QD) modified electrodes are prepared and the oxygen-dependent photocurrent is evaluated under illumination. By using sarcosine oxidase (SOD), the photocurrent can be suppressed because of biocatalytic oxygen reduction. For the construction of a sensor, SOD is immobilised on the QDs by means of the polyelectrolyte poly(allylamine hydrochloride) (PAH). Multi-layer systems have been built up to six bilayers through electrostatic interactions. The assembly can be verified by surface plasmon resonance measurements. By varying the number of layers, the influence of the amount of enzyme on the sensitivity of the sensor can be shown. The [SOD/PAH]6-layer system results in a signal change of 0.041% μM(-1) in the linear range from 100 μM to 1 mM of sarcosine.

Development of a fast and simple test system for the semiquantitative protein detection in cerebrospinal liquids based on gold nanoparticles.

The fast and simple detection of increased protein concentrations in cerebrospinal liquids is preferable in the emergency medicine and it can help to avoid unnecessary laboratory work by an early classification of neurological diseases. Here a test system is developed which is based on the electrostatic interaction between negatively charged gold nanoparticles and proteins at pH values around 5. The test system can be adjusted in such a way that protein/nanoparticles aggregates are formed leading to a red-shift in the absorption spectrum of the nanoparticles suspension. At concentrations above 500 mg/l the color of the suspension changes from red via violet toward blue in a rather small concentration range from 500 to 1000 mg/l. Furthermore the influence of various parameters such as gold nanoparticle concentration, pH value and varying ion concentration in the sample on the test system is examined. Finally cerebrospinal liquids of a larger number of patients have been analyzed.

Aqueous polythiophene electrosynthesis: A new route to an efficient electrode coupling of PQQ-dependent glucose dehydrogenase for sensing and bioenergetic applications

In this study, polythiophene copolymers have been used as modifier for electrode surfaces in order to allow the immobilization of active pyrroloquinoline quinone dependent glucose dehydrogenase (PQQ-GDH) and to simultaneously improve the direct electrical connection of the enzyme with the electrode. Polymer films are electrosynthesized in aqueous solution without the need of surfactants onto carbon nanotubes modified gold electrodes from mixtures of 3-thiopheneacetic acid (ThCH2CO2H) and 3-methoxythiophene (ThOCH3) using a potentiostatic pulse method. Polythiophene deposition significantly improves the bioelectrocatalysis of PQQ-GDH: the process starts at - 200 mV vs. Ag/AgCl and allows well-defined glucose detection at 0 V vs. Ag/AgCl with high current density. Several parameters of the electro-polymerization method have been evaluated to maximize the anodic current output after enzyme coupling. The polymer deposited by this new procedure has been morphologically and chemically characterized by different methods (SEM, EDX, FT-IR, UV-Vis, XPS and Raman spectroscopy). The bioelectrocatalytic response towards increasing glucose concentrations exhibits a dynamic range extending from 1 μM to 2 mM. The low applied potential allows to avoid interferences from easily oxidizable substances such as uric acid and ascorbic acid. Short and long-term stability has been evaluated. Finally, the PQQ-GDH electrode has been coupled to a bilirubin oxidase (BOD)- and carbon nanotube-based cathode in order to test its performance as anode of a biofuel cell. The promising results suggest a further investigation of this kind of polymers and, in particular, the study of the interaction with other enzymes in order to employ them in building up biosensors and biofuel cells.

Light-addressable amperometric electrodes for enzyme sensors based on direct quantum dot-electrode contacts

Quantum dots allow the generation of charge carriers upon illumination. When these particles are attached to an electrode a photocurrent can be generated. This allows their use as a light-switchable layer on the surface. The QDs can not only exchange electronics with the electrode, but can also interact with donor or acceptor compounds in solution providing access to the construction of signal chains starting from an analytic molecule. The magnitude and the direction of the photocurrent depend on several factors such as electrode polarization, solution pH and composition. These defined dependencies have been evaluated with respect to the combination of QD-electrodes with enzyme reactions for sensorial purpose. CdSe/ZnS-QD-modified electrodes can be used to follow enzymatic reactions in solution based on the oxygen sensitivity. In order to develop a photoelectrochemical biosensor, e.g. glucose oxidase is immobilized on the CdSe/ZnS-electrode. One immobilization strategy applies the layer-by-layer-technique of GOD and a polyelectrolyte. Photocurrent measurements of such a sensor show a clear concentration dependent behavior. The principle of combing QD oxidase. The sensitivity of quantum dot electrodes can be influenced by additional nanoparticles, but also by multiple layers of the QDs. In another direction of research it can be influenced by additional nanoparticles, but also by multiple layers of the QDs. In another direction of research it can be demonstrated that direct electron transfer from excited quantum dots can be achieved with the redox protein cytochrome c. This allows the detection of the protein, but also interaction partners such as a enzymes or superoxide.