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Institute
The present work aimed to develop a new biochemical sensor based on a gold surface with well-defined structural nano-motifs.
The new anchor molecule 1,3-dimercaptopropan-2-ol was synthesized for this purpose. Due to its symmetrical structure with two thiol groups, it forms a very stable self-assembled monolayer (SAM) on the gold surface. The monolayers of 1,3-dimercaptopropan-2-ol were studied by cyclic voltammetry, impedance spectrometry, X-ray photoelectron spectroscopy (XPS), kinetics of capacitance and contact angle measurements. The structure of the SAM is determined by the adsorption conditions. The comparative study of the desorption of SAM shows that the stability of SAM increases when the molecules are mostly bound through both thiol groups.
The electrochemically active p-benzoquinone was immobilized on this monolayer. The 1,3- dimercaptopropan-2-ol served as an anchor molecule, 3-mercaptopropionic acid acted as a spacer, and 1,4-benzoquinone as a head group. The surface concentration of p-benzoquinone was 2.5 ± 0.2×10-10 mol•cm⁻². This corresponds to a functionalization of 65 ± 5% SAM molecules. The assembled layer can be used for electrically addressable immobilization of biomolecules or development of electrocatalytic sensors.
The SAM with terminal benzoquinone was used as a sensor for the quantitative detection of hydrogen peroxide. The sensor characterization was performed with cyclic voltammetry in the potential range from -0.6 V to +0.9 V as well as in the anodic or cathodic range only. The results indicate an oxidative electrochemical decomposition of the hydrogen peroxide at a potential of about +0.4 V with oxygen formation, while at cathodic potentials a reduction of the formed oxygen as well as of the hydrogen peroxide takes place. The reduction of the oxidation potential for hydrogen peroxide at the benzoquinone-coated gold electrode compared with the identical layer structure without benzoquinone indicates an electrocatalytic effect of this molecule in the oxidative decomposition of hydrogen peroxide.
The analytical evaluation of the sensor performance was performed in voltammetric as well as in amperometric mode. In the concentration range from 0.1 to 2.5 mM of hydrogen peroxide, the sensor response is linear, with a lower limit of detection of approximately 4 µM. The amperometric chemosensor shows good selectivity in the presence of typical interfering substances such as ascorbic acid, uric acid or glucose. The high sensitivity suggests that this system should not only be used as a hydrogen peroxide sensor, but also as a transducer for biosensors with immobilized oxidoreductases, such as a glucose biosensor with glucose oxidase.
Akustische Oberflächenwellen Geräte dienen als drahtlose Sensoren in verschiedenen Anwendungsgebieten. Neueste Forschungen zielen darauf ab diese Geräte als Temperatursensoren bei hohen Temperaturbereichen (T>300 °C) und in rauen Umgebungsbedingungen nutzbar zu machen. Entsprechend müssen herkömmliche Materialien, die für die Substrate und die interdigitalwandler Fingerelektroden verwendet werden, wie mehrschichtige Überzüge aus Al oder Cu, gegen Materialien die spezifische temperaturabhängige Effekte aufweisen ausgetauscht werden. Die Standardmethode des Elektronenstrahlverdampfens ist aufgrund der hohen Schmelzpunkte für das Auftragen von hochtemperaturstabilen Elektrodenmaterialien nicht geeignet. Kathodenzerstäubung ist eine weitere Beschichtungsmethode, die ohne Optimierung ebenfalls nicht für die lift-off Strukturierung geeignet ist. Aufgrund von sehr hohen Ar Gasdrücken von ca. 10-1 Pa kommt es zur Abscheidung an den Seitenwänden des Fotolacks, was zur Störung des lift-off Prozesses führt. In dieser Arbeit wurde das chemische Ätzen von Wolfram und Molybdän Dünnschichten als ein weiterer Schritt zwischen dem Kathodenzerstäuben, zum Beschichten von dünnen W bzw. Mo Fingerelektroden, und dem lift-off Prozess zur Entfernung der Seitenwandbeschichtung und der erfolgreichen Strukturierung der Interdigitalwandler untersucht.