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Capacitive field-effect electrolyte-insulator-semiconductor sensors consisting of an Al-p-Si-SiO2 structure have been used for the electrical detection of unlabelled single- and double-stranded DNA (dsDNA) molecules by their intrinsic charge. A simple functionalization protocol based on the layer-by-layer (LbL) technique was used to prepare a weak polyelectrolyte/probe-DNA bilayer, followed by the hybridization with complementary target DNA molecules. Due to the flat orientation of the LbL-adsorbed DNA molecules, a high sensor signal has been achieved. In addition, direct label-free detection of in-solution hybridized dsDNA molecules has been studied.
Miniaturized setup, compatibility with advanced micro- and nanotechnologies, and ability to detect biomolecules by their intrinsic molecular charge favor the semiconductor field-effect platform as one of the most attractive approaches for the development of label-free DNA chips. In this work, a capacitive field-effect EIS (electrolyte–insulator–semiconductor) sensor covered with a layer-by-layer prepared, positively charged weak polyelectrolyte layer of PAH (poly(allylamine hydrochloride)) was used for the label-free electrical detection of DNA (deoxyribonucleic acid) immobilization and hybridization. The negatively charged probe single-stranded DNA (ssDNA) molecules were electrostatically adsorbed onto the positively charged PAH layer, resulting in a preferentially flat orientation of the ssDNA molecules within the Debye length, thus yielding a reduced charge-screening effect and a higher sensor signal. Each sensor-surface modification step (PAH adsorption, probe ssDNA immobilization, hybridization with complementary target DNA (cDNA), reducing an unspecific adsorption by a blocking agent, incubation with noncomplementary DNA (ncDNA) solution) was monitored by means of capacitance–voltage and constant-capacitance measurements. In addition, the surface morphology of the PAH layer was studied by atomic force microscopy and contact-angle measurements. High hybridization signals of 34 and 43 mV were recorded in low-ionic strength solutions of 10 and 1 mM, respectively. In contrast, a small signal of 4 mV was recorded in the case of unspecific adsorption of fully mismatched ncDNA. The density of probe ssDNA and dsDNA molecules as well as the hybridization efficiency was estimated using the experimentally measured DNA immobilization and hybridization signals and a simplified double-layer capacitor model. The results of field-effect experiments were supported by fluorescence measurements, verifying the DNA-immobilization and hybridization event.
Inhalt
07 Der Stoff, aus dem die Träume sind | Modedesigner, Fotograf, Künstler : der FH-Absolvent Hans W. Krämer
12 Wurzeln, die tief zurückreichen | Die Handwerker- und Kunstgewerbeschule Aachen
18 Eine einmalige Chance | Der japanische Gastwissenschaftler Prof. Dr. Ko-ichiro Miyamoto forscht ein Jahr lang am Campus Jülich
22 Pionierarbeit auf leisen Sohlen | Vier junge Marokkanerinnen sind die ersten Absolventinnen des internationalen Studiengangs Angewandte Chemie
26 Gute Hacker - Böse Hacker| FH Aachen bietet Kurse zum ethischen Hacken an
28 Eiffelturm meets Kartenhaus | Architekturstudierende entwickeln ausgefuchstes Stecksystem für temporäre Architektur
32 Dom in 3-D | Fachbereich Bauingenieurwesen vermisst das Aachener Welterbe
36 "Müssen Behinderte denn Auto fahren?!" | FH-Absolventinnen gründen Fahrschule für Menschen mit Handicap
40 Im Innern des "Blutenden Gletschers" | Fünf Wochen lang lebten und arbeiteten FH-Ingenieure in der größten Eiswüste der Erde
46 Das ist mein Zuhause | Nach über 40 Jahren verlässt Prof. Dr. Horst Heinrichs die FH Aachen
50 Die Qual der Wahl | Mit dem "Guten Studienstart" ins Ingenieurstudium
52 Fachtutorenschulung an der FH Aachen
55 Zusammen wachsen | Neue Schnittstelle: Erste Studierende machen ihren Master in Energiewirtschafts-Informatik
56 Pro8 geht in die achte Runde | Studierende stellen sich Herausforderungen aus der Industrie
58 Auf die Messe, fertig, los! | Alumnus Moritz Christ gibt der Euregio Wirtschaftsschau ein neues Gesicht
61 Unsere EM wird 75: Die FH wünscht alles Gute!
61 Herzlichen Glückwunsch! Alt-Rektor Prof. Buchkremer wird 75
62 FH Aachen kooperiert mit Ford | Hannover Messe: FH präsentiert drei Projekte | FH Aachen ausgezeichnet : Zertifikat 2014 Vielfalt gestalten in NRW
63 Impressum
An enzyme-based multi-parameter biosensor is developed for monitoring the concentration of formate, d-lactate, and l-lactate in biological samples. The sensor is based on the specific dehydrogenation by an oxidized β-nicotinamide adenine dinucleotide (NAD+)-dependent dehydrogenase (formate dehydrogenase, d-lactic dehydrogenase, and l-lactic dehydrogenase, respectively) in combination with a diaphorase from Clostridium kluyveri (EC 1.8.1.4). The enzymes are immobilized on a platinum working electrode by cross-linking with glutaraldehyde (GA). The principle of the determination scheme in case of l-lactate is as follows: l-lactic dehydrogenase (l-LDH) converts l-lactate into pyruvate by reaction with NAD+. In the presence of hexacyanoferrate(III), the resulting reduced β-nicotinamide adenine dinucleotide (NADH) is then regenerated enzymatically by diaphorase. The electrochemical detection is based on the current generated by oxidation of hexacyanoferrate(II) at an applied potential of +0.3 V vs. an Ag/AgCl reference electrode. The biosensor will be electrochemically characterized in terms of linear working range and sensitivity. Additionally, the successful practical application of the sensor is demonstrated in an extract from maize silage.