88 results on '"Gerd-Uwe Flechsig"'
Search Results
2. Solar UV Photooxidation as Pretreatment for Stripping Voltammetric Trace Metal Analysis in River Water
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Gelaneh Woldemichael, Taffa Tulu, and Gerd-Uwe Flechsig
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Chemistry ,QD1-999 - Abstract
The application of solar ultraviolet radiation as sample pretreatment or preparation step in stripping voltammetric analysis of trace metals in presence of low levels of dissolved organic carbon (DOC) natural water samples (river water) was studied. River water samples were collected from downstream of Warnow river (Germany) and acidified to pH of 2±0.2 (by addition of 1 mL of ultrapure 65% HNO3 per liter sample). Furthermore, 100 μL/L of hydrogen peroxide solution (ultrapure, 30% H2O2) was added to the samples as photochemical reaction initiator. The samples were transferred to polyethylene terephthalate (PET) bottles and irradiated with solar radiation of UV-A intensity of 3.6 mW/m2 for six hours, and the concentrations of Zn, Cd, Pb, and Cu were determined by differential pulse anodic stripping voltammetry (DPASV). The comparison of the values with the results obtained for the original untreated sample and artificial UV-treated one proved that solar UV radiation can be applied to the digestion of dissolved organic carbon in trace metal analysis in natural waters like river water, lake waters, well waters, and so forth.
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- 2011
- Full Text
- View/download PDF
3. PCB based DNA detection chip.
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Stefan Gassmann, Holger Gotze, Matthias Hinze, Maren Mix, Gerd-Uwe Flechsig, and Lienhard Pagel
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- 2012
- Full Text
- View/download PDF
4. Voltammetric H/D Isotope Effects on Redox‐Active Small Molecules Conjugated with DNA Self‐Assembled Monolayers
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Sarasi K. K. Galagedera and Gerd-Uwe Flechsig
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chemistry.chemical_compound ,chemistry ,Kinetic isotope effect ,Electrochemistry ,Redox active ,Self-assembled monolayer ,Conjugated system ,Photochemistry ,Small molecule ,Voltammetry ,Catalysis ,DNA - Published
- 2019
5. Deuterium Isotope Effects Upon the Redox‐switching of the Viscosity of DNA Layers Observed by Electrochemical Quartz Crystal Micro‐balance
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Gerd-Uwe Flechsig and Sarasi K. K. Galagedera
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Crystal ,Viscosity ,Materials science ,Deuterium ,Kinetic isotope effect ,Electrochemistry ,Analytical chemistry ,Quartz ,Redox ,Viscoelasticity ,Analytical Chemistry - Published
- 2019
6. Amidyl Radical Directed Remote Allylation of Unactivated sp 3 C−H Bonds by Organic Photoredox Catalysis
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Lushun Wang, Ting Wang, Sonivette Colón-Rodríguez, Gerd-Uwe Flechsig, and Kui Wu
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organic chemicals ,food and beverages ,Photoredox catalysis ,General Medicine ,General Chemistry ,Medicinal chemistry ,Acceptor ,Catalysis ,Sulfone ,chemistry.chemical_compound ,chemistry ,Metal free ,Fragmentation (mass spectrometry) ,Amide ,Photocatalysis - Abstract
The development of visible-light-mediated allylation of unactivated sp3 C-H bonds is reported. The remote allylation was directed by the amidyl radical, which was generated by photocatalytic fragmentation of a pre-functionalized amide precursor. Both aromatic and aliphatic amide derivatives could successfully deliver the remote C-H allylation products in good yields. A variety of electron deficient allyl sulfone systems could be used as δ-carbon radical acceptor.
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- 2019
7. Amplified detection of single base mismatches with the competing-strand assay reveals complex kinetic and thermodynamic behavior of strand displacement at the electrode surface
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Maren Mix, Petr Orság, Ada Sedova, Katarzyna Biała, Gerd-Uwe Flechsig, Miroslav Fojta, and Katharina Bär
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0301 basic medicine ,Chemistry ,General Chemical Engineering ,Kinetics ,010402 general chemistry ,01 natural sciences ,Redox ,Displacement (vector) ,0104 chemical sciences ,03 medical and health sciences ,chemistry.chemical_compound ,030104 developmental biology ,Complementary sequences ,Osmium tetroxide ,Electrode ,Electrochemistry ,Biophysics ,Voltammetry ,DNA - Abstract
Detection of single-base mismatches with respect to a probe strand has been a predominant pursuit in electrochemical biosensor efforts, due to links found between single nucleotide polymorphisms (SNPs) and the predisposition to various diseases. We report an osmium tetroxide bipyridine-based, thermally-controlled, competitive-strand electrochemical assay to allow amplified detection of single-base mismatches. Optimally designed competitive-strand displacement and hybridization temperature allows us to distinguish the single-mismatched-target from the fully complementary sequence with unambiguous, highly reproducible, robust signal differences of over 90%. Furthermore, we find a complex interplay between the position of the redox label, variations in strand displacement kinetics due to mismatches incorporated into the competitive strand, and alterations in the melting temperature of DNA duplexes tethered on the gold surface, when probed by square-wave voltammetry. These insights will apply to any surface-tethered DNA-based electrochemical biosensor, and can help with understanding complex phenomena involved in these types of assays.
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- 2018
8. New electrode materials and devices for thermoelectrochemical studies and applications
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Gerd-Uwe Flechsig
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Nanostructure ,Materials science ,chemistry.chemical_element ,Nanotechnology ,02 engineering and technology ,Carbon nanotube ,010402 general chemistry ,021001 nanoscience & nanotechnology ,Tin oxide ,01 natural sciences ,0104 chemical sciences ,Analytical Chemistry ,Electrochemical cell ,law.invention ,Scanning electrochemical microscopy ,chemistry ,Thermocouple ,law ,Electrode ,Electrochemistry ,0210 nano-technology ,Carbon - Abstract
Summary Heated electrodes have been introduced a few decades ago to perform thermoelectrochemical investigations in a very flexible manner. This review considers unusual materials and devices that have been introduced recently to create new heated and also actively cooled electrodes: carbon paste with ionic liquids as binder, carbon nanotubes, iridium, Hg films, Bi films, Bi–Au alloys, gold nanostructures, and indium-doped tin oxide. Scanning electrochemical microscopy (SECM) based on thermocouple tips, as well as SECM of heated electrode arrays, and hot-tip-SECM have been proposed to study surfaces. Thermo-responsive layers allow for rapid switching of heated electrode surfaces. Recent years have seen a broad variety of thermoelectrochemical studies enabled by actively heated and cooled electrodes based on new materials. Very quick temperature changes and very high energy efficiency are two very distinct advantages of directly heated electrodes over both isothermal electrochemical cells and indirectly heated electrodes that suffer from high heat capacity.
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- 2018
9. Thermoelectrochemistry of Paracetamol - Studied at Directly Heated Micro-wire and Rotating Disk Electrodes
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Gerd-Uwe Flechsig, Johnsi Mathivanan, Zhihua Chang, and Sarasi K. K. Galagedera
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Chemical kinetics ,Materials science ,Electrode ,Electrochemistry ,02 engineering and technology ,Composite material ,010402 general chemistry ,021001 nanoscience & nanotechnology ,0210 nano-technology ,01 natural sciences ,0104 chemical sciences ,Analytical Chemistry - Published
- 2018
10. Voltammetric Detection of Thrombin by Labeling with Osmium Tetroxide Bipyridine and Binding with Aptamers on a Gold Electrode
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Alan A. Chen, Phensinee Haruehanroengra, Loan Huynh, Gerd-Uwe Flechsig, Sarasi K. K. Galagedera, Jia Sheng, Falko Wachholz, and Martin Jacobsen
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0301 basic medicine ,Thrombin-binding aptamer ,Aptamer ,010402 general chemistry ,01 natural sciences ,Combinatorial chemistry ,0104 chemical sciences ,Analytical Chemistry ,03 medical and health sciences ,chemistry.chemical_compound ,Bipyridine ,030104 developmental biology ,Thrombin ,Osmium tetroxide ,chemistry ,Hanging mercury drop electrode ,Electrode ,Adsorptive stripping voltammetry ,Electrochemistry ,medicine ,medicine.drug - Published
- 2018
11. Redox-Induced Switching of the Viscoelasticity of DNA Layers Observed by using Electrochemical Quartz Crystal Microbalance on the Millisecond Timescale
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Sarasi K. K. Galagedera, Gerd-Uwe Flechsig, and Jörg Peter
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Millisecond ,010405 organic chemistry ,Chemistry ,Quartz crystal microbalance ,010402 general chemistry ,Electrochemistry ,01 natural sciences ,Redox ,Catalysis ,Viscoelasticity ,0104 chemical sciences ,chemistry.chemical_compound ,Chemical engineering ,DNA - Published
- 2017
12. Sequence Detection of Unlabeled DNA Using the Sandwich Assay: Strand-Displacement, Hybridization Efficiency, and Probe- Conformation Considerations for the Tethered Surface
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Ada Sedova, Xiaoqi Ni, Hamdi Joda, Katarzyna Biała, and Gerd-Uwe Flechsig
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Analyte ,Oligonucleotide ,General Chemical Engineering ,Kinetics ,Analytical chemistry ,Chemical modification ,02 engineering and technology ,010402 general chemistry ,021001 nanoscience & nanotechnology ,01 natural sciences ,0104 chemical sciences ,chemistry.chemical_compound ,chemistry ,Duplex (building) ,Electrode ,Monolayer ,Electrochemistry ,Biophysics ,0210 nano-technology ,DNA - Abstract
We report the development of a “sandwich-hybridization” electrochemical DNA-detection assay on gold electrodes using osmium tetroxide-labeled reporter strands, while avoiding chemical modification of analyte strands. Successful design of the oligonucleotides used in the assay required a significant adjustment to solution-based estimates of melting temperature for the immobilized-probe/target duplex, to achieve optimal displacement kinetics. This allowed for reduced hybridization times and temperatures, and a higher sensitivity at low concentrations of DNA-analyte than oligos designed using solution-based melting temperatures as a guide. In addition we found that for the highest ranges of probe surface-density, signal response was sluggish until the DNA self-assembled monolayer (SAM) was exposed to several hybridization procedures, suggesting a modification of the SAM in response to a hybridization experiment. Use of a less-dense SAM eliminated this effect, suggesting increased influence of molecular crowding on the sandwich assay versus a simple hybridization. The high sensitivity, quick response time, relative simplicity and low cost demonstrated here helps pave the way for a field-level electrochemical genetic sensor using our method, as the unmodified target from samples in question can be tested directly without a chemical labeling step.
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- 2016
13. Rapid and Accurate Automatic Temperature Calibration of Disposable Screen-printed Heated Gold Electrodes
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Gerd-Uwe Flechsig, Juhaina Abdulkhalek, Gourav Bhowmik, Martin Schönhoff, Mengbing Huang, Tatiana Quiñones-Ruiz, Igor K. Lednev, Sonivette Colón-Rodríguez, Peter Langer, and Stephen W. Bentham
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Working electrode ,Chemistry ,General Chemical Engineering ,Potentiometric titration ,Bulk temperature ,Analytical chemistry ,02 engineering and technology ,010402 general chemistry ,021001 nanoscience & nanotechnology ,01 natural sciences ,Potentiostat ,0104 chemical sciences ,Analytical Chemistry ,Temperature gradient ,Electrical resistance and conductance ,Electrode ,Electrochemistry ,0210 nano-technology ,Temperature coefficient - Abstract
Joule-heated electrodes have been used to enhance electrochemical analysis. Due to such direct heating, a steep temperature gradient is created near the electrode surface. The heating device that provides the high-frequency AC (50 kHz or more) has to be calibrated, in order to apply the desired temperature during analysis. The applied temperature of the working electrode influences both its electrical resistance and the electrochemical potential of a redox couple. Open circuit potentiometric (OCP) measurements were performed automatically with screen-printed gold loop electrodes (Au-LE), while applying 50 kHz AC heating pulses of increasing intensity provided by a ThermaLab® AC generator. Potentiometric temperature calibrations were performed using 5 mM equimolar ferri/ferrocyanide in 0.1 M of potassium chloride at 20 °C bulk temperature. Potential differences produced during each heat pulse were used to automatically calculate the electrode temperature using the temperature coefficient of this redox couple (-1.6 mV/K). The electrode resistance values at each heating pulse were obtained by measuring the heating voltage and heating current. The automatic temperature calibration experiments with five Au-LEs were shown to be highly reproducible and precise, with an RSD for the temperature of 0.24% and 4% for resistance. The average margin error of OCP temperatures were ±0.66 K at a 95% confidence level. The temperature coefficient (α) of electrical resistivity of the screen-printed gold layers was found to be 0.0025 °C-1, which is 27% lower than the theoretical value for gold metal. These findings were confirmed by DC resistance measurements using a potentiostat. Comparing the OCP temperature with the resistivity method, the temperature difference was about 0.94 °C (2.8%). Both methods enable quick, reproducible and accurate temperature calibration for disposable Au-LE, which were also used for trace mercury detection in lake water samples
- Published
- 2019
14. The Osmium Tetroxide Bipyridine-labeled DNA Probe: Hairpin Conformations and Characterization of Redox-label Behavior
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Hamdi Joda, Ada Sedova, Waqas S. Awan, and Gerd-Uwe Flechsig
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Inorganic chemistry ,chemistry.chemical_element ,02 engineering and technology ,010402 general chemistry ,021001 nanoscience & nanotechnology ,01 natural sciences ,Combinatorial chemistry ,humanities ,0104 chemical sciences ,Analytical Chemistry ,chemistry.chemical_compound ,Bipyridine ,chemistry ,Osmium tetroxide ,Molecular beacon ,Covalent bond ,Electrochemistry ,Osmium ,0210 nano-technology ,Linker ,Biosensor ,DNA - Abstract
Osmium tetroxide bipyridine ([OsO4(bpy)]) is a versatile label for DNA electrochemistry. Here we report our efforts to create an osmium tetroxide-labeled immobilized DNA probe for use in biosensing experiments. Our label is applied in-house, as opposed to many other covalent redox labels used with DNA. We developed an on-electrode labeling method that was able to avoid attack of our disulfide-based linker by the [OsO4(bpy)]. Our results include two different hairpin-based signal-off hybridization detection assays, each with robust, reproducible signal decrease on binding to complementary target. We also found that 6-mercapto-1-hexanol was able to interact with [OsO4(bpy)] in a stable manner when assembled at the surface, but was able to remove excess [OsO4(bpy)], which was found to adsorb strongly to the gold surface, and avoid MCH transformation, when applied after the labeling process. Furthermore, we found an increased adsorption affinity of [OsO4(bpy)]-labeled DNA onto gold, characterized the redox behavior of adsorbed [OsO4(bpy)], and determined voltammetric signals on the HMDE of our intact disulfide linker while verifying that this linker is attacked by [OsO4(bpy)] when in solution.
- Published
- 2016
15. Nanostructured heated gold electrodes for DNA hybridization detection using enzyme labels
- Author
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Gerd-Uwe Flechsig, Frank Marken, Anne Walter, and Fanny Langschwager
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Working electrode ,Materials science ,Nanostructure ,Nanotechnology ,02 engineering and technology ,01 natural sciences ,Reference electrode ,chemistry.chemical_compound ,Materials Chemistry ,Ceramic ,Electrical and Electronic Engineering ,Instrumentation ,010401 analytical chemistry ,Metals and Alloys ,021001 nanoscience & nanotechnology ,Condensed Matter Physics ,0104 chemical sciences ,Surfaces, Coatings and Films ,Electronic, Optical and Magnetic Materials ,Microelectrode ,chemistry ,Chemical engineering ,visual_art ,Palladium-hydrogen electrode ,Electrode ,visual_art.visual_art_medium ,Ferrocyanide ,0210 nano-technology - Abstract
We report about two new types of nanostructured gold electrodes that can be heated electrically. At the directly heated gold micro-wire electrode, the microelectrode behavior is diminished upon galvanic deposition of gold nanostructures. The voltammetric waves observed with ferrocyanide turned into peaks. This suggests that it is the active electrode area rather than the mere geometric dimensions, what determines microelectrode behavior. Direct heating of this nanostructured gold wire electrode brought back the wave-like voltammogramms typical for microelectrodes. We also demonstrate with a second type of heated gold electrode, an indirectly heated sensor based on low temperature co-fired ceramics (LTCC), that DNA hybridization response of covalently attached enzyme labels is greatly improved by nanostructures. The voltammetric signal increase for the nanostructured electrode was 22-fold at 5 °C and 6-fold at 70 °C electrode temperature. We think that a trapping effect in the gold pores greatly increases sensitivity, in particular at lower electrode temperature.
- Published
- 2016
16. H/D Isotope Effects on Redox-Switching of DNA Self-Assembled Monolayers Observed by EQCM and Cyclic Voltammetry
- Author
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Sarasi K. K. Galagedera and Gerd-Uwe Flechsig
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Tris ,chemistry.chemical_compound ,chemistry ,Kinetic isotope effect ,Inorganic chemistry ,chemistry.chemical_element ,Quartz crystal microbalance ,Cyclic voltammetry ,Electrochemistry ,Voltammetry ,Redox ,Cobalt - Abstract
An electrochemical quartz crystal microbalance (EQCM) was employed to study the interactions of hexammine ruthenium(III) (RuHex) and hexammine cobalt(III) (CoHex) with a mixed self-assembled monolayer of single-stranded DNA and 6-mercapto-1-hexanol (ssDNA/MCH SAM) immobilized on gold electrodes. When the buffer medium was switched to deuterium oxide (D2O) from normal water (H2O), we observed a pronounced H/D kinetic isotope effect where a consistent shift of up to 400 mV was seen for the reduction peak potential of CoHex but not with RuHex. This was attributed to a 2400-fold change of the apparent reaction rate constant. Though there was a dramatic increase in the EQCM frequency response at a millisecond time scale in the presence of both redox indicators, compared to the signal observed in a low ionic strength buffer (10 mM tris(hydroxymethyl)aminomethane (Tris)/H2SO4 at pH 7.5), a 10 Hz decrease in the frequency shift was observed upon switching from H2O to D2O-based buffer medium. The hydrogen bond network within the ssDNA layer seems to amplify the H/D isotope effect with CoHex. Amplified isotope effects may play a role in living systems. The mechanisms of recently reported H/D isotope effects in medicinal and biochemistry are still widely unclear. Voltammetric and EQCM studies of H/D isotope effects can provide a platform to investigate amplified isotope effects not only with DNA layers, but probably also with proteins and small organic molecules and may be useful for studies of cell proliferation, as well as drug testing.
- Published
- 2018
17. Amidyl Radical Directed Remote Allylation of Unactivated sp
- Author
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Kui, Wu, Lushun, Wang, Sonivette, Colón-Rodríguez, Gerd-Uwe, Flechsig, and Ting, Wang
- Abstract
The development of visible-light-mediated allylation of unactivated sp
- Published
- 2018
18. The influence of the textural properties of ZnO nanoparticles on adsorption and photocatalytic remediation of water from pharmaceuticals
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J. Choina, Ch.-H. Fischer, Abdulaziz A. Bagabas, Axel Schulz, Ahmad S. Alshammari, Hendrik Kosslick, and Gerd-Uwe Flechsig
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Environmental remediation ,Inorganic chemistry ,Nanoparticle ,chemistry.chemical_element ,Substrate (chemistry) ,General Chemistry ,Zinc ,Catalysis ,Adsorption ,chemistry ,Chemical engineering ,Specific surface area ,Photocatalysis - Abstract
The pollution of surface, ground and drinking water by pharmaceuticals in low concentration is a new emerging problem. Zinc oxide nanoparticles of different sizes have been characterized by XRD, TEM, UV–Vis/DRS and N2 adsorption–desorption measurements. The photocatalytic degradation of low concentrated pharmaceuticals tetracycline and ibuprofen at low photocatalyst amount and at low photocatalyst to substrate mass ratio (cat-to-sub ratio) have been investigated in details. The influence of pH value, ZnO and drug concentrations as well as the contribution of adsorption has been deeply studied. The formation of intermediates has been investigated by electrospray ionization-time of flight-mass spectroscopy. Zinc oxide is known to promote the formation of reactive OH radicals and therefore is of special interest for the photocatalytic remediation of water from pharmaceuticals. Smaller particles are more active than larger ones due to increased specific surface area and adsorption. Interestingly, adsorption of the drug on ZnO is markedly improved at low concentration (
- Published
- 2015
19. Synthesis and Properties of 5,7-Dihydropyrido[3,2-b:5,6-b′]diindoles
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Tran Quang Hung, Ngo Ngoc Thang, Stefan Lochbrunner, Alexander Villinger, Peter Langer, Khurshid Ayub, Tuan Thanh Dang, Gerd-Uwe Flechsig, and Do Huy Hoang
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Ultraviolet visible spectroscopy ,Suzuki reaction ,Chemistry ,Computational chemistry ,Organic Chemistry ,Molecule ,Physical and Theoretical Chemistry ,Photochemistry ,Electrochemistry ,Quantum ,Fluorescence ,Coupling reaction ,Fluorescence spectroscopy - Abstract
5,7-Dihydropyrido[3,2-b:5,6-b′]diindoles were prepared by a highly efficient two-step synthesis that involved a site-selective Suzuki coupling reaction of 2,3,5,6-tetrabromopyridine and a subsequent Pd-catalyzed cyclization that proceeded through a twofold C–N coupling reaction with aromatic and aliphatic amines. With the exception of the parent molecule, which was described in a patent without any characterization data, the 5,7-dihydropyrido[3,2-b:5,6-b′]diindoles are a new chemical entity. Their electrochemical and photochemical properties were investigated. These pyridodiindoles show promising fluorescence properties with good quantum yields and interesting electrochemical behavior. The optical and electronical properties were analyzed and explained by using DFT calculations.
- Published
- 2014
20. Photocatalytic properties of Zr-doped titania in the degradation of the pharmaceutical ibuprofen
- Author
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Vu Anh Tuan, Gerd-Uwe Flechsig, Hendrik Kosslick, N.A. Tuyen, Ch.-H. Fischer, J. Choina, Nguyen Dinh Tuyen, and Axel Schulz
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inorganic chemicals ,Anatase ,Chemistry ,organic chemicals ,General Chemical Engineering ,Inorganic chemistry ,General Physics and Astronomy ,General Chemistry ,Chemical vapor deposition ,Reaction intermediate ,Mass spectrometry ,Catalysis ,Adsorption ,Polymerization ,Chemical engineering ,Photocatalysis - Abstract
Zr-doped titania of anatase structure type has been prepared by a combined sol–gel and chemical vapour deposition (CVD) process. The material has been characterized by XRD, TEM and chemical analysis. The photocatalytic performance has been investigated in the oxidative decomposition of the pharmaceutical ibuprofen (IBP) down to low ppm concentrations. The change of the composition of the reaction solution after photocatalytic treatment was followed by UV–Vis spectroscopy and GC/MS. Formation of reaction intermediates was studied by HPLC coupled electrospray ionization time-of-flight mass spectrometry ESI-TOF-MS. The catalytic performance has been studied by varying the catalyst and substrate concentration as well as changing the catalyst-to-substrate ratio. The influence of pH, adsorption and re-use of the catalyst has been tested. The results confirm the high catalytic activity of Zr-doped titania compared to pure titania at low catalyst loading. The material shows the improved textural mesoporosity. However, more reaction intermediates were formed, leading to faster deactivation of the photocatalyst. ESI-TOF-MS measurements point to the formation of a couple of reaction intermediates, which poison the catalyst.
- Published
- 2014
21. ToF-secondary ion mass-spectrometric study of copper deposition and stripping on directly heated screen-printed gold electrodes
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Aly M. Hafez, Ulrike Koch, and Gerd-Uwe Flechsig
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Auxiliary electrode ,Working electrode ,Ion beam ,Chemistry ,Analytical chemistry ,Condensed Matter Physics ,Underpotential deposition ,Reference electrode ,Secondary ion mass spectrometry ,Anodic stripping voltammetry ,Palladium-hydrogen electrode ,Electrochemistry ,General Materials Science ,Electrical and Electronic Engineering - Abstract
We report about a new kind of directly heated gold electrode. All electrodes including a directly heated gold loop electrode, a Ag pseudo reference, and a carbon counter electrode have been screen-printed on a ceramic alumina substrate. Thermal behaviour was studied by potentiometry using either an external or the integrated reference electrode. Stripping voltammetric copper signals were greatly improved at elevated deposition temperature. Secondary ion mass spectrometric studies (ToF-SIMS) revealed that different negative ionic species of copper complexes can be found on the gold electrode surface as a result of ion bombardment during SIMS analysis like Cu−, CuCl− and CuCl2 −. SIMS surface imaging using a fine focussed ion beam over the surface allowed us to obtain ion images (chemical maps) of the analyzed sample. SIMS depth profile analysis of the gold loop electrode was performed after copper deposition at room temperature (23 °C) and at 60 °C. CuCl2 − ion was used for the depth profile studies as it has shown the highest intensity among other observed species. Surface spectroscopic analysis, surface imaging and depth profile analysis have shown that the amount of deposited copper species on the gold loop electrode was increased upon increasing electrode temperature during the deposition step. Therefore, the presence of chloride in the solution will hinder underpotential deposition of Cu(0) and lead to badly defined and resolved stripping peaks.
- Published
- 2013
22. Photocatalytic decomposition of pharmaceutical ibuprofen pollutions in water over titania catalyst
- Author
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Axel Schulz, Ligia Frunza, Hendrik Kosslick, Ch.-H. Fischer, J. Choina, and Gerd-Uwe Flechsig
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inorganic chemicals ,Chemistry ,organic chemicals ,Process Chemistry and Technology ,Electrospray ionization ,Inorganic chemistry ,Reaction intermediate ,Mineralization (soil science) ,Mass spectrometry ,Catalyst poisoning ,Catalysis ,Photocatalysis ,Diffuse reflection ,General Environmental Science - Abstract
Due to the growing importance of low concentrated pollution of surface, ground and drinking, the photocatalytic decomposition of ibuprofen down to low ppm concentrations over titania catalyst has been investigated in detail. The catalyst was characterized by XRD, TEM, diffuse reflection UV–Vis and nitrogen adsorption measurement. The photocatalytic abatement of ibuprofen was monitored by UV–Vis spectrometry, chromatographic by GC/MS, and HPLC coupled electrospray ionization time-of-flight mass spectrometry (ESI-TOF-MS). Catalytic performance has been studied by varying the catalyst and substrate concentration as well as decreasing the catalyst-to-substrate mass ratio over a wide range. The photocatalytic treatment with titania catalyst leads to rapid mineralization of ibuprofen. Formation of intermediate reaction products has been investigated. It is proposed that intermediates in part form oligomeric species, which are responsible for catalyst poisoning. Additional, the influence of the pH value, oxygen supply and catalyst re-use have been checked.
- Published
- 2013
23. Hybridization Detection of Osmium Tetroxide Bipyridine-Labeled DNA and RNA on Heated Gold Wire Electrodes
- Author
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Gerd-Uwe Flechsig and Martin Jacobsen
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Chemistry ,Analytical chemistry ,RNA ,Combinatorial chemistry ,Analytical Chemistry ,chemistry.chemical_compound ,Bipyridine ,Osmium tetroxide ,Electrode ,Electrochemistry ,Nucleic acid ,Selectivity ,Voltammetry ,DNA - Abstract
We report about hybridization detection of different nucleic acids on capture probe-modified heated gold wire electrodes. We have compared three kinds of nucleic acid targets: DNA, uracil-conjugated DNA, and RNA. All three sorts of nucleic acids targets could be labeled with osmium tetroxide bipyridine, hybridized with immobilized DNA capture probes and then detected by square-wave voltammetry. Heating the gold electrode instead of the entire bulk hybridization solution leads to improved hybridization efficiency in most cases. The reason could be found in a thermal micro-stirring effect around the heated wire electrode. Also selectivity was improved. Mismatches could be discriminated for DNA and uracil-conjugated DNA targets. Mismatches in RNA strands, however, are more difficult to detect due to relatively stable secondary structures.
- Published
- 2012
24. Direct electrochemistry of horseradish peroxidase immobilized in a chitosan-[C4mim][BF4] film: determination of electrode kinetic parameters
- Author
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Annette-E. Surkus, Gregory G. Wildgoose, Richard G. Compton, Gerd-Uwe Flechsig, Debbie S. Silvester, and Jenny S. Long
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Inorganic chemistry ,Biophysics ,Ionic Liquids ,Activation energy ,Biosensing Techniques ,Electrochemistry ,Horseradish peroxidase ,chemistry.chemical_compound ,Electron transfer ,Borates ,Physical and Theoretical Chemistry ,Voltammetry ,Electrodes ,Horseradish Peroxidase ,Chitosan ,Aqueous solution ,biology ,Imidazoles ,General Medicine ,Hydrogen-Ion Concentration ,Enzymes, Immobilized ,Kinetics ,chemistry ,Ionic liquid ,biology.protein ,Thermodynamics ,Cyclic voltammetry ,Oxidation-Reduction - Abstract
The direct electrochemistry of a HRP–chi–[C 4 mim][BF 4 ] film (where HRP = horseradish peroxidase, chi = chitosan, and [C 4 mim][BF 4 ] = the room temperature ionic liquid (RTIL) 1-butyl-3-methylimidazolium tetrafluoroborate) has been studied by cyclic voltammetry on a glassy carbon electrode. The mechanism for the electrochemical reaction of HRP is suggested to be EC for the reduction, and CE for the following re-oxidation, as the oxidative peak potential remained approximately unchanged across the scan rate range. The half wave potential of HRP reduction was found to be pH dependent, suggesting that a concomitant proton and electron transfer is occurring. Using theoretical simulations of the experimentally obtained peak positions, the standard electron transfer rate constant, k 0 , was found to be 98 (± 16) s − 1 at 295 K in pH 7 phosphate buffer solution, which is very close to the value reported in the absence of ionic liquid. This suggests that the ionic liquid used here in the HRP–chi–[C 4 mim][BF 4 ]/GC electrode does not enhance the rate of electron transfer. k 0 was found to increase systematically with increasing temperature and followed a linear Arrhenius relation, giving an activation energy of 14.20 kJ mol − 1 . The electrode kinetics and activation energies obtained are identical to those reported for HRP films in aqueous media. This leads us to question if the use of RTIL films provide any unique benefits for enzyme/protein voltammetry. Rather the films may likely contain aqueous zones in which the enzymes are located and undergo electron transfer.
- Published
- 2016
25. Solar UV-assisted sample preparation of river water for ultra-trace determination of uranium by adsorptive stripping voltammetry
- Author
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Taffa Tulu, Gerd-Uwe Flechsig, and Gelaneh Woldemichael
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chemistry.chemical_compound ,chemistry ,Chloranilic acid ,Environmental chemistry ,Adsorptive stripping voltammetry ,Dissolved organic carbon ,chemistry.chemical_element ,Sample preparation ,Irradiation ,Uranium ,River water ,Voltammetry ,Analytical Chemistry - Abstract
The article describes how solar ultraviolet-A radiation can be used to digest samples as needed for voltammetric ultratrace determination of uranium(VI) in river water. We applied adsorptive stripping voltammetry (AdSV) using chloranilic acid as the complexing agent. Samples from the river Warnow in Rostock (Germany) were pretreated with either soft solar UV or wit artificial hard UV from a 30-W source emitting 254-nm light. Samples were irradiated for 12 h, and both methods yielded the same results. We were able to detect around 1 μg·L−1 of uranium(VI) in a sample of river water that also contained dissolved organic carbon at a higher mg·L−1 levels. No AdSV signal was obtained for U(VI) without any UV pre-treatment. Pseudo-polarographic experiments confirmed the dramatic effect of both digestion techniques the the AdSV response. The new method is recommended for use in mobile ultratrace voltammetry of heavy metals for most kinds of natural water samples including tap, spring, ground, sea, and river waters. The direct use of solar radiation for sample pre-treatment represents a sustainable technique for sample preparation that does not consume large quantities of chemicals or energy.
- Published
- 2012
26. Electrochemical detection of 0.6% genetically modified maize MON810 in real flour samples
- Author
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Simone Krüger, Julia Rüger, Maren Mix, Inge Broer, and Gerd-Uwe Flechsig
- Subjects
Genetically modified maize ,Oligonucleotide ,Transgene ,Electrochemical detection ,lcsh:Chemistry ,chemistry.chemical_compound ,chemistry ,Osmium tetroxide ,Biochemistry ,lcsh:Industrial electrochemistry ,lcsh:QD1-999 ,Electrochemistry ,Gene ,Biosensor ,DNA ,lcsh:TP250-261 - Abstract
We demonstrate an approach for the electrochemical detection of genetically modified maize in real maize flour samples by means of square-wave voltammetry (SWV). After labeling the asymmetric PCR-amplified targets with osmium tetroxide bipyridine [OsO4(bipy)], they were hybridized with immobilized oligonucleotide probes on gold electrodes. We could detect the maize genes ivrp and SSIIb in near isogenic maize. The transgene cryIa/b and the MON810 specific fragment were detected in all transgenic maize samples, down to a content of 0.6% of MON810 in mixed samples. While it was possible to detect all sequences in the samples containing 100% near isogenic or respectively transgenic maize after a hybridization time of less than 10 min, a hybridization time of 30 min was necessary for the detection of the genetic modifications in samples containing only 0.9 to 0.6% of transgenic maize. No significant detection of the transgene cryIa/b or MON810 was possible when only 0.5% of transgenic maize was present in the sample, most likely due to insufficient amplification of the template DNA. Keywords: Electrochemical DNA sensor, Hybridization, Gold electrode, Osmium tetroxide bipyridine, Real sample, Maize MON810
- Published
- 2012
27. Electrically Heated Electrodes: Practical Aspects and New Developments
- Author
-
Anne Walter and Gerd-Uwe Flechsig
- Subjects
Chemistry ,Capillary action ,Electrode ,Electrochemistry ,Analytical chemistry ,Electrochemiluminescence ,Nanotechnology ,Electric current ,Electrophoreses ,Analytical Chemistry - Abstract
This article comprehensively reviews a selected subfield of thermoelectrochemistry, which bases upon joule-heated working electrodes. Both directly and indirectly heated electrodes are considered. In all cases, an electric current (AC or DC) is used to elevate the electrode temperature during the electrochemical processes. The development of joule-heated electrodes started as early as 1966 and was greatly accelerated by Grundler et al. since 1993. However, during the last 5 years the development became even faster, when other groups started to contribute novel approaches and designs on how to implement electrically heated electrodes in capillary electrophoreses and spectroelectrochemistry. To date there are more than 90 publications on heated electrodes.
- Published
- 2011
28. Temperature Control in Electrochemical DNA Sensing
- Author
-
Martin Jacobsen and Gerd-Uwe Flechsig
- Subjects
Combinatorics ,chemistry.chemical_compound ,Temperature control ,Materials science ,Chemical engineering ,chemistry ,General Earth and Planetary Sciences ,Electrochemistry ,DNA ,Earth-Surface Processes ,Electrochemical gas sensor ,General Environmental Science - Published
- 2011
29. Functionalized Micromachines for Selective and Rapid Isolation of Nucleic Acid Targets from Complex Samples
- Author
-
Joseph Wang, Susana Campuzano, Gerd-Uwe Flechsig, Filiz Kuralay, Daniel Kagan, and Shankar Balasubramanian
- Subjects
Serum ,DNA, Complementary ,Time Factors ,Lysis ,Bioengineering ,Biosensing Techniques ,Urine ,Motion ,chemistry.chemical_compound ,Nucleic acid thermodynamics ,Drug Delivery Systems ,Nucleic Acids ,Escherichia coli ,Biological fluids ,Humans ,General Materials Science ,Oligonucleotide Array Sequence Analysis ,Ions ,Extramural ,Mechanical Engineering ,Nucleic Acid Hybridization ,DNA ,General Chemistry ,Condensed Matter Physics ,Selective isolation ,Isolation (microbiology) ,Microscopy, Fluorescence ,chemistry ,Biochemistry ,Nucleic acid - Abstract
The transport properties of single-strand DNA probe-modified self-propelling micromachines are exploited for "on-the-fly" hybridization and selective single-step isolation of target nucleic acids from "raw" microliter biological samples (serum, urine, crude E. coli lysate, saliva). The rapid movement of the guided modified microrockets induces fluid convection, which enhances the hybridization efficiency, thus enabling the rapid and selective isolation of nucleic acid targets from untreated samples. The integration of these autonomous microrockets into a lab-on-chip device that provides both nucleic acid isolation and downstream analysis could thus be attractive for diverse applications.
- Published
- 2011
30. Redox cycling amplified electrochemical detection of DNA hybridization: Application to pathogen E. coli bacterial RNA
- Author
-
Gerd-Uwe Flechsig, Joseph Wang, David A. Haake, Jie Wu, and Anne Walter
- Subjects
Streptavidin ,Phosphatase ,Enzyme electrode ,Biotin ,Biosensing Techniques ,Nicotinamide adenine dinucleotide ,Aminophenols ,medicine.disease_cause ,Biochemistry ,Article ,Analytical Chemistry ,chemistry.chemical_compound ,Limit of Detection ,Benzoquinones ,Escherichia coli ,medicine ,Environmental Chemistry ,Electrodes ,Spectroscopy ,Detection limit ,Sulfur Compounds ,Nucleic Acid Hybridization ,DNA ,Alkaline Phosphatase ,Enzymes, Immobilized ,NAD ,RNA, Bacterial ,chemistry ,Gold ,Imines ,NAD+ kinase ,Oxidation-Reduction - Abstract
An electrochemical genosensor in which signal amplification is achieved using p-aminophenol (p-AP) redox cycling by nicotinamide adenine dinucleotide (NADH) is presented. An immobilized thiolated capture probe is combined with a sandwich-type hybridization assay, using biotin as a tracer in the detection probe, and streptavidin-alkaline phosphatase as reporter enzyme. The phosphatase liberates the electrochemical mediator p-AP from its electrically inactive phosphate derivative. This generated p-AP is electrooxidized at an Au electrode modified self-assembled monolayer to p-quinone imine (p-QI). In the presence of NADH, p-QI is reduced back to p-AP, which can be re-oxidized on the electrode and produce amplified signal. A detection limit of 1 pM DNA target is offered by this simple one-electrode, one-enzyme format redox cycling strategy. The redox cycling design is applied successfully to the monitoring of the 16S rRNA of E. coli pathogenic bacteria, and provides a detection limit of 250 CFU μL(-1).
- Published
- 2011
31. Removal of hazardous pharmaceutical from water by photocatalytic treatment
- Author
-
Gerd-Uwe Flechsig, Hendrik Kosslick, A. W. Morawski, Axel Schulz, Vu Anh Tuan, J. Choina, and Heiko Duwensee
- Subjects
Pollutant ,Chemistry ,Tetracycline ,General Chemistry ,cyclic voltammetry ,Catalysis ,Adsorption ,Wastewater ,low concentration ppb range ,Environmental chemistry ,Materials Chemistry ,medicine ,Photocatalysis ,Water treatment ,titania ,tetracycline abatement ,Water pollution ,photocatalysis ,QD1-999 ,medicine.drug - Abstract
The photocatalytic abatement of hazardous pharmaceuticals has been investigated at very low concentration in the ppb range as found in wastewater and in environmental pollutants. Photocatalytic degradation of tetracycline as a model compound with titania catalysts has been studied using solarium UV-A and black light with differentially applied electric power, tetracycline and catalyst concentration. Abatement of up to 90% has been achieved after 1 hour. Adsorption of tetracycline and photochemical degradation contribute significantly to the abatement of tetracycline resulting in an immediate reduction during the initial period of treatment. Contribution of adsorption is high at very low concentration (500 ppb). Photocatalytic treatment with titania is even highly efficient in the abatement of very small concentrations of tetracycline in drinking water.
- Published
- 2010
32. Sequence-specific electrochemical detection of nucleic acids in real samples
- Author
-
Gerd-Uwe Flechsig, Maren Mix, and Heiko Duwensee
- Subjects
Biochemistry ,Chemistry ,Nucleic acid ,Electrochemical biosensor ,Sequence (biology) ,Nanotechnology ,Electrochemical detection ,Blood or Tissue ,DNA microarray - Abstract
This paper reviews past and current developments in the field of electrochemical biosensors with a focus on the sequence-specific detection of nucleic acids in real samples. After electrochemical hybridization sensors had been first described in 1993, it took nearly a decade until some of the many proposed protocols were indeed applied to real samples like blood or tissue. Electrochemical transduction schemes used either rely on electroactive moieties such as intercalators, groove binders, covalently attached labels, and products of enzyme markers or they are completely indicator free like impedance-based detection principles. Most detection schemes require a polymerase chain reaction amplification step to allow for sufficient selectivity and sensitivity. Today, several companies develop electrochemical microarrays able to detect dozens to many thousands of sequences in a single experiment.
- Published
- 2010
33. Directly Heated Bismuth Film Electrodes Based on Gold Microwires
- Author
-
Heiko Duwensee, Martin Jacobsen, Gerd-Uwe Flechsig, Miriam Adamovski, and Falko Wachholz
- Subjects
Materials science ,Inorganic chemistry ,Analytical chemistry ,chemistry.chemical_element ,Picric acid ,Tartrate ,Electrochemistry ,Buffer (optical fiber) ,Amperometry ,Analytical Chemistry ,Bismuth ,chemistry.chemical_compound ,chemistry ,Electrode ,Cyclic voltammetry - Abstract
As a nontoxic substitute for mercury electrodes, bismuth electrodes attained a lot of attention during the last years. In this report we describe for the first time the preparation of two different directly heatable bismuth-modified microwire electrodes. We characterized the electrochemical behaviour using cyclic voltammetry in acetate buffer and alkaline tartrate solution. The bismuth electrodes show a significantly wider potential window compared with bare gold wires. In the presence of picric acid as one example for the detection of explosives, the bismuth electrodes deliver higher signals. By applying heat during the measurements, the signals can be enhanced further. We used the temperature pulse amperometry (TPA) technique to improve the electrochemical response at the different types of electrodes. In this preliminary study, we were able to detect 3 ppm traces of picric acid.
- Published
- 2010
34. Cover Feature: Redox-Induced Switching of the Viscoelasticity of DNA Layers Observed by using Electrochemical Quartz Crystal Microbalance on the Millisecond Timescale (ChemElectroChem 3/2018)
- Author
-
Jörg Peter, Sarasi K. K. Galagedera, and Gerd-Uwe Flechsig
- Subjects
Millisecond ,Materials science ,Quartz crystal microbalance ,Electrochemistry ,Redox ,Catalysis ,Viscoelasticity ,chemistry.chemical_compound ,chemistry ,Feature (computer vision) ,Chemical physics ,Cover (algebra) ,DNA - Published
- 2018
35. Template-Free Galvanic Nanostructuring of Gold Electrodes for Sensitive Electrochemical Biosensors
- Author
-
Gerd-Uwe Flechsig, Michael Zwanzig, Heiko Duwensee, Jan Gimsa, Falko Wachholz, Stefan Fiedler, Ralf Schmidt, and Publica
- Subjects
Materials science ,Oxide ,Nanotechnology ,Active surface ,Analytical Chemistry ,Electrochemical gas sensor ,chemistry.chemical_compound ,chemistry ,Electrode ,Electrochemistry ,Galvanic cell ,Surface modification ,Cyclic voltammetry ,Voltammetry - Abstract
Gold nanostructuring of smooth gold disk-electrodes has been performed by electrodeposition. FE-SEM images indicate a strongly enlarged electrochemically active surface of the modified electrodes. This could be approved by the gold oxide reduction peak in cyclic voltammetry. The electrodes were also applied for sequence-specific DNA detection. For this, complementary single stranded capture probes were immobilized on the electrodes and consecutively hybridized with complementary and noncomplementary [OsO4(bipy)]-labeled DNA targets. We found that intermediate dehybridization steps did not decrease the sensitivity for the specific target. Moreover, the surface modification increased the voltammetric signal by an approx. factor of 9. Further, an enhanced linear calibration range was observed. The presented simple nanostructuring process holds great promise for many electrochemical sensor applications.
- Published
- 2009
36. Kinetics of the labeling reactions of thymine, cytosine and uracil with osmium tetroxide bipyridine
- Author
-
Annette-Enrica Surkus, Gerd-Uwe Flechsig, Thomas Reske, and Heiko Duwensee
- Subjects
chemistry.chemical_compound ,Bipyridine ,Osmium tetroxide ,chemistry ,Pyrimidine ,Nucleic acid ,Uracil ,Photochemistry ,Combinatorial chemistry ,DNA ,Cytosine ,Analytical Chemistry ,Thymine - Abstract
The electroactive complex osmium tetroxide bipyridine holds great promise as a covalent label for biosensor applications regarding nucleic acids and protein detection. Labeling can easily be performed in the laboratory. Until now, almost only DNA species have been investigated using this label. Thymine (which occurs exclusively in DNA) is known to react much faster than cytosine and uracil. In order to explore the possibilities to modify and detect also RNA species in a timely fashion, we have investigated the kinetics of reactions of osmium tetroxide bipyridine with the pyrimidine bases in the micromolar concentration range at different temperatures by means of spectrophotometry. Results were confirmed using voltammetric detection for the determination of labeled oligonucleotides. The modification reaction can be easily completed at room temperature within 7 h, even in case of cytosine and uracil. At 60 °C, 3 h are sufficient for complete modification of all pyrimidine bases that are found in natural nucleic acids. These findings will be important for future biosensor applications with RNA species as target molecules.
- Published
- 2009
37. Electrochemical detection of modified maize gene sequences by multiplexed labeling with osmium tetroxide bipyridine
- Author
-
Maren Mix, Gerd-Uwe Flechsig, Heiko Duwensee, and Inge Broer
- Subjects
Stereochemistry ,Oligonucleotide ,Nucleic acid sequence ,Thymine ,lcsh:Chemistry ,Bipyridine ,chemistry.chemical_compound ,lcsh:Industrial electrochemistry ,lcsh:QD1-999 ,chemistry ,Osmium tetroxide ,Electrochemistry ,Voltammetry ,Cytosine ,DNA ,lcsh:TP250-261 - Abstract
In this report we demonstrate an approach for the electrochemical detection of four sequences from maize and genetically modified (GM) maize by means of square-wave voltammetry (SWV). After multiplexed labeling with osmium tetroxide bipyridine ([OsO4(bipy)]), the target oligonucleotides are hybridized with a complementary DNA capture probe immobilized on gold electrodes. The multiplexed labeling was performed by mixing the four target strands with the respective oligonucleotides 80% homologous to the central target recognition sequences in order to protect the latter from binding of [OsO4(bipy)] to its thymine or cytosine residues. All components were added to the same solution. No significant decreases in SWV hybridization signals were observed after such multiplexed labeling of up to four target strands in the same reaction batch. Obtained voltammetric signals were significantly higher at 50 °C compared to 25 °C hybridization temperature and very low response was observed for non-complementary strands. Multiplexed labeling with osmium tetroxide bipyridine holds great promise for the development of simple and effective voltammetric detection protocols for GM organisms. Keywords: Assorted labeled targets, Square-wave voltammetry, SWV, Osmium tetroxide bipyridine, Covalent DNA-label, Electrochemical hybridization detection, Genetically modified maize
- Published
- 2009
38. Thermal Modulation of Nanomotor Movement
- Author
-
Daniel Kagan, Percy Calvo-Marzal, Kalayil Manian Manesh, Gerd-Uwe Flechsig, Shankar Balasubramanian, and Joseph Wang
- Subjects
Hot Temperature ,Yield (engineering) ,Materials science ,Transducers ,Nanowire ,Nanotechnology ,Sensitivity and Specificity ,Biomaterials ,Motion ,Viscosity ,Thermal ,Electrochemistry ,General Materials Science ,Nanomotor ,Platinum ,Range (particle radiation) ,Reproducibility of Results ,Equipment Design ,General Chemistry ,Motion control ,Nanostructures ,Equipment Failure Analysis ,Transducer ,Chemical physics ,Gold ,Biotechnology - Abstract
Motion control is essential for various applications of man-made nanomachines. The ability to control and regulate the movement of catalytic nanowire motors is illustrated by applying short heat pulses that allow the motors to be accelerated or slowed down. The accelerated motion observed during the heat pulses is attributed primarily to the thermal activation of the redox reactions of the H(2)O(2) fuel at the Pt and Au segments and to the decreased viscosity of the aqueous medium at elevated temperatures. The thermally modulated motion during repetitive temperature on/off cycles is highly reversible and fast, with speeds of 14 and 45 microm s(-1) at 25 and 65 degrees C, respectively. A wide range of speeds can be generated by tailoring the temperature to yield a linear speed-temperature dependence. Through the use of nickel-containing nanomotors, the ability to combine the thermally regulated motion of catalytic nanomotors with magnetic guidance is also demonstrated. Such on-demand control of the movement of nanowire motors holds great promise for complex operations of future manmade nanomachines and for creating more sophisticated nanomotors.
- Published
- 2009
39. Numerically optimized shape of directly heated electrodes for minimal temperature gradients
- Author
-
Ursula van Rienen, Nico Mahnke, Heiko Duwensee, Aleksandar Markovic, Gerd-Uwe Flechsig, and Falko Wachholz
- Subjects
Convection ,Surface (mathematics) ,Materials science ,Metals and Alloys ,Analytical chemistry ,Mechanics ,Condensed Matter Physics ,Surfaces, Coatings and Films ,Electronic, Optical and Magnetic Materials ,Conductor ,Pulse (physics) ,Temperature gradient ,Electrode ,Materials Chemistry ,Development (differential geometry) ,Electrical and Electronic Engineering ,Current (fluid) ,Instrumentation - Abstract
For electrochemical investigations at heated electrodes especially in the bioanalytical area a precise control of the surface temperature is necessary. Due to the problem of non-homogenous temperature allocation over the length of a directly heated electrode/conductor in electrochemical applications the possibility of changing its design in order to avoid such inhomogeneous effects was investigated. By mathematical simulations with the program Comsol Multiphysics©, concerning the temperature development along a conducting wire for different oval shapes depending on changing heating durations and current densities, the temperature gradient could be minimized. We could show the possibility to achieve an almost homogenous surface temperature by creating a special oval-shaped design for the electrode. The convection of surrounding media in the proximity of the conductor was not taken into account for the thermal simulation, which applies in particular for short-term pulse heating.
- Published
- 2009
40. Electrochemical detection of osmium tetroxide-labeled PCR-products by means of protective strands
- Author
-
Maren Mix, Thomas Reske, Hubert Bahl, and Gerd-Uwe Flechsig
- Subjects
Time Factors ,Pyridines ,Analytical chemistry ,DNA, Single-Stranded ,chemistry.chemical_element ,Electrochemistry ,Polymerase Chain Reaction ,Analytical Chemistry ,Bipyridine ,chemistry.chemical_compound ,Organometallic Compounds ,Osmium ,Electrodes ,Voltammetry ,Staining and Labeling ,Chemistry ,DNA–DNA hybridization ,Temperature ,Combinatorial chemistry ,Exodeoxyribonucleases ,Oligodeoxyribonucleotides ,Osmium tetroxide ,Covalent bond ,Gold ,DNA Probes ,DNA - Abstract
This communication reports about how single-stranded 136 base polymerase chain reaction (PCR) products labeled with electrochemically active osmium tetroxide bipyridine can be detected voltammetrically by hybridization with probe strands immobilized on gold electrodes. These electroactive ssDNA targets have been obtained by means of Lambda Exonuclease treatment of the double-stranded PCR products followed by hybridization of the remaining single strands with short protective strands and covalent labeling with osmium tetroxide bipyridine. Square-wave voltammetric signals of these osmium labels have been obtained only upon hybridization with the immobilized probe strands. An optimal 50 degrees C hybridization temperature has been found with a saturation of the probe layer at 30 min hybridization time and 7.5 nmol/l target concentration. The blank capture probe layer alone did not yield any signal. Unprotected strands produced almost no interference. Such double-selective switch-on electrochemical hybridization assays hold great promise for the specific detection of PCR products.
- Published
- 2007
41. Temperature pulse modulated amperometry at compact electrochemical sensors
- Author
-
Katarzyna Biala, Falko Wachholz, Gerd-Uwe Flechsig, and Magdalena Piekarz
- Subjects
Flow injection analysis ,Auxiliary electrode ,Calibration curve ,Analytical chemistry ,Picric acid ,Signal ,Amperometry ,lcsh:Chemistry ,chemistry.chemical_compound ,Capillary electrophoresis ,chemistry ,lcsh:Industrial electrochemistry ,lcsh:QD1-999 ,Electrode ,Electrochemistry ,lcsh:TP250-261 - Abstract
This communication reports about thermal modulation of amperometric signals by short heat pulses applied at directly heated gold electrodes. A gold layer together with a pseudo reference and counter electrode has been printed onto a low temperature cofired ceramic (LTCC) substrate. We chose hexacyanoferrate(II) and picric acid as model analytes in this preliminary study. Peak shaped amperometric signals were formed upon such thermal modulation. The peak current has been taken as the analytical information. Thermal modulation in amperometric measurements activates kinetically inhibited analytes such as picric acid. A linear calibration plot has been obtained ranging from 0.2 to 1 mmol/l. The background contribution was effectively suppressed, even at −0.7 V applied potential at the gold electrode. Convection did not significantly affect the analytical signal. This will be important for applications where convection is pulsating or is otherwise not under control and thus induces disturbances. Future applications include environmental monitoring, flow injection analysis, high performance liquid chromatography and capillary electrophoresis. Keywords: LTCC, Amperometry, Temperature pulse, Heated electrode, Picric acid
- Published
- 2007
42. A Compact and Versatile Instrument for Radio Frequency Heating in Nonisothermal Electrochemical Studies
- Author
-
Jan Gimsa, Harald Grabow, Gerd-Uwe Flechsig, Falko Wachholz, Peter Gründler, and Heiko Duwensee
- Subjects
Materials science ,Working electrode ,business.industry ,Analytical chemistry ,Glassy carbon ,Inductor ,Potentiostat ,Analytical Chemistry ,Electrode ,Dielectric heating ,Electrochemistry ,Bridge circuit ,Optoelectronics ,Cyclic voltammetry ,business - Abstract
We describe a novel instrument and electrical circuit for sensitive electrochemical measurements at simultaneous direct electrode heating. The new measuring principle can be applied to working electrodes of various designs featuring two end contacts. In our experiments, the contacts were connected to a 100 kHz AC heating power supply and the potentiostat via the new inductor bridge circuit. A compact heating-generator housing contains all components necessary for sine wave generation as well as amplification and transformation of the heating power. The new arrangement yields high temperature cyclovoltammetric signals for the [Fe(CN)6]3−/4− redox system with a noise level superior to the earlier symmetrically branched wire electrode designs. Noise and disturbances are dramatically suppressed especially for high resistance electrodes such as glassy carbon electrodes. Without a center contact, the working electrode design is greatly simplified. This opens new opportunities for the design of a great variety of heated electrodes that may be arranged in arrays or consist of materials with relatively high resistivity such as carbon and conducting polymers.
- Published
- 2007
43. Electrochemical Detection of DNA Hybridization by Means of Osmium Tetroxide Complexes and Protective Oligonucleotides
- Author
-
Gerd-Uwe Flechsig and and Thomas Reske
- Subjects
Detection limit ,Base Sequence ,Osmium Tetroxide ,Oligonucleotide ,DNA–DNA hybridization ,Molecular Sequence Data ,Oligonucleotides ,Nucleic Acid Hybridization ,DNA ,Electrochemistry ,Combinatorial chemistry ,Analytical Chemistry ,chemistry.chemical_compound ,Osmium tetroxide ,chemistry ,Biochemistry ,Potentiometry ,Denaturation (biochemistry) ,Voltammetry ,Thymine - Abstract
We have utilized protective oligonucleotides to modify DNA fragments with osmium tetroxide complexes without compromising their ability to hybridize with immobilized thiol-linked probe-SAMs on gold electrodes. Due to reversible voltammetric signals of Os(VI/IV), this method allowed sensitive electrochemical hybridization detection of short (25 bases) and long (120 bases) thymine-containing DNA targets. The detection limit was 3.2 nM for the long target. We found an optimum 40 degrees C hybridization temperature for the short target. No interference by noncomplementary DNA was observed. At least 10 repetitive hybridization experiments at the same probe-SAM were possible with thermal denaturation in between. Such use of protective strands could be useful also for other types of DNA recognition and even for other DNA-modifying agents. Moreover, it is possible to produce electrochemically active oligonucleotides (targets and reporter probes) in ones own laboratory in a simple way.
- Published
- 2007
44. Sequence and Temperature Influence on Kinetics of DNA Strand Displacement at Gold Electrode Surfaces
- Author
-
Katarzyna Biała, Gerd-Uwe Flechsig, and Ada Sedova
- Subjects
Materials science ,Base Sequence ,Oligonucleotide ,Base Pair Mismatch ,Pyridines ,Transition temperature ,Kinetics ,Analytical chemistry ,Nucleic Acid Hybridization ,Activation energy ,DNA ,Diffusion ,Microelectrode ,Nucleic acid thermodynamics ,Chemical physics ,Electrode ,Organometallic Compounds ,Transition Temperature ,General Materials Science ,Gold ,DNA Probes ,Electrodes - Abstract
Understanding complex contributions of surface environment to tethered nucleic acid sensing experiments has proven challenging, yet it is important because it is essential for interpretation and calibration of indispensable methods, such as microarrays. We investigate the effects of DNA sequence and solution temperature gradients on the kinetics of strand displacement at heated gold wire electrodes, and at gold disc electrodes in a heated solution. Addition of a terminal double mismatch (toehold) provides a reduction in strand displacement energy barriers sufficient to probe the secondary mechanisms involved in the hybridization process. In four different DNA capture probe sequences (relevant for the identification of genetically modified maize MON810), all but one revealed a high activation energy up to 200 kJ/mol during hybridization, that we attribute to displacement of protective strands by capture probes. Protective strands contain 4 to 5 mismatches to ease their displacement by the surface-confined probes at the gold electrodes. A low activation energy (30 kJ/mol) was observed for the sequence whose protective strand contained a toehold and one central mismatch, its kinetic curves displayed significantly different shapes, and we observed a reduced maximum signal intensity as compared to other sequences. These findings point to potential sequence-related contributions to oligonucleotide diffusion influencing kinetics. Additionally, for all sequences studied with heated wire electrodes, we observed a 23 K lower optimal hybridization temperature in comparison with disc electrodes in heated solution, and greatly reduced voltammetric signals after taking into account electrode surface area. We propose that thermodiffusion due to temperature gradients may influence both hybridization and strand displacement kinetics at heated microelectrodes, an explanation supported by computational fluid dynamics. DNA assays with surface-confined capture probes and temperature gradients should not neglect potential influences of thermodiffusion as well as sequence-related effects. Furthermore, studies attempting to characterize surface-tethered environments should consider thermodiffusion if temperature gradients are involved.
- Published
- 2015
45. ChemInform Abstract: Synthesis and Properties of 5,7-Dihydropyrido[3,2-b:5,6-b′]diindoles
- Author
-
Peter Langer, Ngo Ngoc Thang, Stefan Lochbrunner, Alexander Villinger, Gerd-Uwe Flechsig, Do Huy Hoang, Tran Quang Hung, Khurshid Ayub, and Tuan Thanh Dang
- Subjects
Suzuki reaction ,Chemistry ,Computational chemistry ,Molecule ,General Medicine ,Electrochemistry ,Quantum ,Fluorescence ,Coupling reaction ,Characterization (materials science) - Abstract
5,7-Dihydropyrido[3,2-b:5,6-b′]diindoles were prepared by a highly efficient two-step synthesis that involved a site-selective Suzuki coupling reaction of 2,3,5,6-tetrabromopyridine and a subsequent Pd-catalyzed cyclization that proceeded through a twofold C–N coupling reaction with aromatic and aliphatic amines. With the exception of the parent molecule, which was described in a patent without any characterization data, the 5,7-dihydropyrido[3,2-b:5,6-b′]diindoles are a new chemical entity. Their electrochemical and photochemical properties were investigated. These pyridodiindoles show promising fluorescence properties with good quantum yields and interesting electrochemical behavior. The optical and electronical properties were analyzed and explained by using DFT calculations.
- Published
- 2015
46. Self-assembled monolayers on bismuth electrodes
- Author
-
Miriam Adamovski, Gerd-Uwe Flechsig, Peter Gründler, and Agnieszka Zając
- Subjects
Chemistry ,Inorganic chemistry ,chemistry.chemical_element ,Self-assembled monolayer ,Electrochemistry ,digestive system diseases ,Bismuth ,lcsh:Chemistry ,lcsh:Industrial electrochemistry ,lcsh:QD1-999 ,Electrode ,Monolayer ,Cyclic voltammetry ,Voltammetry ,Biosensor ,lcsh:TP250-261 - Abstract
This communication reports about preliminary studies of self-assembled monolayers (SAMs) on bismuth bulk electrodes (BiBEs) using daunomycin and picric acid as electrochemical indicators. The cyclic voltammetric signals of these indicators decreased after the modification of the bismuth electrode with alkanethiols, indicating the formation of SAMs on bismuth. Signal decrease as well as the stability of the SAMs depends strongly upon the length of the alkanethiol. The bismuth-based SAMs were significantly more stable at negative potentials than SAMs on a gold substrate, yielding an useful potential range from −0.3 V to −1.3 V. Such highly stable SAMs could be beneficial for trace metal detection and biosensors. Keywords: Bismuth bulk electrode, Self-assembled monolayer, SAM, Voltammetry, Daunomycin, Picric acid
- Published
- 2006
47. Principles and Analytical Applications of Heated Electrodes
- Author
-
Gerd-Uwe Flechsig and Peter Gründler
- Subjects
Acceleration ,Boiling point ,Nucleic acid quantitation ,Chemistry ,Electrode ,Analytical chemistry ,Nanochemistry ,Nanotechnology ,Electrolyte ,Electrochemistry ,Microwave ,Analytical Chemistry - Abstract
This article reviews the development of the various heated electrodes, heating devices and their analytical applications which have been published during the last decades. Generally spoken, electrode heating can provide different positive effects on electrochemical measurements: mass transport enhancement, reaction kinetics acceleration and the removal of deposited substances from the electrode surface. This often leads to remarkably improved signal-to-noise characteristics in electroanalytical chemistry. Short heat pulses or direct heating of very small electrolyte compartments allow for temperatures far above the boiling point of the solution. Major application fields include trace metal and nucleic acids analysis. Future development will result in miniaturized selectively heated electrode arrays.
- Published
- 2006
48. ChemInform Abstract: Palladium Catalyzed Synthesis and Physical Properties of Indolo[2,3-b]quinoxalines
- Author
-
Ngo Ngoc Thang, Tran Quang Hung, Alexander Villinger, Khurshid Ayub, Tuan Thanh Dang, Gerd-Uwe Flechsig, Do Huy Hoang, Stefan Lochbrunner, Peter Langer, and Aleksej Friedrich
- Subjects
chemistry.chemical_compound ,Annulation ,Quinoxaline ,chemistry ,Suzuki reaction ,Band gap ,chemistry.chemical_element ,Substrate (chemistry) ,General Medicine ,Electrochemistry ,Medicinal chemistry ,Palladium ,Catalysis - Abstract
A series of indolo[2,3-b]quinoxaline derivatives were efficiently synthesized from 2,3-dibromoquinoxaline by two pathways. A one-pot approach using Pd-catalyzed two-fold C–N coupling and C–H activation reactions gave indolo[2,3-b]quinoxaline derivatives in good yields, but with limited substrate scope. In addition, a two-step approach to indolo[2,3-b]quinoxalines was developed which is based on Pd-catalyzed Suzuki coupling reactions and subsequent annulation by Pd-catalyzed two-fold C–N coupling with aromatic and aliphatic amines. The electrochemical and photochemical properties of indolo[2,3-b]quinoxaline derivatives were investigated. These studies show that 6-(4-methoxyphenyl)-6H-indolo[2,3-b]quinoxaline showed the highest HOMO energy level and lowest band gap.
- Published
- 2014
49. Electrochemistry of nicotinamide adenine dinucleotide (reduced) at heated platinum electrodes
- Author
-
Joseph Wang, Peter Gründler, Carolin Lau, and Gerd-Uwe Flechsig
- Subjects
Nicotinamide ,Inorganic chemistry ,Analytical chemistry ,chemistry.chemical_element ,Nicotinamide adenine dinucleotide ,Electrochemistry ,Biochemistry ,Amperometry ,Analytical Chemistry ,chemistry.chemical_compound ,chemistry ,Electrode ,Environmental Chemistry ,Platinum ,Voltammetry ,Biosensor ,Spectroscopy - Abstract
This paper reports on the electrochemical behavior and determination of nicotinamide adenine dinucleotide reduced (NADH) at indirectly electrically heated platinum electrodes. At room temperature, a surface fouling can be observed during voltammetric and amperometric measurements, whereas a slight electrode heating during the measurements greatly minimizes such electrode passivation. This is illustrated by repetitive cyclic and square-wave voltammetric scans as well as using amperometry. The effect of electrode temperature and NADH concentration is evaluated. Amperometric calibration data exhibit a 10-fold higher sensitivity upon elevating the electrode temperature from 22 to 75 °C. Furthermore, the amperometric response at the hot Pt-electrode is very stable, with 86% of the initial activity remaining after 20 min stirring of 5 mM NADH (compared to 32% under cold conditions). This represents the first example of using heated electrodes for minimizing surface fouling effects. The ability of heated Pt-electrodes to promote the NADH electron-transfer reaction suggests great promise for dehydrogenase-based amperometric biosensors.
- Published
- 2005
50. Ex situ atomic force microscopy of bismuth film deposition at carbon paste electrodes
- Author
-
Peter Gründler, Mike Kienbaum, and Gerd-Uwe Flechsig
- Subjects
Aqueous solution ,Analytical chemistry ,chemistry.chemical_element ,Electrolyte ,Electrochemistry ,Bismuth ,Carbon paste electrode ,lcsh:Chemistry ,chemistry ,lcsh:Industrial electrochemistry ,lcsh:QD1-999 ,Electrode ,Deposition (phase transition) ,Composite material ,Carbon ,lcsh:TP250-261 - Abstract
This paper describes how the surface of an oil–graphite based carbon paste electrode (CPE) can be studied by means of atomic force microscopy (AFM). By choosing the scanning parameters very carefully, it is possible to scan even such a soft and delicate surface. Both intermittent contact and phase shift scan modes provide useful information about nano-distribution of topographical details as well as hard and soft areas on the surface. The electrochemical bismuth film deposition from a 0.05 M sulphuric acid +1 ppm Bi(III) containing electrolyte can be investigated by both scan modes. Intermittent scan mode yields very thin (2 nm) layer-shaped structures sizing from 20 nm to some microns. Phase shift scans of the same sections depict extensive areas of high and uniform phase shift, which cannot be found on the bare CPE, and thus have to be attributed to the newly formed bismuth film. AFM holds great promise for the investigation of all kinds of carbon paste electrodes. Keywords: Carbon paste electrode, CPE, Bismuth film electrode, BiFE, Atomic force microscopy, AFM
- Published
- 2005
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