@article{HalamekWollenbergerStoeckleinetal.2007, author = {Hal{\´a}mek, Jan and Wollenberger, Ursula and St{\"o}cklein, Walter F. M. and Warsinke, Axel and Scheller, Frieder W.}, title = {Signal amplification in immunoassays using labeling via boronic acid binding to the sugar moiety of immunoglobulin G : proof of concept for glycated hemoglobin}, issn = {0003-2719}, doi = {10.1080/00032710701327096}, year = {2007}, abstract = {A novel electrochemical immunoassay based on the multiple affinity labeling of the indicator antibody with an electro-active tag is presented. The concept is illustrated for the determination of the glycated hemoglobin HbA1c in hemoglobin samples. Hemoglobin is adsorbed to the surfactant-modified surface of a piezoelectric quartz crystal. Whereas the quartz crystal nanobalance is used to validate the total Hb binding, the HbA1c on the sensor surface is recognized by an antibody and quantified electrochemically after the sugar moieties of the antibody have been labeled in-situ with ferroceneboronic acid. The sensitivity of this sensor is about threefold higher than the sensitivity of a hemoglobin sensor, where the ferroceneboronic acid is bound directly to HbA1c.}, language = {en} } @article{HalamekWollenbergerStoeckleinetal.2007, author = {Hal{\´a}mek, Jan and Wollenberger, Ursula and St{\"o}cklein, Walter F. M. and Scheller, Frieder W.}, title = {Development of a biosensor for glycated hemoglobin}, issn = {0013-4686}, doi = {10.1016/j.electacta.2007.03.059}, year = {2007}, abstract = {The development of an electrochemical piezoelectric sensor for the detection of glycated hemoglobin is presented. The total hemoglobin (Hb) content is monitored with a mass-sensitive quartz crystal modified with surfactants, and the glycated fraction of the immobilized Hb is determined by subsequent voltarnmetric measurement of the coupled ferroceneboronic acid. Different modifications of the sensor were tested for their hemoglobin binding ability. Deoxycholate (DOCA) was found to be the most suitable among the examined modifiers. Piezoelectric quartz crystals with gold electrodes were modified with DOCA by covalent binding to a pre-formatted 4-aminothiophenol monolayer. The properties of the Hb binding to DOCA and the pH effect on this interaction were studied. In the proposed assay for glycated hemoglobin at first an Hb sample is incubated with ferroceneboronic acid (FcBA), which binds to the fructosyl residue of the glycated Hb. Then this preincubated Hb sample is allowed to interact with the DOCA-modified piezoelectric quartz crystal. The binding is monitored by quartz crystal nanobalance QCN). The amount of FcBA present on the sensor surface is determined by square wave voltammetry. The binding of FcBA results in well-defined peaks with an EO' of +200 mV versus Ag/AgC1 (1 M KC1). The peak height depends on the degree of glycated Hb in the sample ranging from 0\% to 20\% of total Hb. The regeneration of the sensing surface is achieved by pepsin digestion of the deposited Hb. Thus the sensor can be re-used more than 30 times.}, language = {en} } @article{HalamekTellerZeraviketal.2006, author = {Halamek, Jan and Teller, Carsten and Zeravik, Jiri and Fournier, Didier and Makower, Alexander and Scheller, Frieder W.}, title = {Characterization of binding of cholinesterases to surface immobilized ligands}, issn = {0003-2719}, doi = {10.1080/00032710600713107}, year = {2006}, abstract = {We summarize here the development of various piezoelectric biosensors utilizing cholinesterase (ChE) as the recognition element. In our work we studied the interaction between cholinesterase and its ligands (propidium, carnitine, benzylgonine-1,8-diamino-3,4-dioxaoctane (BZE-DADOO) and paraoxon). The sensor modification was based on a self-assembled monolayer (SAM) of a thiol compound (11-mercaptoundecanoic acid) on the gold electrode and the subsequent covalent coupling of the cholinesterase ligand to this SAM. The ligand-modified piezoelectric sensors were placed in a flow system to allow the on-line monitoring of cholinesterase binding and the enzymatic activity quantification by amperometry. Cholinesterases from different species-acetylcholinesterase (AChE) from Electrophorus electricus , AChE from Drosophila melanogaster , and butyrylcholinesterase (BChE) of human origin-were tested on the various immobilized ligands. Our research allowed the development of a competitive assay for the detection of organophosphates in river water samples using the BZE-DADOO-modified piezosensor. Another direction of research was pointed on the characterization of the interactions between ChE and its ligands. The kinetic binding constants were derived using a one- to-one binding model}, language = {en} } @article{HalamekTellerMakoweretal.2006, author = {Halamek, Jan and Teller, Carsten and Makower, Alexander and Fournier, Didier and Scheller, Frieder W.}, title = {EQCN-based cholinesterase biosensors}, issn = {0013-4686}, doi = {10.1016/j.electacta.2006.03.047}, year = {2006}, abstract = {The binding of acetylcholinesterase (AChE) to a propidium-modified piezoelectric quartz crystal and its surface enzymatic activity have been investigated. Propidium binds to a site remote to the active center of AChE - the peripheral anionic site (PAS) - which is located on the rim of the gorge to the active site. The gold electrodes of the quartz crystal were first modified with 11-mercaptoundecanoic acid to which propidium was coupled. AChE binding was monitored by a quartz crystal nanobalance (QCN), followed by amperometric activity evaluation of the AChE loaded on the sensor. Interestingly, the binding is strong but does not inhibit AChE. However, an excess of propidium in solution inhibits the immobilized enzyme. The surface enzymatic activities observed depend on the amount of enzyme and differ according to the type and species, i.e. number of enzyme subunits (Electrophorus electricus tetrameric, Drosophila melanogaster mono- and dimeric form - DmAChE). The operational stability and regeneration, effect of propidium in solution and detection limit for substrate for various AChEs were investigated amperometrically.}, language = {en} } @article{HalamekMakowerKnoescheetal.2005, author = {Halamek, Jan and Makower, Alexander and Kn{\"o}sche, Kristina and Skladal, Petr and Scheller, Frieder W.}, title = {Piezoelectric affinity sensors for cocaine and cholinesterase inhibitors}, year = {2005}, abstract = {We report here the development of piezoelectric affinity sensors for cocaine and cholinesterase inhibitors based on the formation of affinity complexes between an immobilized cocaine derivative and an anti-cocaine antibody or cholinesterase. For both binding reactions benzoylecgonine-1,8-diamino-3,4-dioxaoctane (BZE-DADOO) was immobilized on the surface of the sensor. For immobilization. pre-conjugated BZE-DADOO with 11-mercaptomonoundecanoic acid (MUA) via 2- (5-norbornen-2,3-dicarboximide)-1,1,3,3-tetramethyluronium-tetrafluoro borate (TNTU) allowed the formation of a chemisorbed monolayer on the piezosensor surface. The detection of cocaine was based oil a competitive assay. The change of frequency measured after 300 s of the binding reaction was used as the signal. The maximum binding of the antibody resulted in a frequency decrease of 35 Hz (with an imprecision 3\%, n = 3) while the presence of 100 pmol I-1 cocaine decreased the binding by 11\%. The limit of detection was consequently below 100 pmol I-1 for cocaine. The total time of one analysis was 15 min. This BZE-DADOO-modified sensor was adapted for the detection of organophosphates. BZE-DADOO - a competitive inhibitor - served as binding element for cholinesterase in a competitive assay. (C) 2004 Elsevier B.V. All rights reserved}, language = {en} } @article{GhindilisMakowerScheller1995, author = {Ghindilis, A. L. and Makower, Alexander and Scheller, Frieder W.}, title = {Laccase - glucose dehydrogenase recycling enzyme electrode based on potentiometric mediatorless electrocatalytic detection}, year = {1995}, language = {en} } @article{GhindilisMakowerScheller1995, author = {Ghindilis, A. L. and Makower, Alexander and Scheller, Frieder W.}, title = {Nanomolar determination of the ferrocene derivatives using a recycling enzyme electrode : development of the redox label immunoassay}, year = {1995}, language = {en} } @article{GhindilisMakowerScheller1995, author = {Ghindilis, A. L. and Makower, Alexander and Scheller, Frieder W.}, title = {Potentiometric enzyme electrodes based on substrate recycling and mediatorless bioelectrocatalysis}, year = {1995}, language = {en} } @article{GhindilisMakowerBaueretal.1995, author = {Ghindilis, A. L. and Makower, Alexander and Bauer, Christian G. and Bier, Frank Fabian and Scheller, Frieder W.}, title = {Determination of p-aminophenol and catecholamines at picomolar concentrations based on recycling enzyme amplification}, year = {1995}, language = {en} } @article{GeSchellerLisdat2003, author = {Ge, Bixia and Scheller, Frieder W. and Lisdat, Fred}, title = {Electrochemistry of immobilized CuZnSOD and FeSOD and their interaction with superoxide radicals}, year = {2003}, abstract = {Copper, zinc superoxide dismutase (CuZnSOD) from bovine erythrocytes and iron superoxide dismutase from Escherichia coli (FeSOD) were immobilized on 3-mercaptopropionic acid (MPA)-modified gold electrodes, respectively. The characterization of the SOD electrodes showed a quasi-reversible, electrochemical redox behavior with a formal potential of 47 {\~n} 4 mV and -154 {\~n} 5 mV (vs. Ag/AgCl, 1 M KCl) for surface adsorbed CuZnSOD and FeSOD, respectively. The heterogeneous electron transfer rate constants were determined to be about 65 and 35/s, respectively. Covalent fixation of both SODs was also feasible with only slight changes in the formal potential. The interaction of superoxide radicals (O2-) with the SOD electrode was investigated. No catalytic current could be observed. However, due to the fast cyclic reaction of SOD with superoxide, the communication of the protein with the electrode was strongly influenced. The amperometric detection of superoxide radicals is discussed.}, language = {en} }