TY - JOUR A1 - Scheller, Frieder W. A1 - Lisdat, Fred A1 - Wollenberger, Ursula T1 - Application of electrically contacted enzymes for biosensors Y1 - 2005 SN - 3-527- 30690-0 ER - TY - JOUR A1 - Scheller, Frieder W. A1 - Bistolas, Nikitas A1 - Liu, Songqin A1 - Jänchen, Michael A1 - Katterle, Martin A1 - Wollenberger, Ursula T1 - Thirty years of haemoglobin electrochemistry N2 - Electrochemical investigations of the blood oxygen carrier protein include both mediated and direct electron transfer. The reaction of haemoglobin (Hb) with typical mediators, e.g., ferricyanide, can be quantified by measuring the produced ferrocyanide which is equivalent to the Hb concentration. Immobilization of the mediator within the electrode body allows reagentless electrochemical measuring of Hb. On the other hand, entrapment of the protein within layers of polyclectrolytes, lipids, nanoparticles of clay or gold leads to a fast heterogeneous electron exchange of the partially denatured Hb. (c) 2005 Elsevier B.V. All rights reserved Y1 - 2005 ER - TY - JOUR A1 - Mak, Wing Cheung A1 - Cheung, Kwan Yee A1 - Trau, Dieter A1 - Warsinke, Axel A1 - Scheller, Frieder W. A1 - Renneberg, Reinhard T1 - Electrochemical bioassay utilizing encapsulated electrochemical active microcrystal biolabels N2 - A new approach to perform electrochemical immunoassay based on the utilization of encapsulated microcrystal was developed. The microcrystal labels create a "supernova effect" upon exposure to a desired releasing agent. The microcrystal cores dissolve, and large amounts of signal-generating molecules diffuse across the capsule wall into the outer environment. Layer-by-Layer (LbL) technology was employed for the encapsulation of electrochemical signal- generating microcrystals (ferrocene microcrystals). The encapsulated microcrystals were conjugated with antibody molecules through the adsorption process. The biofunctionalized microcrystals were utilized as a probe for immunoassays. The microcrystal-based label system provided a high-signal molecule to antibody (SIP) ratio of 10(4)-10(5). Microcrystal biolabels with different antibody surface coverage (1.60-5.05 mg m(-2)) were subjected to a solid-phase immunoassay for the detection of mouse immunoglobulin G (M-IgG) molecules. The microcrystal-based immunoassay for the detection of M-IgG performed with microcrystals having antibody surface coverage of 5.05 mg m(-2) showed a sensitivity of 3.93 nA g(- 1) L-1 with a detection limit of 2.82 g L-1 Y1 - 2005 SN - 0003-2700 ER - TY - JOUR A1 - Liu, Songqin A1 - Wollenberger, Ursula A1 - Halamek, Jan A1 - Leupold, Eik A1 - Stöcklein, Walter F. M. A1 - Warsinke, Axel A1 - Scheller, Frieder W. T1 - Affinity interaction betwen phenylboronic acid-carrying self-assembled monolayers and FAD or HRP N2 - A method is provided for the recognition of glycated molecules based on their binding affinities to boronate- carrying monolayers. The affinity interaction of flavin adenine dinucleotide (FAD) and horseradish peroxidase (HRP) with phenylboronic acid monolayers on gold was investigated by using voltammetric and microgravimetric methods. Conjugates of 3-aminopherrylboronic acid and 3,3'-dithiodipropionic acid di(N-hydroxysuccinimide ester) or 11-mercaptoundecanoic acid were prepared and self-assembled on gold surfaces to generate monolayers. FAD is bound to this modified sur-face and recognized by a pair of redox peaks with a formal potential of -0.433 V in a 0.1 m phosphate buffer solution, pH 6.5. Upon addition of a sugar to the buffer, the bound FAD could be replaced, indicating that the binding is reversible. Voltammetric, mass measurements, and photometric activity assays show that the HRP can also be bound to the interface. This binding is reversible, and HRP can be replaced by sorbitol or removed in acidic solution. The effects of pH, incubation time, and concentration of H2O2 were studied by comparing the catalytic reduction of H2O2 in the presence of the electron-donor thionine. The catalytic current of the HRP-loaded electrode was proportional to HRP concentrations in the incubation solution in the range between 5 mu g mL(-1) and 0.4 mg mL(-1) with a linear slope of 3.34 mu A mL mg(-1) and a correlation coefficient of 0.9945 Y1 - 2005 ER - TY - JOUR A1 - Halamek, Jan A1 - Makower, Alexander A1 - Knösche, Kristina A1 - Skladal, Petr A1 - Scheller, Frieder W. T1 - Piezoelectric affinity sensors for cocaine and cholinesterase inhibitors N2 - 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 Y1 - 2005 ER - TY - JOUR A1 - Bistolas, Nikitas A1 - Wollenberger, Ursula A1 - Jung, Christiane A1 - Scheller, Frieder W. T1 - Cytochrome P450 biosensors : a review N2 - Cytochrome P450 (CYP) is a large family of enzymes containing heme as the active site. Since their discovery and the elucidation of their structure, they have attracted the interest of scientist for many years, particularly due to their catalytic abilities. Since the late 1970s attempts have concentrated on the construction and development of electrochemical sensors. Although sensors based on mediated electron transfer have also been constructed, the direct electron transfer approach has attracted most of the interest. This has enabled the investigation of the electrochemical properties of the various isoforms of CYP. Furthermore, CYP utilized to construct biosensors for the determination of substrates important in environmental monitoring, pharmaceutical industry and clinical practice. (c) 2004 Elsevier B. V. All rights reserved Y1 - 2005 ER -