@article{Halamek2005,
  author    = {Halamek, Jan},
  title     = {Sensitive detection of organophosphates in river water by means of a piezoelectric biosensor},
  year      = {2005},
  abstract  = {A highly sensitive piezoelectric biosensor has been developed for detection of cholinesterase inhibitors. The inhibitor benzoylecgonine-1,8-diamino-3,4-dioxaoctane (BZE-DADOO) was immobilized on a monolayer of 11- mercaptomonoundecanoic acid (MUA) self-assembled on the gold surface of the sensor. The binding of high-molecular-weight cholinesterase to the immobilized cocaine derivative was monitored with a mass sensitive piezoelectric quartz crystal (quartz crystal nanobalance; QCN). In the presence of an inhibiting substance in the sample, the binding of cholinesterase to the immobilized inhibitor was reduced. The decrease of the rate of mass change was proportional to the concentration of free inhibitor in the sample. This way the affinity sensor followed anti-cholinesterase toxicity and the enzyme activity of ChE was not addressed. A assay for detection of organophosphates (OP) was optimized. Regeneration of the sensor surface was achieved with 1 mol L-1 formic acid, which enabled 40 measurements with one sensor. All assays were carried out in a flow-through arrangement. The total measurement time (binding + regeneration) was 25 min and the detection limit for different OP (paraoxon, diisopropylfluorophosphate, chlorpyriphos, and chlorfenvinphos) was down to 10(-10) mol L-1 (0.02 mu g L-1). This sensor was used for determination of organophosphate (diisopropylfluorophosphate) levels in river water samples},
  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{LiuWollenbergerHalameketal.2005,
  author    = {Liu, Songqin and Wollenberger, Ursula and Halamek, Jan and Leupold, Eik and St{\"o}cklein, Walter F. M. and Warsinke, Axel and Scheller, Frieder W.},
  title     = {Affinity interaction betwen phenylboronic acid-carrying self-assembled monolayers and FAD or HRP},
  year      = {2005},
  abstract  = {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},
  language  = {en}
}