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As a consequence of organophosphorus (OP) toxins posing a threat to human life globally, organophosphorus hydrolase (OPH) has become the enzyme of choice to detoxify such compounds. Organophosphorus hydrolase was covalently immobilized onto a quartz substrate for utilization in paraoxon detection. The substrate was cleaned and modified prior to chemical attachment. Each modification step was monitored by imaging ellipsometry as the thickness increased with each modification step. The chemically attached OPH was labeled with a fluorescent dye (7-isothiocyanato-4-methylcoumarin) for the detection of paraoxon in aqueous solution, ranging from 10(-9) to 10(-5) M. UV-visible spectra were also acquired for the determination of the hydrolysis product of para-oxon, namely p-nitrophenol.

Langmuir film properties, UV-vis spectroscopy, epifluorescence microscopy, and transmission electron microscopy were used to study CdSe quantum dots (QDs) in 2D. By combining these results, it was possible to determine the molar absorptivity, limiting nanoparticle area, luminescence property, and arrangement of the QDs in the monolayer films at the air-water interface. Either trioctylphosphine oxide (TOPO) or 1-octadecanethiol (ODT) stabilized the QDs. The data collected reveal that TOPO forms close-packed monolayers on the surface of the QDs and that ODT-stabilized QDs undergo alkyl chains interdigitation. It was also found that varying the nanoparticle size, nature of surfactant, surface pressure, and mixed monolayers could help engineer the 2D self-assembly of the QDs at the air-water interface. Of practical importance is the transfer of these monolayer films onto hydrophilic or hydrophobic solid substrates, which could be successfully accomplished via the Langmuir-Blodgett film deposition technique.

Organophosphorus acid anhydrolases (OPAA; E.C.3.1.8.2) are a class of enzymes that hydrolyze a variety of toxic acetylcholinesterase-inhibiting organophosphorus (OP) compounds, including pesticides and fluorine-containing chemical nerve agents. In this paper, subphase conditions have been optimized to obtain stable OPAA Langmuir films, and the diisopropylfluorophosphate (DFP) hydrolysis reaction catalyzed by OPAA in aqueous solution and at the air-water interface was studied. OPAA-DFP interactions were investigated utilizing different spectroscopic techniques, that is, circular dichroism and fluorescence in aqueous solution and infrared reflection absorption spectroscopies at the air-water interface. The characterization of OPAA and its secondary structure in aqueous solution and as a monolayer at the air-water interface in the absence and in the presence of DFP dissolved in aqueous solution or in the aqueous subphase demonstrated significantly distinctive features. The research described herein demonstrated that OPAA can be used in an enzyme-based biosensor for DFP detection.

The secondary structure of organophosphorus hydrolase (OPH) has been studied with circular dichroism (CD) spectroscopy in the far-UV region. The effect of pH on the secondary structure of OPH solution was examined over the pH range from 3.56 to 9.60. As shown on the CD spectra, the secondary structure of OPH is well defined when the pH value is near the isoelectric point (7.6); however, it is destroyed when the pH values are increased or decreased further. This is explained by the loss of helical structure. The pH effect on CD spectra contributes to clarify the optimum pH needed to obtain a stable OPH Langmuir film at the air−water interface and its correlation to the secondary structure of the enzyme. Comparative study of the thermal treatment on the secondary structure of OPH in solution, Langmuir−Blodgett film, and dry film shows that the molecular arrangement plays a dominant role in the thermal stability of OPH. With use of the CDPro software package a quantitative estimation of the secondary structu...

Layer-by-layer (LbL) assembly has been utilized to fabricate an ultrathin film of polyelectrolytes. The architecture was composed of chitosan and organophosphorus hydrolase polycations along with thioglycolic acid-capped CdSe quantum dots (QDs) as the polyanion. The topography of the films was studied using epifluorescence microscopy imaging. The photoluminescence property of the functionalized QDs improved when sandwiched between the polycation layers. The enhanced optical property of QDs allowed easy monitoring of LbL growth and detection of paraoxon with high sensitivity. The presence of organophosphorus compounds was confirmed through UV−vis and emission spectroscopies.

The aim of this study is to immobilize an enzyme, namely, organophosphorus hydrolase (OPH), and to detect the presence of paraoxon, which is an organophosphorus compound, using the layer-by-layer (LbL) deposition technique. To lift the OPH from the solid substrate, a pair of polyelectrolytes (positively charged chitosan (CS) and negatively charged poly(thiophene-3-acetic acid) (PTAA)) were combined. These species were made charged by altering the pH of the solutions. LbL involved alternate adsorption of the oppositely charged polyions from dilute aqueous solutions onto a hydrophilic quartz slide. This polyion cushion was held together by the electrostatic attraction between CS and PTAA. The growing process was monitored by fluorescence spectroscopy. OPH was then adsorbed onto the five-bilayer CS/PTAA system. This five-bilayer macromolecular structure compared to the solid substrate rendered stability to the enzyme by giving functional integrity in addition to the ability to react with paraoxon solutions. The ultimate goal is to use such a system to detect the presence of organophosphorus compounds with speed and sensitivity using the absorption and fluorescence detection methodologies.

A polyelectrolyte architecture was fabricated that was composed of chitosan and organophosphorus hydrolase polycations along with thioglycolic acid-capped CdSe quantum dots (QDs) as the polyanion. This film was imaged by epifluorescence microscopy. UV−vis and emission spectroscopies were used to monitor the growth of the bilayer film due to the enhanced optical property of QDs. Photoluminescence of the functionalized QDs improved when sandwiched between the polycations layers. The presence of organophosphorus compounds was confirmed through photoluminescence spectroscopy.