Nonaqueous biocatalytic degradation of a nerve gas mimic

Carbon dot composites for bioapplications: a review

Recent advancements in the synthesis of carbon dot composites and their applications in biomedical fields (bioimaging, drug delivery and biosensing) have been carefully summarized. The current challenges and future trends of CD composites in this field have also been discussed.

Construction of a luminescent sensor based on a lanthanide complex for the highly efficient detection of methyl parathion

A highly sensitive and selective luminescent sensor for the detection of methyl parathion (MP) pesticide was described in this study. The target molecule HL was synthesized by modifying the structure of 4-hydroxybenzlidene imidazolinone (HBI) with nitrogen-containing heterocyclic 1,10-phenanthroline. In the presence of Eu³⁺, a HL–Eu³⁺ complex was formed which could emit strong red fluorescence due to the removal of coordinated water molecules and an intramolecular energy transfer from HL to Eu³⁺. Addition of MP into the strongly fluorescent solution of HL–Eu³⁺ induced quenching of the complex's fluorescence, and this quenching behavior occurred because of the competition coordination of MP and HL for Eu³⁺. A calibration curve was developed that related the extent of fluorescence quenching to MP concentration, making the HL–Eu³⁺ system a sensitive and selective fluorescent sensor for MP. Under the experimental conditions, the detection limit for MP was down to 95 nM based on LOD = 3σ/S. Moreover, the fluorescence assay developed here allowed the detection of MP in two different types of real samples including pond water and pear juice, and satisfactory results demonstrate that this fluorescent sensor based on HL–Eu³⁺ has potential application in environment and food analysis.

A lanthanide complex sensor HL–Eu³⁺ based on an aromatic cyclic polyamine ligand was constructed for MP detection.

A supersensitive silver nanoprobe based aptasensor for low cost detection of malathion residues in water and food samples

In the present study, we report a highly sensitive, rapid and low cost colorimetric monitoring of malathion (an organophosphate insecticide) employing a basic hexapeptide, malathion specific aptamer (oligonucleotide) and silver nanoparticles (AgNPs) as a nanoprobe. AgNPs are made to interact with the aptamer and peptide to give different optical responses depending upon the presence or absence of malathion. The nanoparticles remain yellow in color in the absence of malathion owing to the binding of aptamer with peptide which otherwise tends to aggregate the particles because of charge based interactions. In the presence of malathion, the agglomeration of the particles occurs which turns the solution orange. Furthermore, the developed aptasensor was successfully applied to detect malathion in various water samples and apple. The detection offered high recoveries in the range of 89-120% with the relative standard deviation within 2.98-4.78%. The proposed methodology exhibited excellent selectivity and a very low limit of detection i.e. 0.5pM was achieved. The developed facile, rapid and low cost silver nanoprobe based on aptamer and peptide proved to be potentially applicable for highly selective and sensitive colorimetric sensing of trace levels of malathion in complex environmental samples.

Facile colorimetric detection of 6-benzylaminopurine based on p-aminobenzenethiol functionalized silver nanoparticles

A simple colorimetric assay has been developed to detect 6-benzylaminopurine (6-BA) in a complex environment by using the novel probe p-aminobenzenethiol functionalized silver nanoparticles (ABT-AgNPs).

Lab-on-a-drop: biocompatible fluorescent nanoprobes of gold nanoclusters for label-free evaluation of phosphorylation-induced inhibition of acetylcholinesterase activity towards the ultrasensitive detection of pesticide residues

The catalysis and phosphorylated inhibition of acetylcholinesterase were monitored using fluorescent AuNCs nanoprobes for detecting pesticide residues.

Removal of methyl parathion from artificial off-gas using a bioreactor containing a constructed microbial consortium

Methyl parathion (MP), a highly toxic organophosphorus pesticide, was widely used for agriculture crop protection. During the production of MP and the process of MP-containing wastewater treatment, MP can release into the atmosphere and will do great harm to adjacent communities. A consortium comprised of an engineered microorganism and a natural p-nitrophenol (PNP) degrader was assembled for complete mineralization of MP. We genetically engineered Escherichia coli BL21 (DE3) enabling the overexpression of methyl parathion hydrolase (MPH). In addition, we isolated Ochrobactrum sp. strain LL-1 that utilized PNP, a product of MP hydrolysis, as the sole carbon, nitrogen, and energy source. The coculture effectively hydrolyzed 0.2 mM MP and prevented the accumulation of PNP in suspended culture. A laboratory-scale bioreactor containing the dual-species consortium was developed for the treatment of artificial off-gas containing MP. The bioreactor maintained over 98% of average MP removal efficiency over a 75 day period, and PNP produced from hydrolysis of MP was degraded completely, indicating that complete mineralization of MP was achieved. The strategy of linking degrading consortium to a bioreactor may provide an alternative to physicochemical abatement technologies for the treatment of waste-gas streams containing MP as well as other PNP-substituted organophosphates.

(CdSe)ZnS Quantum Dots and Organophosphorus Hydrolase Bioconjugate as Biosensors for Detection of Paraoxon

In this paper, we first report a novel biosensor for the detection of paraoxon based on (CdSe)ZnS core-shell quantum dots (QDs) and an organophosphorus hydrolase (OPH) bioconjugate. The OPH was coupled to (CdSe)ZnS core-shell QDs through electrostatic interaction between negatively charged QDs surfaces and the positively charged protein side chain and ending groups (-NH2). Circular dichroism (CD) spectroscopy showed no significant change in the secondary structure of OPH after the bioconjugation, which indicates that the activity of OPH was preserved. Detectable secondary structure changes were observed by CD spectroscopy when the OPH/QDs bioconjugate was exposed to organophosphorus compounds such as paraoxon. Photoluminescence (PL) spectroscopic study showed that the PL intensity of the OPH/QDs bioconjugate was quenched in the presence of paraoxon. The overall quenching percentage as a function of paraoxon concentration matched very well with the Michaelis-Menten equation. This result indicated that the quenching of PL intensity was caused by the conformational change in the enzyme, which is confirmed by CD measurements. The detection limit of paraoxon concentration using OPH/QDs bioconjugate was about 10(-8) M. Although increasing the OPH molar ratio in the bioconjugates will slightly increase the sensitivity of biosensor, no further increase of sensitivity was achieved when the molar ratio of OPH to QDs was greater than 20 because the surface of QDs was saturated by OPH. These properties make the OPH/QDs bioconjugate a promising biosensor for the detection of organophosphorus compounds.

Biomaterials for mediation of chemical and biological warfare agents

Recent events have emphasized the threat from chemical and biological warfare agents. Within the efforts to counter this threat, the biocatalytic destruction and sensing of chemical and biological weapons has become an important area of focus. The specificity and high catalytic rates of biological catalysts make them appropriate for decommissioning nerve agent stockpiles, counteracting nerve agent attacks, and remediation of organophosphate spills. A number of materials have been prepared containing enzymes for the destruction of and protection against organophosphate nerve agents and biological warfare agents. This review discusses the major chemical and biological warfare agents, decontamination methods, and biomaterials that have potential for the preparation of decontamination wipes, gas filters, column packings, protective wear, and self-decontaminating paints and coatings.

Water plays a different role on activation thermodynamic parameters of alcoholysis reaction catalyzed by lipase in gaseous and organic media

The effect of water on the alcoholysis of methyl propionate and n-propanol catalyzed by immobilized Candida antarctica lipase B (CALB) has been compared in a continuous solid-gas reactor and in an organic liquid medium. The enthalpic and entropic contributions of water to the Gibbs free energy of activation in the gas phase were different from the ones in the organic phase, the inverse trends being observed for the variation of both DeltaH* and DeltaS* with water activity. Different phenomena were identified for their influence on the thermodynamic parameters. When increasing a(w), the enhanced flexibility of the enzyme was predominant in the gas phase whereas substrate-solvent interactions due to an increased polarity of the solvent affected mainly the thermodynamic parameters in the organic phase. The observed variations of DeltaG* with water activity were in accordance with kinetics results previously obtained in both reaction media.

Direct transesterification of gases by "dry" immobilized lipase

Several different reactor configurations, including single pass, continuous recycle, and batch reactor modes, were used to investigate the effects of temperature and water activity, or relative humidity, on lipase-catalyzed, gas-phase transesterifications. Temperature and relative humidity were controlled both inside reactors and throughout the course of the reaction to account for and optimize their effects. Results indicated that, at low relative humidity, reaction rates increased with temperature up to 60 degrees C. However, when relative humidity was increased, a similar increase in temperature resulted in the loss of nearly all enzyme activity. These results are consistent with the idea that enzymes without free water are more thermally stable. Furthermore, at constant ambient temperatures, production increased dramatically with an increase in relative humidity, confirming the idea that an increase in water activity increases catalytic activity. A mass balance performed on reactors at higher relative humidity revealed that hydrolysis (rather than transesterification) of the ester substrate could significantly decrease product yields.

Degradation of organophosphorous nerve agents by enzyme-polymer nanocomposites: efficient biocatalytic materials for personal protection and large-scale detoxification

The biocatalytic destruction of organophosphates has become an important focus area, as efficient "clean" technologies are sought for chemical weapons decommissioning, counteracting nerve agent attacks, and protecting against organophosphate pesticide poisoning. A novel method is advanced for immobilizing the broad-spectrum enzyme organophosphorous hydrolase (OPH) from Pseudomonas diminuta, based on the formation of nanocomposite protein-silicone polymers. The resulting materials are highly active, stable, and versatile biocatalysts for the liquid and gas phase detoxification of organophosphates, and can be fabricated as monoliths, sheets, thick films, granulates, or macroporous foams. This approach offers an efficient avenue to robust, high-performance biocatalytic OPH-containing polymers that outperform immobilized OPH catalysts reported to date. The method provides for the first time a route to biocatalytic materials that may be suitable for "active" protective wear, as well as bulk catalysts for the destruction of large volumes of organophosphates. The preparation of OPH-silicone biocomposites, their performances in the liquid and gas phase detoxification of paraoxon, dichlorvos, and diisopropyl fluorophosphate, and their features are discussed.

Bioencapsulation within synthetic polymers (Part 2): non-sol-gel protein-polymer biocomposites

Since the introduction of sol-gel bioencapsulation and the demonstration that biological function can be incorporated into, and preserved within, polymer matrices, a number of alternative polymers have been used to immobilize proteins. Various enzymes have been trapped in such diverse polymers as epoxy-amine resins, polyvinyl plastics, polyurethane foams and silicone elastomers. Together with sol-gel encapsulates, these biocomposites represent a powerful approach for immobilizing biological materials for applications as biosensors and biocatalysts, and hold promise as bioactive, fouling-resistant polymers for environmental, food and medical uses. Although still at the developmental stage, these biocomposites promise to revolutionize the whole arena of high-performance bioimmobilization.

Increasing the tolerance of organophosphorus hydrolase to bleach

Organophosphorus hydrolase (OPH) has been incorporated within polyurethane foams during polymer synthesis as a means of reducing the enzyme's environmental sensitivity to alterations in pH and bleach-induced enzyme denaturation. Unfavorable losses of enzyme activity upon altered pH are reduced by covalently incorporating OPH within polyurethane matrices. Also, the stability of the immobilized enzyme under alkaline conditions is significantly enhanced. The bleach compatibility of OPH is also increased upon enzyme polymerization. Although a fraction of the increased bleach compatibility results from polyurethane oxidation, the covalent linkages between OPH and polyurethane directly enhance enzyme stability in buffered solutions of calcium hypochlorite bleach. Copyright 1999 John Wiley & Sons, Inc.

Rational design of organophosphorus hydrolase for altered substrate specificities

Organophosphorus hydrolase (OPH) is a bacterial enzyme that hydrolyzes a broad variety of OP neurotoxins, including chemical warfare agents and many widely used pesticides. OPH has extremely high hydrolytic efficiency with different phosphotriester and phophothiolester pesticides (k(cat) = 50-15,000 s(-1)) as well as phosphorofluorates such as DFP and the chemical warfare agents sarin and soman (k(cat) = 50-11,000 s(-1)). In contrast, the enzyme has much lower catalytic capabilities for phosphonothioate neurotoxins such as acephate or the chemical warfare agent VX [O-ethyl S-(2-diisopropyl aminoethyl) methylphosphonothioate] (k(cat) = 0.3-20 s(-1)). Different metal-associated forms of the enzyme have demonstrated varying hydrolytic capabilities for each of the OP neurotoxins, and the activity of OPH (Co2+) is consistently higher than that of OPH (Zn2+) by five- to 20-fold. Protein engineering strategies have exploited these metal-induced catalytic differences, and other slight modifications to the opd gene have resulted in significant enhancement of the rates of detoxification of the thioate pesticides and chemical warfare agents. In order to develop practical applications of OPH, other experiments have focused on improvement of enzyme production, localization, stability, and shelf-life, as well as efficient catalysis of substrates of interest.