GDH biosensor based off-line capillary immunoassay for alkylphenols and their ethoxylates

PQQ-GDH - Structure, function and application in bioelectrochemistry

This review summarizes the basic features of the PQQ-GDH enzyme as one of the sugar converting biocatalysts. Focus is on the membrane -bound and the soluble form. Furthermore, the main principles of enzymatic catalysis as well as studies on the physiological importance are reviewed. A short overview is given on developments in protein engineering. The major part, however, deals with the different fields of application in bioelectrochemistry. This includes approaches for enzyme-electrode communication such as direct electron transfer, mediator-based systems, redox polymers or conducting polymers and holoenzyme reconstitution, and covers applied areas such as biosensing, biofuel cells, recycling schemes, enzyme competition, light-directed sensing, switchable detection schemes, logical operations by enzyme electrodes and immune sensing.

An enzyme-modified capillary as a platform for simultaneous fluorometric detection of d-glucose and l- lactate

The preparation of a glass capillary pattered with lipid layers　on which lactate dehydrogenase (LDH) and glucose dehydrogenase (GDH) were regionally adsorbed and its application for simultaneous detection of d-glucose and l-lactate in human serum is described. A lipid layer was formed on the surface of BSA-unabsorbed octadecyltrichlorosilane (OTS) inner wall of a glass capillary. The electrostatic charge of the lipid layer was a key factor for adsorbing the enzymes on the lipid layer. The fluorescence intensities were observed at each enzyme site in the presence of diaphorase (DIA), β-nicotinamide-adenine dinucleotide oxidized (NAD), resazurin, d-glucose and l-lactate. The fluorescence intensities at each enzyme site increased with an increase in the concentration of d-glucose and l-lactate=with the detection limits of 32 μM and 4.9 μM, respectively.

Prediction of wastewater quality using amperometric bioelectronic tongues

Wastewater samples from a Swedish chemi-thermo-mechanical pulp (CTMP) mill collected at different purification stages in a wastewater treatment plant (WWTP) were analyzed with an amperometric enzyme-based biosensor array in a flow-injection system. In order to resolve the complex composition of the wastewater, the array consists of several sensing elements which yield a multidimensional response. We used principal component analysis (PCA) to decompose the array's responses, and found that wastewater with different degrees of pollution can be differentiated. With the help of partial least squares regression (PLS-R), we could link the sensor responses to the Microtox® toxicity parameter, as well as to global organic pollution parameters (COD, BOD, and TOC). From investigating the influences of individual sensors in the array, it was found that the best models were in most cases obtained when all sensors in the array were included in the PLS-R model. We find that fast simultaneous determination of several global environmental parameters characterizing wastewaters is possible with this kind of biosensor array, in particular because of the link between the sensor responses and the biological effect onto the ecosystem into which the wastewater would be released. In conjunction with multivariate data analysis tools, there is strong potential to reduce the total time until a result is yielded from days to a few minutes.

Theory and practice of enzyme bioaffinity electrodes. Chemical, enzymatic, and electrochemical amplification of in situ product detection

The two articles in this series are dedicated to bioaffinity electrodes with in situ detection of the product of the enzyme label after recognition by its conjugate immobilized on the electrode. Part 1 was devoted to direct electrochemical detection, whereas the present contribution deals with homogeneous chemical and enzymatic amplification of the primary electrochemical signal. The theoretical relationships that are established for these modes of amplification are applied to the avidin-biotin recognition in a system that involves alkaline phosphatase as enzyme label and 4-amino-2,6-dichloro-phenyl phosphate as substrate, generating 2,6-dichloro-4-aminophenol as electrochemically active product. Chemical amplification then results from the addition of NADH, which reduces the 2,6-dichloro-quinonimine resulting from the electrochemical oxidation of 2,6-dichloro-4-aminophenol. An increased amplification is obtained when the reduction of 2,6-dichloro-quinonimine involves diaphorase in solution with NADH as substrate. The excellent agreement between theoretical predictions and experimental data required a detailed theoretical analysis and the independent determination of the key kinetic parameters of the system. The theoretical analysis was extended to monolayer and multilayered films of auxiliary enzyme as well as to electrochemical amplification by means of closely spaced dual electrodes so as to offer a rational comparative panorama of the amplification capabilities of the various possible strategies. Confinement of the profile of the product, and/or its oxidized form, in the vicinity the electrode surface appears as a key parameter of amplification.

Specific binding of large aggregates of amphiphilic molecules to the respective antibodies

The Binding of nonylphenol to respective antibodies immobilized on solid substrates was studied with the methods of total internal reflection ellipsometry (TIRE) and QCM (quartz crystal microbalance) impedance spectroscopy. The binding reaction was proved to be highly specific having an association constant of KA=1.6x10(6) mol(-1) L and resulted in an increase in both the adsorbed layer thickness of 23 nm and the added mass of 18.3 microg/cm2 at saturation. The obtained responses of both TIRE and QCM methods are substantially higher than anticipated for the immune binding of single molecules of nonylphenol. The mechanism of binding of large aggregates of nonylphenol was suggested instead. Modeling of the micelle of amphiphilic nonylphenol molecules in aqueous solutions yielded a micelle size of about 38 nm. The mechanism of binding of large molecular aggregates to respective antibodies can be extended to other hydrophobic low-molecular-weight toxins such as T-2 mycotoxin. The formation of large molecular aggregates of nonylphenol and T-2 mycotoxin molecules on the surface was proved by the AFM study.

Advantages and limitations of on-line solid phase extraction coupled to liquid chromatography–mass spectrometry technologies versus biosensors for monitoring of emerging contaminants in water

On-line solid phase extraction (SPE) coupled to liquid chromatography-mass spectrometry (LC-MS) and biosensors are advanced technologies that have found increasing application in the analysis of environmental contaminants although their application to the determination of emerging contaminants (previously unknown or unrecognized pollutants) has been still limited. This review covers the most recent advances occurred in the areas of on-line SPE-LC-MS and biosensors, discusses and compares the main strengths and limitations of the two approaches, and examines their most relevant applications to the analysis of emerging contaminants in environmental waters. So far, the on-line configuration most frequently used has been SPE coupled to liquid chromatography-(tandem) mass spectrometry. Sorbents used for on-line SPE have included both traditional (alkyl-bonded silicas and polymers) and novel (restricted access materials (RAMs), molecularly imprinted synthetic polymers (MIPs), and immobilized receptors or antibodies (immunosorbents) materials. The biosensor technologies most frequently applied have been based on the use of antibodies and, to a lesser extent, enzymes, bacteria, receptors and DNA as recognition elements, and the use of optical and electrochemical transducing elements. Emerging contaminants investigated by means of these two techniques have included pharmaceuticals, endocrine disrupting compounds such as estrogens, alkylphenols and bisphenol A, pesticides transformation products, disinfection by-products, and bacterial toxins and mycotoxins, among others. Both techniques offer advantageous, and frequently comparable, features such as high sensitivity and selectivity, minimum sample manipulation, and automation. Biosensors are, in addition, relatively cheap and fast, which make them ideally suited for routine testing and screening of samples; however, in most cases, they can not compete yet with on-line SPE procedures in terms of accuracy, reproducibility, reliability (confirmation) of results, and capacity for multi-analyte determination.

Biosensors as useful tools for environmental analysis and monitoring

Recent advances in the development and application of biosensors for environmental analysis and monitoring are reviewed in this article. Several examples of biosensors developed for relevant environmental pollutants and parameters are briefly overviewed. Special attention is paid to the application of biosensors to real environmental samples, taking into consideration aspects such as sample pretreatment, matrix effects and validation of biosensor measurements. Current trends in biosensor development are also considered and commented on in this work. In this context, nanotechnology, miniaturisation, multi-sensor array development and, especially, biotechnology arise as fast-growing areas that will have a marked influence on the development of new biosensing strategies in the near future.

Analysis of nonylphenol: advances and improvements in the immunochemical determination using antibodies raised against the technical mixture and hydrophilic immunoreagents

The development of an enzyme-linked immunosorbent assay (ELISA) for the detection of technical nonylphenol (NP) is reported. The preparation of specific antibodies has been addressed using an immunizing hapten with a four-carbon atom spacer arm placed at the ortho position that preserves both the hydroxyl group and the complexity of the branched nonyl chain mixture of the technical NP. The synthesis of the immunizing hapten 5-(2-hydroxy-5-nonylphenyl)-pentanoic acid has been accomplished through a four-step synthetic pathway using the NP commercial technical mixture as the starting material. Three types of competitor haptens have also been prepared depending on the location of the spacer arm: in ortho position to the phenol group (type A), attached to the oxygen atom (type B), and in para position, substituting the nonyl chain (type C). Drawbacks produced by the hydrophobicity of the NP or of the hapten derivatives have been circumvented by using a highly hydrophilic carrier molecule such as a high-molecular-weight aminodextran as a coating support for antigen in an indirect ELISA format. A reproducible and sensitive indirect competitive ELISA has been finally obtained, reaching a limit of detection of 2.3 +/- 0.9 microg L(-1) and an IC50 value of 29 +/- 5 microg L(-1) (both N = 16). A coefficient of variation of 11% for assays performed on different days (N = 5; IC50 = 30 +/- 3 microg L(-1)) demonstrates the assay reproducibility. The assay also recognizes the nonylphenol polyethoxylates to a different degree depending on the length of the ethoxylate chain. Recovery values in the range between 96 and 100% have been obtained using spiked blind aqueous samples although the sample preparation procedure used has been shown to have a great influence on the method accuracy. A preliminary evaluation of the analytical protocol established has been performed using real water samples.

Engineering PQQ glucose dehydrogenase with improved substrate specificity

Site-directed mutagenesis was carried out on the active site of water-soluble PQQ glucose dehydrogenase (PQQGDH-B) to improve its substrate specificity. Amino acid substitution of His168 resulted in a drastic decrease in the enzyme's catalytic activity, consistent with its putative catalytic role. Substitutions were also carried out in neighboring residues, Lys166, Asp167, and Gln169, in an attempt to alter the enzyme's substrate binding site. Lys166 and Gln169 mutants showed only minor changes in substrate specificity profiles. In sharp contrast, mutants of Asp167 showed considerably altered specificity profiles. Of the numerous Asp167 mutants characterized, Asp167Glu showed the best substrate specificity profile, while retaining most of its catalytic activity for glucose and stability. We also investigated the cumulative effect of combining the Asp167Glu substitution with the previously reported Asn452Thr mutation. Interpretation of the effect of the replacement of Asp167 to Glu on the alteration of substrate specificity in relation with the predicted 3D model of PQQGDH-B is also discussed.