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At least 307 records · Page 17Linked to original sources
PubMed2005

Direct mediatorless electron transport between the monolayer of photosystem II and poly(mercapto-p-benzoquinone) modified gold electrode--new design of biosensor for herbicide detection.

Photosystem II (PSII) modified gold electrodes have been prepared providing mediatorless electron transport on the basis of electrodeposited conductive layer poly-mercapto-p-benzoquinone (polySBQ). Such electrodes are suitable in construction of biosensors for PSII inhibiting herbicides. PolySBQ layer was synthesized on (i) screen-printed gold electrodes and (ii) gold microelctodes in an array on silicon substrate, by electrochemical-oxidation of sulpho-p-benzoquinone (SBQ) at +650 mV versus Ag/AgCl. The basic properties of polySBQ layer were characterized using linear sweep voltammetry and atomic force microscopy (AFM). The typical redox response for quinones was observed. The optimal length of the polymer providing direct electron transfer (DET) was found to be very close to 30 nm. PSII particles isolated from the thermophilic cyanobacteria Synechococcus bigranulatus were physically adsorbed on the polySBQ covered gold electrodes. The generation of photocurrent was observed at E=+250 mV (versus Ag/AgCl) without addition of any mediator. The basic properties of DET were studied. We concluded that: (i) PSII active in DET is immobilized in form of monolayer; (ii) the charge transport from PSII to gold working electrode (AuWE) is fast and dominated by the rate of the enzymatic reaction; (iii) polySBQ layer drains electrons from the Q(A) pocket of the photosystem since the electrode activity is inhibited by specific inhibitor, i.e. diuron (DCMU); (iv) the stability of the photosystem immobilized on gold electrodes by using polySBQ is comparable to the stability of PSII in solution under the same experimental conditions; (v) the inhibition of the photosystem by herbicide DCMU follows the sigmoid dependence; (vi) I(50) as well as limit of detection (LOD) show an improved sensitivity compared to other published biosensing systems using PSII as bioactive part.

Adsorption↗
PubMed2005

Biocompatible, nanogold-particle fluorescence enhancer for fluorophore mediated, optical immunosensor.

Fluorophores have been used as effective signal mediators for detecting biomarkers in biosamples. The enhancement of the fluorescence can, therefore, improve the sensitivity of fluorophore-mediated biosensors. A nanogold particle (NGP), when placed at an appropriate distance from a fluorophore, can effectively enhance the fluorescence by transferring the free electrons of the fluorophore, normally used for self-quenching, to the strong surface plasmon polariton field (SPPF) of the NGP. We found that some organic solvents can also enhance the fluorescence significantly. To maximize the fluorescence enhancement, novel, biocompatible nanogold particle reagents (NGPRs) were developed by combining NGPs and biocompatible solvents and tested. The level of enhancement by NGPRs was found to be additively contributed by two enhancers. These NGPRs were able to increase the signal of a fiber-optic biosensor as much as 10 times and accurately quantify some of the important cardiac markers at a tens of picomolar level. These novel enhancers are expected to be effective for fluorophore-mediated bioimaging as well as biosensing.

Biocompatible Materials↗
PubMed2005

Quantitative detection of doping substances by a localised surface plasmon sensor.

Within this communication, consistent evidence of a quantitative biosensing principle for steroidal residue analysis is presented. Our approach uses a simple method for the quantitative determination of an anabolic agent called stanozolol (Sz). Sz (Mw 328) is widely used in sports, horse racing and as a growth promoter in animals for human consumption. Through the use of localised surface plasmons (LSPs), sustained by three-dimensional noble metal nanostructures, we have developed a highly specific, label-less immunosensor for the detection of this small organic molecule to low levels (nM range). A main practical advantage over conventional flat extended film surface plasmon resonance (SPR) systems is the simplicity of the optical configuration, since there is no need for cumbersome total internal reflection illumination, thus making integration easier. In addition, the active area of the LSP-based sensor is smaller, decreasing the minimum detectable number of molecules involved in the binding event. Assay times are short and the set-up is comprised of relatively cheap instrumentation. Detection levels found here are comparable with SPR, even at this early stage of development and with further modifications, we envisage sensing down to pM (10(-12)) levels.

Biosensing Techniques↗
PubMed2005

Waveguide excitation fluorescence microscopy: a new tool for sensing and imaging the biointerface.

A novel biosensing and imaging technique, the waveguide excitation fluorescence microscope, has been developed for the dynamic and quantitative investigation of bio-interfacial events in situ, ranging from ligand-receptor binding to focal adhesion formation in cell-surface interactions. The technique makes use of the evanescent field created when light travels in a mono-mode, planar optical waveguide to excite fluorescence in the near interface region. Advantages of the technique include high target sensitivity for fluorescence detection (femtomolar range), high surface specificity (ca. 100 nm perpendicular to the waveguide), large area analysis with submicron resolution, 'built-in' calibration of fluorescent light gain, and the capability to perform multi-colour imaging in situ and in real time. In this work, the sensitivity of the system has already been demonstrated through dynamic measurements of the streptavidin-biotin binding event to below 20 pM concentrations, signal to noise comparisons with conventional fluorescence microscopy have shown more than a 10-fold improvement, and surface specificity of the technique has also been illustrated in a comparison of fibroblast focal adhesion images. Thus, this new tool can be used to illuminate processes occurring at the interface between biology and synthetic surfaces in a unique manner.

Biosensing Techniques↗
PubMed2005

Facile preparation of amperometric laccase biosensor with multifunction based on the matrix of carbon nanotubes-chitosan composite.

The carbon nanotubes-chitosan (CNTs-CS) composite provides a suitable biosensing matrix due to its good conductivity, high stability, and good biocompatibility. Enzymes can be firmly incorporated into the matrix without the aid of other cross-linking reagents. The composite is easy to form insoluble film in solution above pH 6.3. Based on this, a facilely fabricated amperometric biosensor by entrapping laccase into the CNTs-CS composite film has been developed. At pH 6.0, the fungi laccase incorporated into the composite film remains better catalytic activity than that dissolved in solution. The system is in favor of the accessibility of substrate to the active site of laccase, thus the affinity to substrates is improved greatly, such as 2,2'-azino-bis-(3-ethylbenzthiazoline-6-sulfonic acid) diammonium salt (ABTS), catechol, and O2 with Km values of 19.86 microM, 9.43 microM, and 3.22 mM, respectively. The major advantages of the as-prepared biosensor are: detecting different substrates (ABTS, catechol, and O2), possessing high affinity and sensitivity, durable long-term stability, and facile preparation procedure. On the other hand, the system can be applied in fabrication of biofuel cells as the cathodic catalysts based on its good electrocatalysis for oxygen reduction. It can be extended to immobilize other enzymes and biomolecules, which will greatly facilitate the development of biosensors, biofuel cells, and other bioelectrochemical devices.

Biosensing Techniques↗
PubMed2006

Homopolyvalent antibody-antigen interaction kinetic studies with use of a dual-polarization interferometric biosensor.

We used dual-polarization interferometry (DPI) to study the interaction kinetics between a 'homopolyvalent' antigen (Ag) and a monoclonal antibody (Ab). A model system, which uses a monoclonal Ab against a homopentameric Ag, C-reactive protein (CRP), is presented with principle and experiments for the study of the interactions between an Ab and an Ag that has multiple identical epitopes. This allows evaluation of the dissociation constant (K(D)) and of the binding stoichiometry by DPI based on measurements of phase changes of Ab-Ag complexes in the transverse magnetic (TM) and transverse electric (TE) polarization modes. The average experimental value of K(D) found by the DPI technique for anti-CRP Ab was shown to be in close agreement with the value obtained by an indirect competition-enzyme-linked immunosorbent assay (ELISA). Moreover, the total number of Ab combining sites on the DPI sensor chip was calculated, and the binding stoichiometry of the surface Ag-Ab complex was obtained. This study illustrates the advantages of the DPI method in biosensing in its capacity for simultaneous evaluation of the thickness and refractive index (density, mass) of adsorbed layers. This allowed a comprehensive analysis of affinity reactions between an Ab having two binding sites and a multi-sited Ag.

Antibodies, Monoclonal↗
PubMed2006

Amperometric glucose biosensor based on layer-by-layer assembly of multilayer films composed of chitosan, gold nanoparticles and glucose oxidase modified Pt electrode.

A new strategy for fabricating glucose biosensor was presented by layer-by-layer assembled chitosan (CS)/gold nanoparticles (GNp)/glucose oxidase (GOD) multilayer films modified Pt electrode. First, a cleaned Pt electrode was immersed in poly(allylamine) (PAA), and then transferred to GNp, followed by the adsorption of GOD (GOD/GNp/PAA/Pt). Second, the GOD/GNp/PAA/Pt electrode was immersed in CS, and then transferred to GNp, followed by the adsorption of GOD (GOD/GNp/CS/GOD/GNp/PAA/Pt). Third, different layers of multilayer films modified Pt electrodes were assembled by repeating the second process. Film assembling and characterization were studied by quart crystal microbalance, and properties of the resulting glucose biosensors were measured by electrochemical measurements. The results confirmed that the assembling process of multilayer films was simple to operate, the immobilized GOD displayed an excellent catalytic property to glucose, and GNp in the biosensing interface efficiently improved the electron transfer between analyte and electrode surface. The amperometric response of the biosensors uniformly increased from one to six layers of multilayer films, and then reached saturation after the seven layers. Among the resulting biosensors, the biosensor based on the six layers of multilayer films was best. It showed a wide linear range of 0.5-16 mM, with a detection limit of 7.0 microM estimated at a signal-to-noise ratio of 3, fast response time (within 8s). Moreover, it exhibited good reproducibility, long-term stability and interference free. This method can be used for constructing other thin films, which is a universal immobilization method for biosensor fabrication.

Biosensing Techniques↗
PubMed2006

Screen-printed biosensors for glucose determination in grape juice.

An approach to the glucose determination by amperometric biosensing in wine industry applications is presented. Integrated screen-printed biosensors based on horseradish peroxidase (HRP) and glucose oxidase (GOx) have been developed. The experimental design methodology has been used to find the optimum conditions of the experimental variables, in such a way that a chronoamperometric response specific for glucose was recorded. Under these conditions, repeatability and reproducibility of the modified electrodes have been analyzed. The detection limit for glucose has been calculated taking into account the probability of false positive (alpha) and negative (beta), reaching a medium value of 4.37+/-0.21 micromol dm-3 (alpha=beta=0.05, and a replicate n=4). The biosensor was applied to the determination of glucose in white wine samples.

Beverages↗
PubMed2006

QCM detection of DNA targets with single-base mutation based on DNA ligase reaction and biocatalyzed deposition amplification.

A novel biosensing technique for highly specific identification of gene with single-base mutation is proposed based on the implementation of the DNA ligase reaction and the biocatalyzed deposition of an insoluble product. The target gene mediated deposition of an insoluble precipitate is then transduced by quartz crystal microbalance (QCM) measurements. In this method, the DNA target hybridizes with a capture DNA probe tethered onto the gold electrode and then with a biotinylated allele-specific detection DNA. A ligase reaction is performed to generate the ligation between the capture and the detection probes, provided there is perfect match between the DNA target and the detection probe. Otherwise even when there is an allele mismatch between them, no ligation would take place. After thermal treatment at an elevated temperature, the formed duplex melts apart that merely allows the detection probe perfectly matched with the target to remain on the electrode surface. The presence of the biotinylated allele-matched probe is then detected by the QCM via the binding to streptavidin-peroxide horseradish (SA-HRP), which catalyzes the oxidative precipitation of 3,3-diaminobenzidine (DAB) by H2O2 on the electrode and provides an amplified frequency response. The proposed approach has been successfully implemented for the identification of single-base mutation in -28 site of the beta-thalassemia gene with a detection limit of 0.1 nM, demonstrating that this method provides a highly specific and cost-efficient approach for point mutation detection.

Biosensing Techniques↗
PubMed2006

In situ DNA amplification with magnetic primers for the electrochemical detection of food pathogens.

A sensitive and selective genomagnetic assay for the electrochemical detection of food pathogens based on in situ DNA amplification with magnetic primers has been designed. The performance of the genomagnetic assay was firstly demonstrated for a DNA synthetic target by its double-hybridization with both a digoxigenin probe and a biotinylated capture probe, and further binding to streptavidin-modified magnetic beads. The DNA sandwiched target bound on the magnetic beads is then separated by using a magneto electrode based on graphite-epoxy composite. The electrochemical detection is finally achieved by an enzyme marker, anti-digoxigenin horseradish peroxidase (HRP). The novel strategy was used for the rapid and sensitive detection of polymerase chain reaction (PCR) amplified samples. Promising resultants were also achieved for the DNA amplification directly performed on magnetic beads by using a novel magnetic primer, i.e., the up PCR primer bound to magnetic beads. Moreover, the magneto DNA biosensing assay was able to detect changes at single nucleotide polymorphism (SNP) level, when stringent hybridization conditions were used. The reliability of the assay was tested for Salmonella spp., the most important pathogen affecting food safety.

Biosensing Techniques↗
PubMed2006

A highly sensitive system for urea detection by using CdSe/ZnS core-shell quantum dots.

An original and novel assay system with urease as a catalyst and CdSe/ZnS quantum dots (QDs) as an indicator has been developed for quantitative analysis of urea. By mixing urease and QDs, the determination of urea can be performed in a quantitative manner. The detection is based on the enhancement of QD photoluminescence (PL) intensity, which is correlated to the enzymatic degradation of urea. By controlling the buffer concentration and pH, PL enhancement due to the degradation of urea is linear in the urea concentration ranging from 0.01 to 100mM. This property makes the urease/QDs system to be a promising urea-biosensing system. The newly developed system is a superior design and possesses many advantages, including its simple preparation, low cost, no enzyme immobilization required, high flexibility, and good sensitivity.

Biosensing Techniques↗
PubMed2006

Convective flow effects on DNA biosensors.

We explore theoretic limits of convective flux effects, as a function of species concentrations and sample volume, in biosensing systems containing target species with differing affinities. A finite element method is used to simulate mass transport of DNA through a microfluidic chamber to the sensing surface where hybridization of DNA is modeled using the corresponding kinetic equations. Our results show enhancements due to convection are controlled by the concentration and sample volume of the lower affinity species, while the upper-limit of the enhancements are determined by the concentration and sample volume of the higher affinity species. Additionally, enhancements are controlled by the degree of competition between the two species, which is related to the total fraction of binding sites used.

Biosensing Techniques↗
PubMed2006

A novel wireless glucose sensor employing direct electron transfer principle based enzyme fuel cell.

In this paper we present a novel wireless glucose biosensing system employing direct electron transfer principle based enzyme fuel cell. Using the glucose dehydrogenase complex, which is composed of a catalytic subunit containing FAD, the cytochrome c subunit that harbors heme c as the electron transfer subunit, and chaperone-like subunit, a direct electron transfer-type glucose enzyme fuel cell was constructed. The enzyme glucose fuel cell generated electric power, and the open-circuit voltage showed glucose concentration dependence, which suggests potential applications for this glucose-sensing system. We constructed a miniaturized "all-in-one" glucose enzyme fuel cell, which represents a compartmentless fuel that is based on the direct electron transfer principle. This involved the combination of a wireless transmitter system and a simple and miniaturized continuous glucose monitoring system, which operated continuously for about 3 days with stable response. This is the first demonstration of an enzyme-based direct electron transfer-type enzyme fuel cell and fuel cell-type glucose sensor which can be utilized as a subcutaneously implantable system for continuous glucose monitoring.

Animals↗
PubMed2026

Engineering bubble structures as Cas12a activators for highly sensitive monitoring of WRN helicase function.

The Werner syndrome helicase (WRN) is a critical synthetic lethal target in microsatellite instability cancers, essential for resolving complex genomic structures like replication bubbles and R-loops. However, strategies to simultaneously discriminate WRN activity on DNA versus DNA-RNA substrates in living cells are lacking. Here, we developed a structure-specific CRISPR/Cas12a biosensing strategy to visualize WRN functional activity by engineering bubble-structure probes. These probes were rationally designed to structurally mimic DNA replication bubbles and R-loop associated DNA-RNA hybrids. Upon specific unwinding by WRN, the probes release a sequestered activator strand that triggers Cas12a trans-cleavage, effectively converting the unwinding event into an amplified fluorescent signal. This assay achieves low picomolar sensitivity (LODs: 5.6-6.0 pM) and exceptional selectivity against homologous RecQ helicases. Uniquely, this strategy enables the parallel quantification of WRN activity on both substrate types, providing insights into distinct WRN-mediated pathways for resolving genomic stress. We further demonstrated the strategy's utility by visualizing endogenous WRN dynamics in living cells and profiling the efficacy of small-molecule inhibitors. This work offers a powerful molecular toolkit for dissecting WRN biology and facilitating high-throughput drug screening in targeted cancer therapy.

Werner Syndrome Helicase↗
PubMed2006

Nanoscale controlled self-assembled monolayers and quantum dots.

Self-assembled monolayer (SAM) and fluorescent quantum dots (QDs) share common ground as emerging tools for nanoscale observation of biological interactions. SAMs provide excellent means of controlling the surface characteristics through individually tailored and engineered building blocks. SAMs on various surfaces have demonstrated clear advantages over uncontrolled multilayer films in fabricating electrochemical sensor, optical sensor, chemical biosensor, and atomic force microscopy. Similarly, QDs have advantages over organic fluorophores in long-term and real-time optical imaging of biological specimens. QDs conjugated with various biomolecules have been successfully applied to bioimaging, biosensing and cell encoding.

Animals↗
PubMed2004

Ribozyme diagnostics comes of age.

Biosensing ribozymes could soon be used to diagnose viral infection. The Kossen group from Sirna Therapeutics have developed a sensitive, high-throughput means of screening for hepatitis C virus, using their target activated half-ribozyme technology, as reported in the June issue of Chemistry & Biology.

Biosensing Techniques↗
PubMed2006

The protein-nanomaterial interface.

Developments in the past few years have illustrated the potentially revolutionizing impact of nanomaterials, especially in biomedical imaging, drug delivery, biosensing and the design of functional nanocomposites. Methods to effectively interface proteins with nanomaterials for realizing these applications continue to evolve. Proteins are being used to control both the synthesis and assembly of nanomaterials. There has also been an increasing interest in understanding the influence of nanomaterials on the structure and function of proteins. Understanding and controlling the protein-nanomaterial interface will be crucial for designing functional protein-nanomaterial conjugates and assemblies.

Binding Sites↗
PubMed2005

Novel detection system for biomolecules using nano-sized bacterial magnetic particles and magnetic force microscopy.

A system for streptavidin detection using biotin conjugated to nano-sized bacterial magnetic particles (BMPs) has been developed. BMPs, isolated from magnetic bacteria, were used as magnetic markers for magnetic force microscopy (MFM) imaging. The magnetic signal was obtained from a single particle using MFM without application of an external magnetic field. The number of biotin conjugated BMPs (biotin-BMPs) bound to streptavidin immobilized on the glass slides increased with streptavidin concentrations up to 100 pg/ml. The minimum streptavidin detection limit using this technique is 1 pg/ml, which is 100 times more sensitive than a conventional fluorescent detection system. This is the first report using single domain nano-sized magnetic particles as magnetic markers for biosensing. This assay system can be used for immunoassay and DNA detection with high sensitivities.

Bacterial Proteins↗