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At least 721 records · Page 40Linked to original sources
PubMed2006

Fabrication of a planar-form screen-printed solid electrolyte modified Ag/AgCl reference electrode for application in a potentiometric biosensor.

This study features the fabrication of a planar-form, solid electrolyte modified, (PSEM) Ag/AgCl reference electrode using a screen-printing method. The PSEM Ag/AgCl reference electrode uses agar gel as the inner electrolyte and chloroprene rubber for the liquid junction and insulator. These common low-cost materials and the simple fabrication processes involved render the proposed reference electrode an ideal candidate for cost-efficient mass production. It is shown that the developed reference electrode is insensitive to most of the physiologically important ionic species, including Na+, K+, Li+, Ca2+, NH4+, and Cl-, under continuous measurement conditions. Moreover, as with conventional commercial reference electrodes, the proposed reference electrode exhibits a reversible response, which is maintained until the agar gel dries out. The PSEM Ag/AgCl reference electrode is integrated with an iridium oxide modified Pt-based pH indicator electrode to form a chip-type pH biosensor. The performance of this biosensor is consistent with that obtained from a pH meter based on a macroscopic commercial Ag/AgCl reference electrode. The experimental results confirm that the proposed biosensor is capable of providing precise pH measurements of various real samples. Accordingly, the PSEM Ag/AgCl reference electrode presented in this study provides a viable alternative to the macroscopic Ag/AgCl reference electrode used in many conventional chip-based pH sensors.

Biosensing Techniques↗
PubMed2006

DNA-directed protein immobilization for simultaneous detection of multiple analytes by surface plasmon resonance biosensor.

A versatile multichannel biosensor surface is prepared by site-directed immobilization of single-stranded DNA-protein conjugates onto a patterned self-assembled monolayer composed of ssDNA thiols and oligo(ethylene glycol)-terminated thiols. The conjugates each consist of an antibody chemically linked to a unique ssDNA target with a sequence complementary to the surface-bound ssDNA probes and are immobilized on the surface via sequence-specific hybridization. The exceptional specificity of DNA hybridization combined with the diversity of available sequences makes this platform perfect for multichannel sensors. Once the surface is patterned with the appropriate probe sequences, sequence-specific hybridization sorts out the target conjugates and directs them to the appropriate spots on the surface. Previously (Boozer, C. L.; Ladd, J.; Chen, S.; Yu, Q.; Homola, J.; Jiang, S. Anal. Chem. 2004, 76, 6967-6972), we performed proof-of-concept experiments demonstrating the feasibililty of using DNA-directed protein immobilization to produce a single channel biosensor. In this work, we extend this technique and employ DNA-directed protein immobilization to functionalize a multichannel biosensor, which was used for the simultaneous detection of a set of three fertility hormones: human chorionic gonadotropin, human luteinizing hormone, and follicle stimulating hormone by surface plasmon resonance sensor.

Antibodies↗
PubMed2006

Carbon nanofiber-based glucose biosensor.

The use of highly activated carbon nanofibers for the design of catalytic electrochemical biosensors is demonstrated. The direct immobilization of enzymes onto the surface of carbon nanofibers is shown to be a highly efficient method for the development of a new class of very sensitive, stable, and reproducible electrochemical biosensors. These results establish the fact that the carbon nanofiber is the best matrix so far described for the development of biosensors, far superior to carbon nanotubes or graphite powder.

Biosensing Techniques↗
PubMed2007

Label-free protein biosensor based on aptamer-modified carbon nanotube field-effect transistors.

We have fabricated label-free protein biosensors based on aptamer-modified carbon nanotube field-effect transistors (CNT-FETs) for the detection of immunoglobulin E (IgE). After the covalent immobilization of 5'-amino-modified 45-mer aptamers on the CNT channels, the electrical properties of the CNT-FETs were monitored in real time. The introduction of target IgE at various concentrations caused a sharp decrease in the source-drain current, and a gradual saturation was observed at lower concentrations. The amount of the net source-drain current before and after IgE introduction on the aptamer-modified CNT-FETs increased as a function of IgE concentration. The detection limit for IgE was determined as 250 pM. We have also prepared CNT-FET biosensors using a monoclonal antibody against IgE (IgE-mAb). The electrical properties of the aptamer- and antibody-modified CNT-FETs were compared. The performance of aptamer-modified CNT-FETs provided better results than the ones obtained using IgE-mAb-modified CNT-FETs under similar conditions. Thus, we suggest that the aptamer-modified CNT-FETs are promising candidates for the development of label-free protein biosensors.

Aptamers, Nucleotide↗
PubMed1996

Zeptomole-detecting biosensor for alkaline phosphatase in an electrochemical immunoassay for 2,4-dichlorophenoxyacetic acid.

A bienzyme substrate-recycling biosensor in a flow injection analysis system is described for the sensitive measurement of alkaline phosphatase (ALP) and applied to the fast readout of a competitive immunoassay for the widely used pesticide 2,4-dichlorophenoxyacetic acid (2,4-D). The phenol-indicating biosensor consists of a Clark-type electrode covered by a membrane with coentrapped tyrosinase and quinoprotein glucose dehydrogenase. ALP dephosphorylates phenyl phosphate to phenol (K(m) = 36 microM) outside the flow system. Phenol is oxidized in the sensor membrane by the oxygen-consuming tyrosinase via catechol to o-quinone. The quinone is reconverted to catechol by glucose dehydrogenase. This substrate cycling results in a 350-fold amplified sensor response to phenol. The oxygen consumption of the enzyme couple in the presence of phenol is monitored as a decrease in current. A total of 3.2 fM ALP (320 zmol/ 100 microL) has been detected after a 57.5 min incubation with phenyl phosphate. All involved reagents are stable over the time of measurement. The sensor does not produce any measurable blank signals. The immunoassay detects 0.1 microgram/L 2,4-D, the maximum concentration for pesticides allowed in drinking water by European Community regulations. The applicability of this biosensor for fast immunoassay readout is demonstrated by a 2 min incubation. By comparison, a standard photometric method (p-nitrophenyl phosphate) requires overnight incubation.

2,4-Dichlorophenoxyacetic Acid↗
PubMed1997

Characterization of immobilization of an enzyme in a modified Y zeolite matrix and its application to an amperometric glucose biosensor.

A new approach to construct an amperometric biosensor is described. Without using bovine serum albumin-glutaraldehyde, glucose oxidase (GOx) was immobilized on a dealuminized Y zeolite (DAY)-modified platinum electrode to construct a glucose sensor. The large specific surface area of the zeolite substrate resulted in high enzyme loading. The immobilized GOx in this manner was stable and could maintain its high activity for at least 3 months. The interactions between the zeolite and the enzyme were investigated by means of Fourier transform infrared spectra, and the pore distribution and the surface acid property of DAY were preliminarily studied. The results showed that the hydrophilic property and the existing mesopores of DAY played important roles in the enzyme immobilization. This resulting biosensor exhibited good reproducibility and selectivity, owing to the uniform pore structure and unique ion-exchange property of the zeolite. The biosensor responded rapidly to glucose in the linear range from 2.0 x 10(-6) to 3.0 x 10(-3) M, with a detection limit of 0.5 microM.

Biosensing Techniques↗
PubMed1997

Analysis of biosensor chips for identification of nucleic acids.

Two novel DNA-sequencing methods are described that use DNA hybridization biosensor chips. These two techniques involve either labeling the free nucleic acid with enriched stable isotopes or hybridizing DNA without labels to immobilized peptide nucleic acid (PNA) and detecting the phosphorus present in the DNA but not in the PNA. Sputter-initiated resonance ionization microprobe analysis was used to detect the presence of enriched tin isotope-labeled DNA and of phosphorus in natural DNA as a means to identify the presence of DNA after hybridization to oligodeoxynucleotides (ODNs) or PNAs, respectively, immobilized on a biosensor chip. The data clearly demonstrate that excellent discrimination between complementary and noncomplementary sequences can be obtained during hybridization of DNA to either ODNs or PNAs. The capability to detect different enriched stable isotope-labeled DNAs simultaneously allows high degrees of multiplexing which may be very advantageous for hybridization kinetics studies in complex systems, as well as significantly increasing the speed of analysis. Alternatively, by using natural DNA with PNA biosensor chips, discrimination for single-point mutation could be increased because of improved hybridization kinetics and direct analysis of genomic DNA may become possible without amplification. Both methods have the potential to provide a rapid method for DNA/RNA sequencing, diagnostics, and mapping.

Biosensing Techniques↗
PubMed1999

Utility of wiring nitrate reductase by alkylpyrroleviologen-based redox polymers for electrochemical biosensor and bioreactor applications.

The purpose of this work was to see if the alkylpyrroleviologen redox polymer technology previously developed for a reagentless nitrate biosensor based on nitrate reductase (NaR) from Escherichia coli (Cosnier, S.; Innocent, C.; Jouanneau, Y. Anal. Chem. 1994, 66, 3198-3201) could be applied to the isozyme from Aspergillus niger. In particular, the enzyme viability after immobilization was of great interest, as Cosnier et al. reported a residual activity of only 0.33% of the amount initially applied. The present work showed that A. niger NaR lost 99.2% of soluble activity on vacuum-drying in the presence of 2.5 nM N-methyl-N'-(12-[pyrrol-1-yl]dodecyl)-4,4'-bipyridinium ditetrafluoroborate monomer (C12V2+) and that most of this loss was due to monomer inhibition (91%). The loss due to dehydration was only 8%. In the biosensor configuration, the enzyme gave a residual activity of 0.18% of the amount originally applied and a specific response of 1.7 mA M-1 cm-2, but all activity was lost after 4 d storage at 4 degrees C in phosphate buffer. It was concluded that for practical biosensors and bioreactors, modification of the redox polymer format was needed, for example by covalent immobilization, to effect higher loading of viable NaR and improved enzyme stability.

Bioreactors↗
PubMed1999

A fiber-optic evanescent wave DNA biosensor based on novel molecular beacons.

We have prepared a novel optical fiber evanescent wave DNA biosensor using a newly developed molecular beacon DNA probe. The molecular beacons (MB) are oligonucleotide probes that become fluorescent upon hybridization with target DNA/RNA molecules. Biotinylated MBs have been designed and immobilized on an optical fiber core surface via biotin-avidin or biotin-streptavidin interactions. The DNA sensor based on a MB does not need labeled analyte or intercalation reagents. It can be used to directly detect, in real-time, target DNA/RNA molecules without using competitive assays. The sensor is rapid, stable, highly selective, and reproducible. We have studied the hybridization kinetics of the immobilized MB by changing the ionic strength of the hybridization solution and target DNA concentration. Our result shows divalent cations play a more important role than monovalent cations in stabilizing the MB stem hybrids and in accelerating the hybridization reaction with target DNA/RNA molecules. The concentration detection limit of the MB evanescent wave biosensor is 1.1 nM. The MB DNA biosensor has been applied to the analysis of specific gamma-actin mRNA sequences amplified by polymerase chain reaction.

Actins↗
PubMedDate not supplied

Synthesis and characterization of a biotin-alginate conjugate and its application in a biosensor construction.

Biotin was covalently coupled with alginate in an aqueous-phase reaction by means of carbodiimide-mediated activation chemistry to provide a biotin-alginate conjugate for subsequent use in biosensor applications. The synthetic procedure was optimized with respect to pH of the reaction medium (pH 6.0), the degree of uronic acid activation (20%), and the order of addition of the reagents. The biotin-alginate conjugate was characterized by titration with 2-anilinonaphthalene-6-sulfonic acid (2,6-ANS), 4-hydroxyazobene-2'-carboxylic acid (HABA) and by an HPSEC-MALLS analytical method as well as by FTIR and 13C NMR spectroscopy. As a compromise between the need for a high percent of molar modification of the alginate, on one hand, and sufficient gelling capability, on the other hand, an optimal modification of 10-13% of biotin-alginate was used. The new biotin-alginate conjugate was used for the encapsulation of bioluminescent reporter cells into microspheres. A biosensor was prepared by conjugating these biotinylated alginate microspheres to the surface of a streptavidin-coated optical fiber, and the performance of the biosensor was demonstrated in the determination of the antibiotic, mitomycin C as a model toxin.

Alginates↗
PubMedDate not supplied

Synthesis and characterization of a pyrrole-alginate conjugate and its application in a biosensor construction.

N-(3-Aminopropyl)pyrrole was covalently coupled with alginate in an aqueous-phase reaction by means of carbodiimide-mediated activation chemistry to provide a pyrrole-alginate conjugate for subsequent use in biosensor applications. The pyrrole-alginate conjugate was quantified by UV spectroscopy at 230 nm, by an HPSEC-MALLS analytical method, as well as by FTIR and 13C NMR spectroscopies. The new pyrrole-alginate conjugate was used for the immobilization of polyphenol oxidase (PPO) onto an electrode surface by physical entrapment resulting from the gellification process and electrochemical polymerization of the pyrrole groups. The efficiency of this cross-linking approach (chemical and electrochemical) was investigated by comparing the amount of enzyme released from polypyrrole-alginate and regular alginate. In addition, biosensors were prepared by entrapment of the PPO in polypyrrole-alginate and regular alginate matrixes and their performance for the amperometric determination of catechol chosen as a model analyte was examined, yielding a sensitivity of 350 and 80 microA M(-1) cm(-2), respectively, for polypyrrole-alginate and alginate biosensors.

Alginates↗
PubMedDate not supplied

Antigen-antibody binding kinetics for biosensors: the fractal dimension and the binding rate coefficient.

The diffusion-limited binding kinetics of antigen (or antibody or substrate) in solution to antibody (or antigen or enzyme) immobilized on a biosensor surface is analyzed within a fractal framework. The change in the fractal dimension, Df, is in the same direction as that in the forward binding rate coefficient, k1. An increase or decrease in the fractal dimension, Df leads to an increase or decrease in the forward binding rate coefficient, k1, respectively, irrespective of whether the antigen or the antibody is immobilized on the biosensor surface. For example, an increase in the concentration of IgG (MRC OX-19) (antigen) in solution from 1 to 10 micrograms/mL bound to polyclonal sheep anti-mouse IgG (antibody) immobilized on immunomagnetic beads leads to decreases in Df from 1.93 to 0.517 and in k1 from 2.72 to 0.064, respectively. The different examples analyzed and presented together indicate one means by which the forward binding rate coefficient, k1, may be controlled, that is, by changing the fractal dimension or the disorder on the surface. The versatility of the analysis is indicated by applying it to different examples for both types of systems, wherein either the antigen or antibody is immobilized on the surface. The analysis should assist in improving the stability, sensitivity, and response time of biosensors.

Antigen-Antibody Reactions↗
PubMedDate not supplied

Single- and dual-fractal analysis of hybridization binding kinetics: biosensor applications.

The diffusion-limited hybridization kinetics of analyte in solution to a receptor immobilized on a biosensor or immunosensor surface is analyzed within a fractal framework. The data may be analyzed by a single- or a dual-fractal analysis. This was indicated by the regression analysis provided by Sigmaplot. It is of interest to note that the binding rate coefficient and the fractal dimension both exhibit changes in the same direction for both the single-fractal and the dual-fractal analysis examples presented. For example, for a single-fractal analysis and for the hybridization of 10 nM 16CFl (oligonucleotide) to 16B immobilized via sulfosuccinimidyl-6-(biotinamido)hexanoate and streptavidin using chemical and thermal regeneration (Abel, A. P.; Weller, M. G.; Duveneck, G. L.; Ehrat, M. Widmer, H. M. Anal. Chem. 1996, 68, 2905-2912), an increase in the fractal dimension, Df from 1.211 (chemical regeneration) to 1.394 (thermal regeneration), leads to an increase in the binding rate coefficient, k, from 86.53 (chemical regeneration) to 100.0 (thermal regeneration). An increase in the degree of heterogeneity on the biosensor surface leads to an increase in the binding rate coefficient. When a dual-fractal analysis was utilized, an increase in the fractal dimension value from Df1 to Df2 leads to an increase in the binding rate coefficient value from k1 to k2. The fractional order of dependence of the binding rate coefficient, k1, on (a) the analyte (rRNA) concentration in solution and (b) on the fractal dimension, Df1, for the hybridization kinetics to detect Listeria species (Fliss, R.; St-Laurent, M.; Emond, E.; Simard, R. E.; Lemieux, R.; Ettriki, A.; Pandian, S. Appl. Microbiol. Biotechnol. 1995, 43, 717-724.) further reinforces the fractal nature of the system. The binding rate coefficient(s) expressions developed as a function of the analyte concentration in solution and the fractal dimension are of particular value since they provide a means to better control of biosensor or immunosensor performance.

Biosensing Techniques↗
PubMed2004

Coupling a natural receptor protein with an artificial receptor to afford a semisynthetic fluorescent biosensor.

An artificial receptor and a signal transducer have been engineered on a lectin (saccharide-binding protein) surface by a post-photoaffinity labeling modification method. Saccharide binding can be directly and selectively read out by the fluorescence changes of the fluorophore via photoinduced electron transfer (PET) mode. Fluorescence titration with various saccharides reveals that molecular recognition by the artificial receptor is successfully coupled to the native binding site of the lectin, producing a novel fluorescent saccharide biosensor showing modulated specificity and enhanced affinity. Designed cooperativity between artificial and native molecular recognition modules was quantitatively demonstrated by the comparison of the binding affinities, and it represents a new strategy in molecular recognition. By using appropriate artificial receptors and various native lectins, this approach may provide many new semisynthetic biosensors for saccharide derivatives such as glycolipids and glycopeptides/proteins. An extended library of lectin-based biosensors is envisioned to be useful for glycome research, a newly emerging field of the post-genomic era.

Binding Sites↗
PubMed2001

Direct biosensor immunoassays for the detection of nonmilk proteins in milk powder.

The low prices of some nonmilk proteins make them attractive as potential adulterants in dairy products. An optical biosensor (BIACORE 3000) was used to develop a direct and combined biosensor immunoassay (BIA) for the simultaneous detection of soy, pea, and soluble wheat proteins in milk powders. Affinity-purified polyclonal antibodies raised against the three protein sources were immobilized in different flow channels (Fcs) on the biosensor chip (CM5). Dissolved milk powders were injected (20 microL injections at 20 microL min(-1)) through the serially connected Fcs, and the antibody-bound plant proteins were detected directly. The total run time between samples, including a regeneration step with 5 microL of 10 mM HCl, was 5 min. The limits of detection in milk powder were below 0.1% of plant protein in the total milk protein content. The antibodies also recognized some proteins from other plant sources, which made this BIA even more suitable as a broad screening assay for nonmilk proteins.

Animals↗
PubMed2005

Disposable biosensor test for organophosphate and carbamate insecticides in milk.

A highly sensitive and rapid biosensor test based on disposable screen-printed thick-film electrodes was developed, which is suitable for monitoring organophosphate and carbamate residues in foods of animal origin with increased fat contents such as milk. The wild-type enzyme was combined with three engineered variants of Nippostrongylus brasiliensis acetylcholinesterase (NbAChE), to obtain enhanced sensitivity. The sample pretreatment could be reduced to a minimum. There was no extraction or fat removal necessary. With the biosensor test paraoxon concentrations down to 1 microg/L could be detected in milk. The detection limit for carbaryl was 20 microg/L. Recovery rates for paraoxon and carbaryl in milk samples lay between 89 and 107%. Ten milk samples from local markets were tested both with the biosensor test and with standard chromatographic multiresidue methods. Two milk samples caused AChE inhibition rates of >50%. Accordingly, 4 microg/L tebufenpyrad, 4 microg/L tetraconazole, and 2 microg/L bifenthrin were detected in one of these milk samples. The other milk sample contained 2 microg/L tebufenpyrad.

Acetylcholinesterase↗
PubMed2006

Sensitivity and specificity improvement of an ion sensitive field effect transistors-based biosensor for potato glycoalkaloids detection.

Butyryl cholinesterase of different origin along with variations of the time of enzyme immobilization on the potentiometric transducer surface is offered to control the ion sensitive field effect transistor (ISFET)-based biosensor sensitivity. Because butyryl cholinesterase has been already used to develop the sensors for heavy metals, organophosphorus/carbamate pesticides, and steroidal glycoalkaloids analysis, the present study has been focused on the investigation and adjustment of the ISFET-based biosensor specificity exclusively to the glycoalkaloids. Utilization of ethylendiaminetetracetate (a complexon of heavy metal ions) and phosphotriesterase (a highly efficient catalyst for the hydrolysis of organophosphorus compounds) enabled the highly specific determination of glycoalkaloids at the background of lead and mercury (up to 500 microM of ions concentration) and paraoxon (up to 100 microM of pesticide concentration). The developed biosensor has been validated for glycoalkaloids detection in potato varieties cultivated in Ukraine, and the results obtained are compared to those measured by the methods of HPLC and TLC.

Alkaloids↗