Improvement of enzymatic activity and lifetime of Langmuir-Blodgett films by using submicron SiO2 particles

Flow-injection electrochemical immunosensor for the detection of human IgG based on glucose oxidase-derivated biomimetic interface

A newly flow-through electrochemical immunosensor for monitoring IgG in human serum has been developed by using core-shell SiO(2)/Au nanocomposites and poly(amidoamine) G4 dendrimer as matrices. The ferrocenecarboaldehyde-labeled anti-IgG biomolecules were initially chemisorbed onto the nanoparticle surface, and then glucose oxidase (GOx), as a blocking reagent instead of bovine serum albumin (BSA), was backfilled onto the modified surface. The formation of the antibody-antigen complex by a simple one-step immunoreaction between the immobilized anti-IgG and IgG in sample solution introduced a barrier of direct electrical communication between the immobilized GOx and the base surface, and decreased the immobilized GOx toward the catalytic oxidation of glucose. The performance and factors influencing the performance of the immunosensor were evaluated. Under optimal conditions, the linear range of the developed immunosensor by using GOx as enhancer was from 5.0 x 10(-6) to 9.6 x 10(-4)mol/L with a detection limit of 8.0 x 10(-7)mol/L IgG (at 3delta), while the detection limit by using BSA was 1.5 x 10(-5)mol/L IgG (at 3delta) with the linear range from 3.5 x 10(-5) to 1.2 x 10(-3)mol/L. The selectivity, reproducibility and stability of the proposed immunosensor were acceptable. The IgG contents in 37 human serum samples obtained by the proposed method are identical with the data of clinical laboratory.

Amplification of the antigen–antibody interaction from quartz crystal microbalance immunosensors via back-filling immobilization of nanogold on biorecognition surface

A new quartz crystal microbalance immunoassay method based on a novel transparent immunoaffinity reactor was developed for clinical immunoassay. To construct such an affinity reactor, resonators with a frequency of 10 MHz were fabricated by affinity binding of functionalized gold nanoparticles (nanogold) to quartz crystal with immobilized specific ligand for the label-free analysis of the affinity reaction between a ligand and its receptor. [Recombinant human tumor markers, carcinoembryonic antigen (CEA) was chosen as a model ligand.] The binding of target molecules onto the immobilized antibodies decreased the sensor's resonant frequency, and the frequency shift was proportional to the CEA concentration in the range of 3.0-50 ng/ml with a detection limit of 1.5 ng/ml at a signal/noise ration of 3. A glycine-HCl solution (pH 2.3) was used to release antigen-antibody complexes from the biorecognition surface. Good reusability was exhibited. Moreover, spiking various levels of CEA into normal human sera was diagnosed using the proposed immunoassay. Analytical results show the precision of the developed immunoassay is acceptable, implying a promising alternative approach for detecting CEA in clinical immunoassay. Compared with the conventional enzyme-linked immunosorbent assay, the proposed immunoassay system was simple and rapid without multiple labeling and separation steps. Importantly, the proposed immunoassay system could be further developed for the immobilization of other antigens or biocompounds.

Direct electrochemical immunoassay based on a silica nanoparticles/sol–gel composite architecture for encapsulation of immunoconjugate

A highly hydrophobic and non-toxic colloidal silica nanoparticle/polyvinyl butyral sol-gel composite membrane was prepared on a platinum wire electrode. With diphtheria-toxoid (D-Ag) as a model antigen and encapsulation of diphtheria antibody (D-Ab) in the composite architecture, this membrane could be used for reagentless electrochemical immunoassay. It displayed a porous and homogeneous composite architecture without the aggregation of the immobilized protein molecules. The formation of immunoconjugate by a simple one-step immunoreaction between D-Ag in sample solution and the immobilized D-Ab introduced the change in the potential. Under optimal conditions, the D-Ag analyte could be determined in the linear ranges from 10 to 800 ng ml(-1) with a relatively low detection limit of 2.3 ng ml(-1) at 3delta. The D-Ag immunosensor exhibited good precision, high sensitivity, acceptable stability, accuracy, and reproducibility. This composite membrane could be used efficiently for the entrapment of different biomarkers and clinical applications.

Development of quartz-crystal-microbalance-based immunosensor array for clinical immunophenotyping of acute leukemias

An integrated piezoelectric immunosensor array has been developed to immunophenotype acute leukemias in clinic. Each quartz crystal microbalance (QCM) was fabricated with plasma-polymerized film of n-butylamine, nanogold particles, and protein A (PA) to be used to immobilize antibodies in orientation. Leukemic lineage-associated monoclonal antibodies were separately immobilized onto the nanogold-PA-modified surface of the crystals, which were constructed by a 2 x 2 type of probes forming a QCM-based immunosensor array. The main detection conditions were investigated, including the immobilization amount of antibodies, pH, immunoreaction time, sample dilution ratio, etc. The immunophenotyping feasibility of the new technique was investigated through simultaneously analyzing Jurkat cells by the immunosensor array method, immunohistochemistry, and flow cytometry. It was found that the developed technique could readily identify leukemia samples in 5 min and might monitor dynamically the immunoreaction processes. Moreover, comparison studies were carried out for CD antigens expressed on the nucleated cells isolated from 96 acute leukemic patients and 24 normal subjects using the QCM-based immunosensor method and the fluoroimmunoassay. Results obtained by immunophenotyping patients' samples with the immunosensor-based method achieved the rate of 88.93% in 768 groups of numerical data, where no significant statistical difference was observed between the two methods when checked by chi2 analysis (chi2 = 3.4, p > 0.05). This new immunosensor array showed the merits of high sensitivity, high specificity, good reproducibility, easy operation, and low cost. The results of specimen evaluation indicated that it might be clinically suitable for quantifying human differentiated leukocytes and immunophenotyping of acute leukemias.

Electrochemical detection of hepatitis B surface antigen using colloidal gold nanoparticles modified by a sol–gel network interface

BACKGROUND

A novel potentiometric immunosensor for the detection of hepatitis B surface antigen has been developed by self-assembling gold nanoparticles to a thiol-containing sol-gel network.

METHODS

A cleaned gold electrode was first immersed in a hydrolyzed (3-mercaptopropyl) trimethoxysilane sol-gel solution to assemble a three-dimensional silica gel, and then gold nanoparticles were absorbed onto the thiol groups of the sol-gel network. Finally, hepatitis B surface antibody was assembled onto the surface of the gold nanoparticles. The self-assembling procedure was characterized by cyclic voltammetry and electrochemical impedance spectroscopy. Detection is based on the change in potentiometric response before and after the antigen-antibody reaction.

RESULTS

Tests relating to the detection of hepatitis B surface antigen demonstrate that the potentiometric immunosensor exhibited a rapid potentiometric response (<4 min), with high sensitivity, good reproducibility, and long-term stability. The linear range was from 4 to 960 ng.mL(-1) with a detection limit of 1.9 ng.mL(-1) (S/N = 3) and the lifetime was 1 month.

CONCLUSION

Analytical results of several specimens using the developed technique showed satisfactory agreement with those from an ELISA method. This method shows promise for detecting HBsAg in clinical specimens.

Enzyme association with lipidic Langmuir-Blodgett films: interests and applications in nanobioscience

This review presents the recent advances in the achievement of organized proteo-lipidic nanostructures based on Langmuir-Blodgett technology and their potential applications in the nanobioscience area. By using the self-assembled properties of amphiphilic biomolecules at the air-water interface, the Langmuir-Blodgett (LB) technique offers the possibility to prepare ultrathin layers suitable for biomolecule immobilization at the molecular level. This review will provide a general overview of the enzyme association with preformed Langmuir-Blodgett films in connection with their potential applications in biosensing device developments, and then introduce the design of a new functionalised biomimetic nanostructure with oriented recognition site. The potential applications of such an organized proteo-lipidic nanostructure for biocatalysis investigations of an immobilised enzyme in a biomimetic situation and for the development of bioelectronic devices are finally discussed.

Structured thin films as functional components within biosensors

This review provides an introduction to the field of thin films formed by Langmuir-Blodgett or self-assembly techniques and discusses applications in the field of biosensors. The review commences with an overview of thin films and methods of construction. Methods covered will include Langmuir-Blodgett film formation, formation of self-assembled monolayers such as gold-thiol monolayers and the formation of multilayers by the self-assembly of polyelectrolytes. The structure and forces governing the formation of the materials will also be discussed. The next section focussed on methods for interrogating these films to determine their selectivity and activity. Interrogation methods to be covered will include electrochemical measurements, optical measurements, quartz crystal microbalance, surface plasmon resonance and other techniques. The final section is dedicated to the functionality of these films, incorporation of biomolecules within these films and their effect on film structure. Species for incorporation will include antibodies, enzymes, proteins and DNA. Discussions on the location, availability, activity and stability of the included species are included. The review finishes with a short consideration of future research possibilities and applications of these films.

Novel potentiometry immunoassay with amplified sensitivity for diphtheria antigen based on Nafion, colloidal Ag and polyvinyl butyral as matrixes

A novel potentiometry immunoassay with amplified sensitivity has been developed for the detection of diphtheria antigen (Diph) via immobilizing diphtheria antibody (anti-Diph) on a platinum electrode based on Nafion, colloidal Ag (Ag), and polyvinyl butyral (PVB) as matrixes in this study. The modified procedure was further characterized by electrochemical impedance spectroscopy (EIS) and cyclic voltammetry (CV). The influence and factors influencing the performance of resulting immunosensor were studied in detail. The resulting immunosensor exhibited sigmoid curve with log Diph concentrations, high sensitivity (51.4 mV/decade), wide linear range from 8 to 800 ng ml(-1) with a detection limit of 1.5 ng ml(-1), rapid potentiometric response (<3 min) and long-term stability (>6 months). Analytical results of clinical samples show that the developed immunoassay is comparable with the enzyme-linked immunosorbent assays (ELISAs) method, implying a promising alternative approach for detecting diphtheria antigen in the clinical diagnosis.