Sensor immunosensor

Fiber Optic Affinity Sensors, Immunosensors and Gene Sensors... 

Wherever an antibody assay is used now, there will be the prospect of producing an immunosensor for the same analyte. Therefore, the development of immunosensors is directed to obtain sensors with fast response, low detection limits, little preparation efforts, low price availability and high specificity. Thanks to the possibility of fabricating fast portable sensors, immunosensors now constitute a potential alternative to centralized and sophisticated bioanalytical systems. 

Alfonta, L., Bardea, A., Khersonsky, O., Katz, E., Willner, I. (2001). Chronopotentiometry and faradaic impedance spectroscopy as signal transduction methods for the biocatalytic precipitation of an insoluble product on electrode supports routes for enzyme sensors, immunosensors and DNA sensors. Biosens Bioelectron 16, 675-687. 

Oximetry Blood Gases Glucose Sensors Immunosensors... 

Inorganic ions, drugs, nucleic acids, proteins, and even cells are successful examples of imprinting. In this way, affinity sensors, receptor sensors, and catalytic sensors based on MIPs have been explored. For affinity sensors, immunosensor-like devices were prepared by a 2D MIP technique with molecular imprinting on chemisorbed alkanethiol SAMs then after necessary procedures, vitamins Ki, K2, E, cholesterol, and adamantine could be detected by the strong electrochemical signals yielded. The sensors for nucleic acids, cholesterol, and catechol derivatives can be fabricated first by their adsorption as a template on the ITO surface and then by the treatment of the electrode with adsorbed template using trimethyl chlorosilane from the gas phase. 

Enzyme Immunosensors. Enzyme immunosensors are enzyme immunoassays coupled with electrochemical sensors. These sensors (qv) require multiple steps for analyte determination, and either sandwich assays or competitive binding assays maybe used. Both of these assays use antibodies for the analyte of interest attached to a membrane on the surface of an electrochemical sensor. In the sandwich assay type, the membrane-bound antibody binds the sample antigen, which in turn binds another antibody that is enzyme-labeled. This immunosensor is then placed in a solution containing the substrate for the labeling enzyme and the rate of product formation is measured electrochemically. The rate of the reaction is proportional to the amount of bound enzyme and thus to the amount of the analyte antigen. The sandwich assay can be used only with antigens capable of binding two different antibodies simultaneously (53). 

The aim of our investigation was the development of the amperometric enzyme immunosensor for the determination of Klebsiella pneumoniae bacterial antigen (Ag), causes the different inflammatory diseases. The biosensing pail of the sensors consisted of the enzyme (cholinesterase) and antibodies (Ab) immobilized on the working surface of the screen-printed electrode. Bovine seiaim albumin was used as a matrix component. 

The working conditions of the immunosensor (enzyme and antigen concentrations, dilutions of the antibodies, pH of the buffer solution) were found. The cholinesterase immobilized demonstrated the maximum catalytic activity in phosphate buffer solution with pH 8.0. The analytical chai acteristics of the sensor - the interval of the working concentrations and detection limit - have been obtained. The proposed approach of immunoassay made possible to detect 5T0 mg/ml of the bacterial antigen. 

Particularly attractive for numerous bioanalytical applications are colloidal metal (e.g., gold) and semiconductor quantum dot nanoparticles. The conductivity and catalytic properties of such systems have been employed for developing electrochemical gas sensors, electrochemical sensors based on molecular- or polymer-functionalized nanoparticle sensing interfaces, and for the construction of different biosensors including enzyme-based electrodes, immunosensors, and DNA sensors. Advances in the application of molecular and biomolecular functionalized metal, semiconductor, and magnetic particles for electroanalytical and bio-electroanalytical applications have been reviewed by Katz et al. [142]. 

Electrogenerated chemiluminescence (ECL) has proved to be useful for analytical applications including organic analysis, ECL-based immunosensors, DNA probe assays, and enzymatic biosensors. In the last few years, the electrochemistry and ECL of compound semiconductor nanocrystallites have attracted much attention due to their potential applications in analytical chemistry (ECL sensors). 

Heideman R.G., H. Kooyman R. P., Greve J., Performance of a highly sensitive optical waveguide Mach-Zehnder interferometer immunosensor, Sensors and Actuators B 1993 10 209-217. 

A major disadvantage is that the direct sensor detection cannot distinguish between the sensor response to the specific analyte binding from the response to a possible nonspecific adsorption of other compounds. The nonspecific fouling from blood or blood serum seems to be one of the main barriers for practical application of immunosensors in medical diagnostics. 

Brynda E., Elomola J., Elouska M., Pfeifer P., Skvor J., Antibody networks for surface plasmon resonance immunosensors, Sensors Actuators B. 1999 54 132-136. 

Competitive immunoassays may also be used to determine small chemical substances [10, 11]. An electrochemical immunosensor based on a competitive immunoassay for the small molecule estradiol has recently been reported [11]. A schematic diagram of this immunoassay is depicted in Fig. 5.3. In this system, anti-mouse IgG was physisorbed onto the surface of an SPCE. This was used to bind monoclonal mouse anti-estradiol antibody. The antibody coated SPCE was then exposed to a standard solution of estradiol (E2), followed by a solution of AP-labeled estradiol (AP-E2). The E2 and AP-E2 competed for a limited number of antigen binding sites of the immobilized anti-estradiol antibody. Quantitative analysis was based on differential pulse voltammetry of 1-naphthol, which is produced from the enzymatic hydrolysis of the enzyme substrate 1-naphthyl phosphate by AP-E2. The analytical range of this sensor was between 25 and 500pg ml. 1 of E2. 

Y.-M. Zhou, Z.-Y. Wu, G.-L. Shen, and R.-Q. Yu, An amperometric immunosensor based on Nafion-modified electrode for the determination of Schistosoma japonicum antibody. Sensors and Actuators, B Chemical 89, 292-298 (2003). 

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