Magnetic immunosensors

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]. 

G.H. Kim, A.G. Rand, and S.V. Letcher, Impedance characterization of a piezoelectric immunosensor. Part II Salmonella typhimurium detection using magnetic enhancement. Biosens. Bioelectron. 18, 91-99 (2003). 

G. Liu and Y. Lin, Electrochemical magnetic immunosensor based on gold nanoparticle labels. J. Nanosci. Nanotech. 5, 1060-1065 (2005). 

This configuration based on the use of two surfaces, magnetic beads for immunoassay and screen-printed electrodes for electrochemical detection, allows to obtain a faster and a more sensitive detection of the immunoreaction than using a unique surface (screen-printed electrode) in this case it is possible to perform the electrochemical measurement in faster times (less then 30 min) and improve the sensitivity (around two magnitude orders). For this reason, this approach is advised in the development of an electrochemical immunosensor specific to any analyte. 

Fig. 25.7. Calibration curve for PCB28 obtained using the electrochemical immunosensor based on magnetic beads and screen-printed electrodes. IgG anti-PCB28 lOOpg/mL PCB28-AP diluted 1 1000.

The detection limit (DL) of the electrochemical immunosensor based on magnetic beads has been estimated to be equal to 8 x 10-3 ng/mL. This depends on the affinity of antibodies for antigen and is defined as the lowest analyte concentration which can be distinguished and is calculated by evaluation of the mean of the blank solution (containing the tracer only) response minus two times the standard deviations [35]. 

An extraction procedure performed by sonication method for dried marine sediments and soil followed by the analysis of the extracts using an electrochemical immunosensor based on magnetic beads and carbon screen-printed electrodes is described in the protocol (see Procedure 25 in CD accompanying this book). 

In the traditional format, screen-printed electrodes are used as solid phase to carry out the immunoassay and as signal transducers. In recent years, different kinds of beads (glass, graphite particles or magnetic particles) have been used as solid phase to perform the immunoassay. For this reason, it is possible to use a new approach in the immunosensor construction coupling beads to screen-printed electrodes. 

PCB analysis using immunosensors based on magnetic beads and carbon screen-printed electrodes in marine sediment and soil samples... 

ELECTROCHEMICAL IMMUNOSENSOR USING MAGNETIC BEADS AS SOLID PHASE AND CARBON SCREEN-PRINTED ELECTRODES (SPCES) AS TRANSDUCERS... 

Centi, S., S. Laschi, and M. Mascini. 2007. Improvement of analytical performances of a disposable electrochemical immunosensor by using magnetic beads. Talanta 73 394—399. 

Horseradish peroxidase (HRP) is an important peroxidase that contains heme, which is the protein active site with the resting state of the heme iron, Fe(III), as prosthetic group. It can catalyze the dependent one-electron oxidation of a great variety of substrates, and has been commonly employed to construct biosensors (Hai-Li Zhang et al. 2008). Peroxidase is the most frequently used enzyme for the construction of immunosensors. Successful immobilization of horseradish peroxidase on modified magnetic particles and their employment in the amperometric biosensors are mentioned in (Hai-Li Zhang et al. 2008 Yu et al. 2006). 

Sheng-Fu Wang, Tan Yu-Mei (2007) A novel amperometric immunosensor based on Fe O magnetic nanoparticles/chitosan composite film for determination of ferritin. Anal Bioanal Chem 387 703-708... 

A model immunosensor based on a labeling method using gold nanoparticles (AuNPs) and electrochemical detection is developed. Microparamagnetic beads (MB) as primary antibody immobilization platforms and AuNPs modified with a secondary antibody as high sensible electrochemical labels have been used. The carbon electrode used as transducer incorporates a magnet that allows the collection/ immobilization on its surface of the immunological sandwich attached to the MB. 

Key words Gold nanoparticles, Protein analysis, Magnetic beads, Human IgG, Immunosensor,... 

The FABS, whose working principle was very similar to that of the AFM biosensor, was a cantilever-based immunosensor [7]. However, its configuration was much simpler than that of the AFM. Rather than using a piezoceramic translator to pull on intermolecular bonds, it used magnetic particles, which eliminated the need to manually position a tip and sample next to each other with picometer precision and stability. The cantilever-beam force transducer was the only element of the AFM retained by the FABS. 

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