Study On The Novel Immunosensor Based On Fe₃O₄ Magnetic Nano-particles

Fe₃O₄ magnetic nanoparticles were prepared using co-precipitation technology by the reaction between FeSO4 and FeCl3, and Fe₃O₄/Au magnetic nanoparticles were prepared on the basis of Fe₃O₄, then the surface of the magnetic nanoparticles were functionalized by the different means.The antibody were immobilized on the surface of the magnetic particles with absorption or covalent bond. The resulting magnetic bio-nanoparticles with antibody were attached onto the surface of solid paraffin carbon paste electrode (SPCE) with the help of a permanent magnet to construct new immunosensors. These immunosensors possess the advantages of high sensitivity, easy to use, easy regeneration etc.This paper has done some studies according to the focus problems of electrochemical bio-sensors at present, namely, how to develop simple, reliable methods to immobilize biomaterials on the surface of substrate electrode, and keep high stability and activity of enzyme, antigen, and antibody.1. Cysteine (Cys) molecules were irreversible adsorbed on the nano- Fe₃O₄ surface. Then, the modification of solid paraffin carbon paste electrode with nano-Fe₃O₄ by chemical adsorption of glutaraldehyde (GA) was achieved. Finally, goat anti human immunogloblin G (anti-IgG) were covalently immobilized on the electrode by glutaraldehyde (GA) to make a renewable potentiometric immunosensor. The immunosensor showed a specific response to human immunogloblin G (IgG) in the range of 0.1-1.2 ng/mL with a detection limit of 0.023 ng/mL. The immunosensor was made with facility, low-cost and used expediently. The immunosensor based on magnetic powder was renewable conveniently. The immunosensor with better stability and higher sensitivity can be used extensively in biomedical and clinical detection.2. The surface of the magnetic Fe₃O₄ nanoparticles was functionalized with 3- aminopropyltri ethoxysilane (APS) to form amino-modified Fe₃O₄. The anti-IgG was covalented to amino modified particles by using glutaraldehyde to form magnetic bio-nanoparticles. The resulting magnetic bio-nanoparticles were attached onto the surface of solid paraffin carbon paste electrode (SPCE) with the help of a permanent magnet to construct a new amperometic immunosensor. This immunosensor was used to analyze human immunoglobulin G by double antibody sandwich method. The linear range was from 2.5 to 400 ng/mL. The detection limit was 0.75 ng/mL. The magnetic nanoparticles offered a good microenvironment for retaining the bioactivity of antibody and increase the amount of loaded. The immunosensor can regenerate the surface with convenience and rapid methods.3. Fe₃O₄/Au magnetic nanoparticles were prepared firstly, and then the surfaces of the magnetic nanoparticles were amino functionalized with thiourea. The carcinoembryonic antigen antibody (anti-CEA) was covalented to amino-modified particles by using glutaraldehyde. The resulting magnetic bio-nanoparticles were attached onto the surface of solid paraffin carbon paste electrode with the help of a permanent magnet to construct a new amperometic immunosensor. This immunosensor was used to determinate carcinoembryonic antigen (CEA) with competitive immunoassay. The sensitivity was improved greatly by the horseradish peroxide enzyme catalytic and hydrogen peroxide reaction. The linear range was from 2 to 160 ng/mL. The detection limit was 0.57 ng/mL. The simple manipulations of construction, low cost, high sensitivity, fast response, sharp specificity and easy regeneration of the sensing platform were main advantages of the immunosensor.4. Fe₃O₄/Au magnetic nanoparticles were attached on the surface of solid paraffin carbon paste electrode with the help of a permanent magnet. Nano-Au were assembly onto the magnetic nano-particles using thiourea. The anti-CEA were adsorptive immobilized on the nano-Au to make a amperometic immunosensor. The resulting immunosensor offers a high sensitivity for the detection of CEA and has good correlation for detection of CEA in the range of 0.2 to 500 ng/mL with a detection limit of 0.07 ng/mL estimated at a signal-to-noise ratio of 3. Gold nanoparticles bilayer can increase the amount of the antibody loaded and keep the high activity of the anti-CEA. It can regenerate conveniently by take off the magnete. The immunosensor have high sensitivity and wide linear range. The practical effect of the immunosensor is good.