Analytical Application Of Biosensing Technology Based On Nano Materials In The Food Safty

Nano-materials, the grain size of which are less than100nm, areformed by nano-particles. Due to their small size, they have some unique characters inoptics, electricity, magnetism, chemistry and catalytic performance. With the help ofnano-materials in the field of biosensing technology, the performance of biosensorscould be greatly improved accordingly. In recent years, the chemical contamination offood raw materials, the use of illegal additives in animal husbandry, and geneticengineering technology make the food no longer safe, which raise the foodbornediseases caused by food contamination. Thus, food safety issues have attracted a lot ofconcerns around the world. This dissertation focuses on developing a series ofbiosensing techniques based nano-particles such as gold nano-particles(GNP),quantum dots(QD), to detect several small molecular toxins in food safety issuesincluding ochratoxin A(OTA), clenbuterol(CL). The detailed methods are as follows:(1) A sensitive electrochemical immunosensor based on Polythionine/gold fixinghapten was developed for the determination of ochratoxin A (OTA), a common toxiccontaminant in various kinds of agricultural products. Firstly, polythionine film layerwas built on the the surface of glass carbon electrode (GCE) as a positive substrate toassemble gold nanoparticles layer, which could enhance the surface loading ofochratoxin A-ovalbumin (OTA-OVA) conjugates and improve the sensitivity inelectrochemical readouts. After competition of the limited anti-OTA mousemonoclonal antibody between immobilized hapten and OTA analyte in sample solution,alkaline phosphatase (ALP)-labeled horse anti-mouse immunoglobulin G(IgG)antibody was selectively bound onto the surface of the electrode, affording an indicatorfor OTA concentration in the sample. Electrochemical response arising from theoxidation of enzymatic product of1-naphthyl phosphate was observed to be inverselyproportional to the logarithm of OTA concentration with a detection limit as low as2.5ng/mL. Furthermore, a negligible matrix effect and good recoveries were obtained inthe determination of corn samples, evidencing the feasibility of the proposed methodfor accurate determination of OTA in corn samples.(2) A convenient, specific, and highly sensitive electrochemical immunosensorbased on signal amplification by gold nanoparticle was developed for the detection ofclenbuterol(CL).1,6-hexanedithiol monolayer was firstly self-assembled on the surface of a gold electrode, which could mediated the assembly of ananoparticles(GNP) layer through Au-S effect, to enhance the surface loading ofClenbuterol-Bovine Serum Albumin (CL-BSA) conjugates and improve theelectrochemical sensitivity significantly. After that, the sample solution was cultivatedwith given concentration of anti-CL mouse monoclonal antibody, which then reactedwith the CL-BSA conjugates on the surface of the electrode. So the antibody bindingto the electrode surface had a mathematical relationship with the amount of CL in thesample. Alkaline phosphatase (ALP)-labeled horse anti-mouse immunoglobulin G (IgG)antibody was bound onto the surface of the electrode with the mouse antibody, so as toarise a electrochemical signal from the oxidation of enzymatic product of1-naphthylphosphate. The electrochemical immunosensor is convenient, specific, and highlysensitive, with detection limit as low as20pg/mL.(3) A convenient, specific, and sensitive sensing technology was developed todeterminate melamine based on fluorescence quenching resulted from QuantumDot(QD) aggreagtion, with the fact that only thymine of all the four DNA bases couldhighly recognize melamine in aqueous medium by the form of triple H-bonds with it.Amino marked thymine was conjugated with mercaptoacetic acid modified CdSe/ZnSQD, which could aggregate the QD by form the special triple H-bonds as long as thesample contained melamine, resulting in fluorescence quenching. The experimentalresults showed that the dynamic linear range for melamine detection was from5μmol/L to2mmol/L, with a detection limit of3.9μmol/L.