Fabrication Of Disposable Amperometric Immunosensors Using Functionalized Nanomaterials For Signal Amplification

The amperometric immunosensors based on functionalized nanomaterials, which combine the highly specific electrochemical immunosensing techniques with the various properties of nanomaterials to carry numerous tags for signal amplification, have been considered to be a promising analytical method due to the advantages of ultrahigh sensitivity and low detection limit. Nowadays, they have been extensively applicated in clinical diagnostics, pharmaceutical analyses, extended to quality control of environment and food field. This thesis focuses on the development of disposable amperometric immunosensors based on screen printed electrodes, and the construction of signal amplification platform on the basis of functionalized nanoprobes.1. Disposable electrochemical immunosensor by using carbon sphere/gold nanoparticles composite as label for signal amplificationThis work designed a simple, sensitive, and low-cost immunosensor for the detection of protein marker by using carbon sphere/gold nanoparticles (CNSs/AuNPs) composite as an electrochemical label. The nanoscale carbon spheres, prepared with a hydrothermal method by using glucose as raw material, were used to load AuNPs for labeling antibody by electrostatic interaction, which provided a feasible pathway for electron transfer due to the remarkable conductivity. The disposable immunosensor was constructed by coating a polyethylene glycol (PEG) film on a screen-printed carbon-working electrode and then immobilizing capture antibody on the film. With a sandwich-type immunoassay format, the analyte and then CNSs/AuNPs-labeled antibody were successively bound to the immunosensor. The bound AuNPs were finally electro-oxidized in0.1M HC1to produce AuCl-4for differential pulse voltammetric (DPV) detection. The high-loading capability of AuNPs on CNS for the sandwich-type immunorecognition led to obvious signal amplification. By using human immunoglobulin G (HIgG) as model target, the DPV signal of AuNPs after electro-oxidized at optimal potential of+1.40V for40s showed a wide linear dependence on the logarithm of target concentration ranging from10pg mL-1to10ng mL-1. The detection limit was around9pg mL-1. The immunosensor showed excellent analytical performance with cost effectivity, good fabrication reproducibility, and acceptable precision and accuracy, providing significant potential application in clinical analysis.2. Pt nanodendrites functionalized graphene nanosheet:Preparation, electrocatalysis, and application in immunosensing as electrochemical tagPlatinum nanodendrites (PtNDs) functionalized graphene nanosheet (GS) was used as an electrochemical label to design a highly sensitive disposable immunosensor. The immunosensor was constructed by coating a polyethylene glycol (PEG) film on a screen-printed carbon-working electrode and then immobilizing capture antibody on the film. The PtNDs/GS, prepared by in-situ deposition of Pt nanoparticles, was labeled to antibody as a detection probe for immunoreaction. With a sandwich-type immunoassay format, the analyte and then PtNDs/GS-labeled antibody were successively captured to the immunocomplex and showed strong electrocatalytic activity toward oxygen reduction. The use of GS carrier offered a high amount of PtNDs on each immunoconjugate and provided a feasible pathway for electron transfer, hence amplified the detectable signal from the electro-reaction of dissolved oxygen. Under optimal conditions, a low limit of detection down to pg/mL was achieved for human IgG. Using dissolved oxygen as signal reporter, the detection process avoided deoxygenation. The immunosensor showed excellent analytical performance with cost effectivity, good fabrication reproducibility, acceptable stability, precision and accuracy, indicating potential applications in clinical diagnostics.