Applications Of Nanomaterials In Electrochemical And Fluorescent Immunoassays

Because of their unique optical, electrical and catalytic properties, nanomaterials have shown attractive prospects in electrical and computer engineering, energy storage and conversion, as well as analytical chemistry for life science. Immunoassays based on the specific reactions between antibody and antigen and electrochemical, optical sensing technologies have been widely studied because of their inherent advantages such as excellent selectivity, low cost, convenient operation and easy to miniaturization. Immunoassays have provided a promising platform for the detection of biomarkers, cells, DNA, and so on. Exploring ways to simplify immunoassay process and to improve analytical sensitivity has gained an increasing interest. In this work, by combining technologies of materials science, chemistry and biology, we focus on the applications of advanced nanomaterials in electrochemical and fluorescent immunoassays. The main contents are as follows:1. Electrochemical Immunoassay for the Prostate Specific Antigen Using Ceria Mesoporous NanospheresA sensitive electrochemical immunoassay for the prostate specific antigen (PSA) was developed. An immunoelectrode was fabricated by coating a glassy carbon electrode with multiwalled carbon nanotubes, poly(dimethyldiallylammonium chloride), CeO2 and PSA antibody (in this order) using the layer-by-layer method. The immunosensor is then placed in a sample solution containing PSA and o-phenylenediamine (OPD). It is found that the CeO2 nanoparticles facilitate the electrochemical oxidation of OPD, and this produces a signal for electrochemical detection of PSA that depends on the concentration of PSA. There is a linear relationship between the decrease in current and the concentration of PSA in the 0.01 to 1000 pg·mL-1 concentration range, and the detection limit is 4 fg·mL-1. The assay was successfully applied to the detection of PSA in serum samples. This new differential pulse voltammetric immunoassay is sensitive and acceptably precise, and the fabrication of the electrode is well reproducible.2. Fluorescent Immunosensor Based on CuS Nanoparticles for Sensitive Detection of Cancer BiomarkerA novel fluorescent immunosensor was developed for highly sensitive detection of human prostate cancer biomarker prostate specific antigen (PSA) using CuS nanoparticles (CuS NPs) as labels. In the presence of CuS NPs, nonfluorescent substrate o-phenylenediamine (OPD) could be oxidized into the stable fluorescent product 2,3-diamiophenazine (OPDox) at physiological pH. Throughout the reaction, no other oxidizing agents (e.g. hydrogen peroxide) were needed. The fluorescent emission maximum of OPDox was at 558 nm. The relatively mild oxidation conditions made the immunoassay more robust, reliable and facile. The proposed immunoassay exhibited high sensitivity and specificity for the detection of PSA. The linear relationship between fluorescent signals and the concentration of PSA was obtained in the range of 0.5 pg·mL-1-50 ng-mL"1, with the detection limit of 0.1 pg·mL-1 (S/N=3). This fluorescent immunoassay can be used as a promising platform for the detection of a variety of other biomarkers.