Tianhua Li

Fe3O4/Au magnetic nanoparticle amplification strategies for ultrasensitive electrochemical immunoassay of alfa-fetoprotein

Background The purpose of this study was to devise a novel electrochemical immunosensor for ultrasensitive detection of alfa-fetoprotein based on Fe3O4/Au nanoparticles as a carrier using a multienzyme amplification strategy. Methods and results Greatly enhanced sensitivity was achieved using bioconjugates containing horseradish peroxidase (HRP) and a secondary antibody (Ab2) linked to Fe3O4/Au nanoparticles (Fe3O4/Au-HRP-Ab2) at a high HRP/Ab2 ratio. After a sandwich immunoreaction, the Fe3O4/Au-HRP-Ab2 captured on the electrode surface produced an amplified electrocatalytic response by reduction of enzymatically oxidized hydroquinone in the presence of hydrogen peroxide. The high content of HRP in the Fe3O4/Au-HRP-Ab2 could greatly amplify the electrochemical signal. Under optimal conditions, the reduction current increased with increasing alfa-fetoprotein concentration in the sample, and exhibited a dynamic range of 0.005–10 ng/mL with a detection limit of 3 pg/mL. Conclusion The amplified immunoassay developed in this work shows good precision, acceptable stability, and reproducibility, and can be used for detection of alfa-fetoprotein in real samples, so provides a potential alternative tool for detection of protein in the laboratory. Furthermore, this immunosensor could be regenerated by simply using an external magnetic field.

A Three-Dimensional, Magnetic and Electroactive Nanoprobe for Amperometric Determination of Tumor Biomarkers

A novel electrochemical immunosensor for tumor biomarker detection based on three-dimensional, magnetic and electroactive nanoprobes was developed in this study. To fabricate the nanoprobes, negatively charged Fe3O4 nanoparticles (Fe3O4 NPs) and gold nanoparticles (Au NPs) were first loaded on the surface of multiple wall carbon nanotubes (MCNTs) which were functioned with redox-active hemin and cationic polyelectrolyte poly(dimethyldiallylammonium chloride) (PDDA). Using alpha fetoprotein (AFP) as a model analyte, AFP antibody (anti-AFP) was absorbed on the surface of Au NPs, bovine serum albumin (BSA) was then used to block sites against non-specific binding, and finally formed anti-AFP/Au NPs/Fe3O4/hemin/MCNTs named anti-AFP nanoprobes. When the target antigen AFP was present, it interacted with anti-AFP and formed an antigen-antibody complex on the nanoprobe interface. This resulted in a decreased electrochemical signal of hemin for quantitative determination of AFP when immobilized onto the screen-printed working electrode (SPCE). The results showed that the nanoprobe-based electrochemical immunosensor was sensitive to AFP detection at a concentration of 0.1 to 200 ng·mL−1 with a detection limit of 0.04 ng·mL−1, it also demonstrated good selectivity against other interferential substances. The electroactive nanoprobes can be massively prepared, easily immobilized on the SPCE for target detection and rapidly renewed with a magnet. The proposed immunosensor is fast, simple, sensitive, stable, magnet-controlled, nontoxic, label-free and reproducible.

One novel composite nano-particles membrane modified amperometric immunosensor for Escherichia coli in polluted waters

A novel amperometric immunoassay for identification of Escherichia coli (E.coli) in a matrix containing zirconium dioxide nanoparticles (ZrO<inf>2</inf>) was described. Firstly, the antibody of E.coli (anti E.coli) was immobilized on a glassy carbon electrode (GCE) modified with carbon nanotubes (CNTs) using ZrO<inf>2</inf> nanoparticles, colloidal gold (Au) and poly-Lysine (pLL) composite membrane (ZrO<inf>2</inf>-Au-pLL-anti-E.coli) aiming to maintain the antibodys bioactivity. Then one novel sebacato-bridged Co(□) complex Co(suc)(bpy)(H<inf>2</inf>O)<inf>2</inf> (referred to as CoL, suc=succinic acid; bpy=2,2′-bipyridine) was adsorbed onto the surface of ZrO<inf>2</inf>-Au-pLL-anti-E.coli composite membrane, thus the immunosensor (GCE|CNTs|ZrO<inf>2</inf>-Au-pLL-anti-E.coli|CoL) for determination of E.coli was constructed based on one step immunoreaction using cyclic voltammetry (CV) method. CoL can be employed as an electron transfer mediator for catalytic activity detection of H<inf>2</inf>O<inf>2</inf>. After the immunosensor was incubated with E.coli solution at room temperature for 20 min, the electron transfer access of CoL to H<inf>2</inf>O<inf>2</inf> was partly inhibited, which leads to a linear decrease of the catalytic efficiency to H<inf>2</inf>O<inf>2</inf>. The immunosensor was employed to determine E.coli in samples and the results were consistent to the tradition enzyme-linked immunosorbent assays (ELISA) method. The proposed ampero metric immunosensor was sensitive, quick and disposable, which was suitable for determination of E.coli in polluted waters for public health and environmental protection.

Immunoassay by hydride generation-atomic fluorescence spectrometer using arsenic absorbed Fe 3 O 4 @Au nanoparticles as label

A novel immunoassay method based on hydride generation-atomic fluoresce spectrometer (HG-AFS) with arsenic (As) absorbed Fe3O4@Au (Fe3O4@Au-As) nanoparticles as tags to the antibody for the rapid and early diagnosis of α-fetoprotein (AFP) in primary carcinoma of the liver is proposed. The new approach combined the use of Fe3O4@Au-As nanoparticles labeled antibody, and HG-AFS detection for sandwich-type immunoassay. Firstly, Fe3O4@Au-As nanoparticles were prepared. Then Fe3O4@Au-As composite is used to immoblize HRP-labeled anti-AFP as secondary antibody (bionanospheres). The bionanospheres were characterized by transmission electron microscopy (TEM), and ultraviolet visible spectroscopy (UV-Vis). Sandwich-type protocol was successfully introduced to develop a new high-efficiency HG-AFS immunoassay. An important advantage of HG-AFS is high sensitivity to the detection of As. And in the immune-complex the concentration of As is high and has a linear relationship with AFP antigen, which could enlarge the signals. The antigen concentration, thus, was determined by measuring the arsenic in the immune complex with HG-AFS, which is quite promising for the detection of low concentration AFP at early stage of primary carcinoma of the liver.