Abstract
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.
Highlights
In recent years, protein detection in biological samples has received considerable attention in disease diagnosis, food safety control, environmental monitoring and many other fields
The Fe3O4 NPs, Au NPs, multiple wall carbon nanotubes (MCNTs) and Au NPs/Fe3O4/hemin/MCNT nanocomposites were characterized by transmission electron microscopy (TEM)
After MCNTs were functioned with hemin and poly(dimethyldiallylammonium chloride) (PDDA), the negatively charged Fe3O4 NPs and Au NPs were assembled on the surface of MCNTs through electrostatic interactions
Summary
Protein detection in biological samples has received considerable attention in disease diagnosis, food safety control, environmental monitoring and many other fields. The magnetic nanoprobes strategy developed recently has proven to be a highly sensitive technique for detecting human tumor cells, and is especially well suited to separate and in the meantime detect low-concentrations of proteins [20,21] Another important issue in electrochemical immunosensors is converting the specific antibody-antigen interaction to a detectable electrochemical signal so as to quantitatively determine the concentration of target antigen. With a view to overcome the challenge for developing a label-free, simple, fast, nontoxic and reproducible assay system, a novel electrochemical immunosensor for tumor biomarkers has been demonstrated by co-immobilizing target-specific aptamer and electron mediator on magnetic nanoprobes. The method combined the following advantages: (1) Hemin and anti-AFP co-immobilized on magnetic nanoprobes and the detection of AFP was realized through a one-step immunoassay format that could bring in a simple, label-free and sensitive sensor design.
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