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In this experiment, a Cu 2 O spherical nanoparticle was reduced by hydrothermal reaction to prepare a label-free electrochemical immunosensor based on a novel signal amplification strategy. Multi-walled carbon nanotubes are a platform that combines cuprous oxide with carbon nanotubes. Nanogold was modified on the surface of cuprous oxide nanospheres by electrostatic adsorption to further amplify the electrochemical signal and link-supported anti-alpha-fetoprotein (AFP). Under optimal conditions, the proposed immunosensor has a wide linear range from 0.001 to 40 ng/ml, with a detection limit as low as 0.33 pg/ml ( S / N = 3). Furthermore, the proposed label-free immunosensor has been used to determine AFP in human serum with satisfactory results. At the same time, it has good reproducibility, acceptable selectivity and long-term stability, and has broad application prospects in biometric analysis.

In this work, a novel electrochemical immunosensor was designed for ultrasensitive determination of carcinoembryonic antigen based on 3D-structured rGO/Ag-Au NPs. 3D-rGO-MWCNTs nanocomposites feature network structure which has a large specific surface area and excellent conductivity providing more active sites for Ag-Au bimetallic nanoparticles. At the same time, the synergistic effect of 3D-rGO-MWCNTs and Ag-Au NPs, significantly improved the electrochemical performance of the modified electrode. Due to the excellent biocompatibility of Ag-Au NPs, the antibody could be well attached to the electrode, and the immunosensor could be successfully prepared. Under the optimized conditions, the constructed immunosensor showed a wide linear range from 0.001 ng mL−1 to 80 ng mL−1 with the detection limit of 3 pg mL−1 (S/N ratio of 3). The proposed immunosensor has excellent analytical performance including good stability, reproducibility and selectivity, and was successfully applied to the detection of CEA in human serum verified its practicability.

In this study, a novel signal-amplified immunosensor was designed by using a microwave-assisted self-assembly method to synthesize ZnFe

A three-dimensional array of reduced graphene oxide/MoS2 @ polyaniline-layered nanosheets (denoted as rGO/MoS2 @ PANI) has a novel structure of intercalated MoS2/PANI nanosheets arrays arranged on rGO that can be used as carcinoembryonic antigen (CEA) electrochemical immunosensors (detectors). In this graded nanosheet, the PANI was embedded in the MoS2 interlayer. The MoS2/PANI nanosheets themselves limit volumetric changes when arranged as MoS2/PANI nanosheet arrays on rGO nanosheets to provide tight and sufficient heterogeneity. PANI locates on the interface itself and contains a large amount of –NH2 that can bind many antibodies. Simultaneously, we investigated the optimal amount of aniline to add. We found that these arrays had excellent film thickness and conductivity for improving CEA detection sensitivity. The tested immunosensor achieved sensitive and specific detection of CEA, with a detection limit of 0.3 pg mL−1. Under the optimal conditions, the prepared immunosensor exhibited acceptable reproducibility and selectivity and excellent stability. Satisfactory results of human serum samples indicated the potential application of the immunosensor for clinical monitoring of tumor markers.

A “label-free” electrochemical immunosensor was developed to detect α-fetoprotein (AFP) sensitively. HCS@PANI (High carbonized nanospheres@Polyaniline) is used as an electrochemical sensing platform to improve conductivity and enhanche the amount of AFP antibody (anti-AFP) immobilized on the electrode surface. PANI, which is involved by protonic acid, exhibits excellent electrochemical activity and can be used as a direct electron mediator to further amplify electrochemical signals. Under optimal conditions, the electrochemical immunosensor has a linear range of 0.001–80 ng/mL and a minimum detection limit of 0.33 pg/mL. The immunosensor is expected to be used in clinical laboratories to detect AFP and other tumor markers in human plasma for precancerous screening or cancer surveillance.

In this study, a novel signal-amplified immunosensor was designed by using a microwave-assisted self-assembly method to synthesize ZnFe2O4-Ag/rGO nanocomposites. The conductivity of ZnFe2O4-rGO nanocomposites was significantly improved due to the effective inhibition of rGO accumulation by the insertion of ZnFe2O4 and Ag nanoparticles (NPs) into graphene sheets. Excellent sensitivity and reproducibility were achieved through the microwave-assisted preparation of ZnFe2O4-Ag/rGO nanocomposites as a substrate, with the Ag NPs enhancing the signal because of the effective conductive matrix. The layer assembly process of the immunosensor was verified by cyclic voltammetry and electrochemical impedance spectroscopy. Under optimal conditions, the fabricated immunosensor showed good linearity over a wide concentration range from 1 pg mL−1 to 200 ng mL−1 with a low detection limit of 0.98 pg mL−1, and exhibited excellent specificity, good stability, and reproducibility. These qualities can contribute to the successful application of a label-free immunosensor in the detection of AFP in human serum.

An electrochemical immunosensor for quantitation of carcinoembryonic antigen (CEA) based on Au-Ag/rGO@PDA nanocomposites for dual signal amplification strategy was designed. Polydopamine-coated Ag/graphene hybrids were synthesized by one-step reduction and functionalization, and the dopamine was introduced to replace some reducing agents that are harmful to organisms. Silver nanoparticles modified on the electrodes produced sensitive electrochemical redox peaks. When different amounts of protein (antigen, antibody, bovine serum protein, etc.) were adsorbed on the surface of nano-silver, the surface of nano-silver was covered. The electrochemical redox peak of silver particles decreased due to the change of the effective area of bare silver particles which could react with electrodes. In addition, CEA-antibody (anti-CEA) was immobilized into a biocompatible nanocomposite of Au nanoparticles as a conductive matrix, and CEA-antibody (anti-CEA) was combined with Ag/rGO@PDA to form a dual signal amplifying element. Under optimal condition, the linear relationship was obtained from 0.001 ng mL−1 to 80 ng mL−1 between current signal and CEA concentration with a detection limit of 0.286 pg mL−1 (signal-to-noise ratio is 3). The label-free electrochemical immunosensor has been successfully applied to human serum detection due to good selectivity, stability and reproducibility.