Xuehui Pang

Ultrasensitive electrochemical immunoassay for CEA through host-guest interaction of β-cyclodextrin functionalized graphene and Cu@Ag core-shell nanoparticles with adamantine-modified antibody.

A novel non-enzymatic immunoassay was designed for ultrasensitive electrochemical detection of carcino-embryonic antigen (CEA) using β-cyclodextrin functionalized Cu@Ag (Cu@Ag-CD) core-shell nanoparticles as labels and β-cyclodextrin functionalized graphene nanosheet (CD-GN) as sensor platform. CD-GN has excellent conductivity which promoted the electric transmission between base solution and electrode surface and enhanced sensitivity of immunosensor. In addition, owing to supramolecular recognition of CD-GN for the guest molecule, quite a few synthesized adamantine-modified primary antibodies (ADA-Ab1) were immobilized on the CD-GN by supramolecular host-guest interaction between CD and ADA. Cu@Ag-CD as a signal tag could be captured by ADA-modified secondary antibody (ADA-Ab2) through a host-guest interaction, leading to a large loading of Cu@Ag nanoparticles with high electrical conductivity and catalytic activity. The fabricated immunosensor exhibits excellent analytical performance for the measurement of CEA with wide range linear (0.0001-20 ng/mL), low detection limit (20 fg/mL), good sensitivity, reproducibility and stability, which provide an enormous application prospect in clinical diagnostics.

Visible light photoelectrochemical aptasensor for adenosine detection based on CdS/PPy/g-C3N4 nanocomposites

In this work, a label-free photoelectrochemical (PEC) aptasensor was developed for adenosine detection based on CdS/PPy/g-C3N4 nanocomposites. The CdS/g-C3N4 heterojunction effectively prevented the photogenerated charges recombination of g-C3N4 and self-photocorrosion processes of CdS, improving photo-to-current conversion efficiency. The introduced polypyrrole (PPy) nanoparticles could lead to a more effective separation of photogenerated charges, thus resulting in a further increasing of photocurrent. The CdS/PPy/g-C3N4 was firstly employed as the photoactive materials for fabrication of aptasensor, and SH-aptamer was then adsorbed on the CdS/PPy/g-C3N4 modified electrodes through S-Cd bond. With increasing of adenosine concentration, the photocurrent decreased as the formation of SH-aptamer-adenosine bioaffinity complexes. Under optimal conditions, the PEC aptasensor had a sensitive response to adenosine in a linear range of 0.3nmolL(-1) to 200nmolL(-1) with a detection limit of 0.1nmolL(-1). Besides, the as-proposed aptasensor has also been applied in human serum samples analysis. The aptasensor exhibits high sensitivity and good stability, thus opening up a new promising PEC platform for some other small molecules analysis.

Application of Europium Multiwalled Carbon Nanotubes as Novel Luminophores in an Electrochemiluminescent Aptasensor for Thrombin Using Multiple Amplification Strategies

A novel electrochemiluminescent (ECL) aptasensor was proposed for the determination of thrombin (TB) using exonuclease-catalyzed target recycling and hybridization chain reaction (HCR) to amplify the signal. The capture probe was immobilized on an Au-GS-modified electrode through a Au-S bond. Subsequently, the hybrid between the capture probe and the complementary thrombin binding aptamer (TBA) was aimed at obtaining double-stranded DNA (dsDNA). The interaction between TB and its aptamer led to the dissociation of dsDNA because TB has a higher affinity to TBA than the complementary strands. In the presence of exonuclease, aptamer was selectively digested and TB could be released for target recycling. Extended dsDNA was formed through HCR of the capture probe and two hairpin DNA strands (NH2-DNA1 and NH2-DNA1). Then, numerous europium multiwalled carbon nanotubes (Eu-MWCNTs) could be introduced through amidation reaction between NH2-terminated DNA strands and carboxyl groups on the Eu-MWCNTs, resulting in an increased ECL signal. The multiple amplification strategies, including the amplification of analyte recycling and HCR, and high ECL efficiency of Eu-MWCNTs lead to a wide linear range (1.0×10(-12)-5.0×10(-9) mol/L) and a low detection limit (0.23 pmol/L). The method was applied to serum sample analysis with satisfactory results.

Label-Free Electrochemiluminescent Immunosensor for Detection of Carcinoembryonic Antigen Based on Nanocomposites of GO/MWCNTs-COOH/Au@CeO2

A high-sensitivity electrochemiluminescence (ECL) sensor was conducted to detect carcinoembryonic antigen (CEA). Nanocomposites of graphene oxide/carboxylated multiwall carbon nanotubes/gold/cerium oxide nanoparticles (GO/MWCNTs-COOH/Au@CeO2) were used as antibody carriers and sensing platforms to modify on glassy carbon electrodes (GCE). CeO2 nanoparticles were first exploited as an ECL luminescent material and the possible ECL mechanism was proposed in this work. GO/MWCNTs-COOH was used as a loading matrix for CeO2 nanoparticles because of the superior conductivity and large specific surface area. Au nanoparticles were further deposited on this matrix to attach anti-CEA and enhance the sensitivity of immunosensor. The proposed sensing platform showed excellent cathodic ECL performance and sensitive response to CEA. The effects of experimental conditions on the ECL performance were investigated. The proposed immunosensor showed the broad linear range (0.05-100 ng/mL) and the low detection limit (LOD, 0.02 ng/mL, signal-to-noise ratio = 3) according to the selected experimental conditions. The excellent analysis performance for determination of CEA in the human serum samples simplied this immunosensor displayed high sensitivity and excellent repeatability. More importantly, this conducted immunosensor broadens the use scope of CeO2 nanoparticles.

A label-free amperometric immunosensor for detection of zearalenone based on trimetallic Au-core/AgPt-shell nanorattles and mesoporous carbon.

A novel label-free amperometric immunosensor is proposed for the ultrasensitive detection of zearalenone (ZEN) based on mesoporous carbon (MC) and trimetallic nanorattles (core/shell particles with movable cores encapsulated in the shells). The nanorattles are composed of special Au-core and imperfect AgPt-shell structure (Au@AgPt). The Au@AgPt nanorattles are loaded onto the MC by physical adsorption. The structure of the Au@AgPt nanorattles was characterized by using scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Energy dispersive X-ray spectroscopy (EDS) confirmed the composition of the synthesized nanorattles. Compared with monometallic and bimetallic nanoparticles (NPs), Au@AgPt nanorattles show a higher electron transfer rate due to the synergistic effect of the Au, Ag and Pt NPs. MC further improves the sensitivity of the immunosensor because of its extraordinarily large specific surface area, suitable pore arrangement and outstanding conductivity. The large specific surface area of MC and MC@Au@AgPt were characterized by the BET method. ZEN antibodies are immobilized onto the nanorattles via Ag-NH2 bonds and Pt-NH2 bonds. Cyclic voltammetry and square wave voltammetry were used to characterize the recognizability of ZEN. Under optimum experimental conditions, the proposed immunosensor exhibited a low detection limit (1.7 pg mL(-1)), a wide linear range (from 0.005 to 15 ng mL(-1)) as well as good stability, reproducibility and selectivity. The sensor can be used in clinical analysis.

Novel signal amplification strategy for ultrasensitive sandwich-type electrochemical immunosensor employing Pd–Fe3O4-GS as the matrix and SiO2 as the label

An ultrasensitive sandwich-type electrochemical immunosensor based on a novel signal amplification strategy was developed for the quantitative determination of human immunoglobulin G (IgG). Pd nanocubes functionalized magnetic graphene sheet (Pd-Fe3O4-GS) was employed as the matrix to immobilize the primary antibodies (Ab1). Owing to the synergetic effect between Pd nanocubes and magnetic graphene sheet (Fe3O4-GS), Pd-Fe3O4-GS can provide an obviously increasing electrochemical signal by electrochemical catalysis towards hydrogen peroxide (H2O2). Silicon dioxide (SiO2) was functionalized as the label to conjugate with the secondary antibodies (Ab2). Due to the larger steric hindrance of the obtained conjugate (SiO2@Ab2), the sensitive decrease of the electrochemical signal can be achieved after the specific recognition between antibodies and antigens. In this sense, this proposed immunosensor can achieve a high sensitivity, especially in the presence of low concentrations of IgG. Under optimum conditions, the proposed immunosensor offered an ultrasensitive and specific determination of IgG down to 3.2 fg/mL. This immunoassay method would open up a new promising platform to detect various tumor markers at ultralow levels for early diagnoses of different cancers.

Ultrasensitive electrochemical immunosensor for SCCA detection based on ternary Pt/PdCu nanocube anchored on three-dimensional graphene framework for signal amplification

In this study, a novel and ultrasensitive sandwich-type electrochemical immunosensor was designed for the quantitative detection of squamous cell carcinoma antigen (SCCA) based on the β-cyclodextrin functionalized graphene nanosheet (CD-GN) and the ternary hollow Pt/PdCu nanocube anchored on three-dimensional graphene framework (Pt/PdCu-3DGF). CD-GN exhibited high specific surface area and good dispersibility and stability in water, which were beneficial to fix captured antibodies (Ab1) through the supramolecular host-guest interaction between CD and Ab1. The abundant oxygen-containing functional groups on 3DGF provided binding sites for anchoring noble metal nanoparticles. Pt/PdCu-3DGF could capture detected antibodies via the interaction of Pd-NH2 and Pt-NH2. Furthermore, the ternary metal nanoparticles exhibited high electrocatalytic activity toward the reduction of hydrogen peroxide. Under optimal conditions, the fabricated immunosensor showed a sensitive response to SCCA with two linear ranges. The linear ranges are 0.0001-1 ng/mL and 1-30 ng/mL with a detection limit of 25 fg/mL. Additionally, the proposed immunosensor showed good reproducibility and stability.

Quenched electrochemiluminescence of Ag nanoparticles functionalized g-C3N4 by ferrocene for highly sensitive immunosensing

In this paper, a novel sandwich electrochemiluminescence (ECL) immunosensor was constructed by ferrocene for quenching Ag nanoparticles functionalized g-C3N4 (Ag@g-C3N4) emission. The prepared Ag@g-C3N4 had strong and stable ECL signals compared to pure g-C3N4 and primary antibody (Ab1) can be immobilized on Ag@g-C3N4 by adsorption of Ag nanoparticles. Ferrocene carboxylic acid (Fc-COOH) labeled secondary antibody was immobilized on Au doped mesoporous Al2O3 nanorods (Au@Al2O3-Fc-COOH@Ab2) as labels through adsorption ability of Au toward proteins. After a sandwich-type immunoreaction, a remarkable decrease of ECL signal was observed due to the ECL quenching of Ag@g-C3N4 by Au@Al2O3-Fc-COOH@Ab2. As a result, the change of ECL intensity has a direct relationship with the logarithm of CEA concentrations in the range of 1 pg mL(-1)-100 ng mL(-1) with a detection limit of 0.35 pg mL(-1) (S/N=3). Additionally, the proposed immunosensor shows high specificity, good reproducibility, and long-term stability.

A novel electrochemiluminescent immunosensor based on the quenching effect of aminated graphene on nitrogen-doped carbon quantum dots.

Nitrogen-doped carbon quantum dots (N-CQDs) with an average diameter of 2 nm were synthesized by carbonization of diethylene triamine pentacetate acid (DTPA). The simple prepared N-CQDs showed excellent electrochemiluminescence (ECL) property and were used as luminophors to fabricate a sandwich-type ECL immunosensor. Aminated graphene (NH2-G) was also synthesized and used as a label of secondary antibody. The labeled NH2-G could effectively quench the ECL of N-CQDs modified on electrodes due to ECL resonance energy transfer (ERET). Immunological recognition which induced ECL quenching enabled the quantitative determination of biomarkers. Alpha fetoprotein (AFP) was selected as a model analyte to investigate the analytical performance of the proposed immunosensor. Under optimal conditions, a good linear relationship between ECL intensity and the logarithm of AFP concentration was obtained in the range of 0.01-100 ng mL(-1) with the detection limit of 3.3 pg mL(-1). The proposed ECL immunosensor showed good stability, acceptable selectivity and reproducibility.

Electrochemiluminescent immune-modified electrodes based on Ag2Se@CdSe nanoneedles loaded with polypyrrole intercalated graphene for detection of CA72-4.

This work described a new electrochemiluminescence (ECL) immunosensor based on polypyrrole intercalated graphene and Ag2Se@CdSe nanoneedles. The novel nanomaterial Ag2Se@CdSe, with needle-like morphology, was synthesized for the first time. The prepared Ag2Se@CdSe nanoneedles exhibited good luminous performance in the presence of K2S2O8. Polypyrrole intercalated amination graphene with high specific binding sites and excellent electrochemical performance was used as the platform for the sensor. The developed ECL immunosensor was used for the detection of CA72-4 with good linear relation in the range from 10(-4) to 20 U/mL and low detection limit of 2.1 × 10(-5) U/mL (S/N = 3). The developed ECL immunosensor with high sensitivity and spectral selectivity can be used for detection of real samples. Ag2Se@CdSe nanoneedles could be promising candidate emitter for ECL biosensors in the future.