Highly sensitive luminol electrochemiluminescence immunosensor based on ZnO nanoparticles and glucose oxidase decorated graphene for cancer biomarker detection

In this work, we reported a sandwiched luminol electrochemiluminescence (ECL) immunosensor using ZnO nanoparticles (ZnONPs) and glucose oxidase (GOD) decorated graphene as labels and in situ generated hydrogen peroxide as coreactant. In order to construct the base of the immunosensor, a hybrid architecture of Au nanoparticles and graphene by reduction of HAuCl₄ and graphene oxide (GO) with ascorbic acid was prepared. The resulted hybrid architecture modified electrode provided an excellent platform for immobilization of antibody with good bioactivity and stability. Then, ZnONPs and GOD functionalized graphene labeled secondary antibody was designed for fabricating a novel sandwiched ECL immunosensor. Enhanced sensitivity was obtained by in situ generating hydrogen peroxide with glucose oxidase and the catalysis of ZnONPs to the ECL reaction of luminol–H₂O₂ system. The as-prepared ECL immunosensor exhibited excellent analytical property for the detection of carcinoembryonic antigen (CEA) in the range from 10 pg mL⁻¹ to 80 ng mL⁻¹ and with a detection limit of 3.3 pg mL⁻¹ (S N⁻¹ = 3). The amplification strategy performed good promise for clinical application of screening of cancer biomarkers.     

Magnetic electrochemiluminescent Fe3O4/CdSe-CdS nanoparticle/polyelectrolyte nanocomposite for highly efficient immunosensing of a cancer biomarker

Magnetic electrochemiluminescent Fe₃O₄/CdSe–CdS nanoparticle/polyelectrolyte nanostructures have been synthesized and used to fabricate an electrochemiluminescence (ECL) immunosensor for the detection of carcinoembryonic antigen (CEA). CEA is a protein used as a biomarker for several cancers; particularly, to monitor response to treatment in colon and rectal cancer patients. The nanocomposites can be easily separated and firmly attached to an electrode owing to their excellent magnetic properties. This represents a promising advantage for bioassay applications. More importantly, the nanostructures exhibit intense and stable ECL emissions in neutral solution, which makes them ideal for ECL immunosensing. The 3‐aminopropyltriethoxysilane (APS) polyelectrolyte shell on the nanostructure surface not only enhances the intensity and stability of the ECL signal, but also acts as a crosslinker for immunosensor fabrication. A CEA antibody immobilized onto a nanocomposite/APS/electrode with gold nanoparticles comprises the ECL immunosensor. The principle of ECL detection for CEA is based on a change in steric hindrance after immunoreaction, which leads to a decrease in ECL intensity. A wide detection range (0.064 pg ml^?1–10 ng ml^?1) and low detection limit (0.032 pg ml^?1) are achieved. The immunosensor is highly sensitive and selective, and exhibits excellent stability and good reproducibility. It thus has great potential for clinical protein detection. In particular, this approach uses a novel class of bifunctional nanocomposites that display both intense ECL and excellent magnetism, which renders them suitable for a large range of bioassay applications.     

One step electrochemically deposited nanocomposite film of chitosan-carbon nanotubes-gold nanoparticles for carcinoembryonic antigen immunosensor application

A simple and controllable one-step electrodeposition method for the preparation of a chitosan-carbon nanotubes-gold nanoparticles (CS-CNTs-GNPs) nanocomposite film was used to fabricate an immunosensor for detection of carcinoembryonic antigen (CEA). The porous three-dimensional CS-CNTs-GNPs nanocomposite film, which offered a large specific surface area for immobilization of antibodies, exhibited improved conductivity, high stability and good biocompatibility. The morphology of the formed nanocomposite film was investigated by scanning electron microscopy (SEM), and the electrochemical behaviors of the immunosensor were characterized by electrochemical impedance spectroscopy (EIS) and cyclic voltammetry (CV). Under the optimal conditions, the proposed immunosensor could detect CEA in two linear ranges from 0.1 to 2.0 ng mL⁻¹ and from 2.0 to 200.0 ng mL⁻¹, with a detection limit of 0.04 ng mL⁻¹. The immunosensor based on CS-CNTs-GNPs nanocomposite film as the antibody immobilization matrix could exhibit good sensitivity, stability, and reproducibility for the determination of CEA.     

Development of a non-labeled immunosensor for the herbicide trifluralin via optical waveguide lightmode spectroscopic detection

A highly sensitive immunosensor using optical waveguide lightmode spectroscopy (OWLS) was developed for the detection of the herbicide trifluralin. OWLS as an in situ and label free method of detection, based on the measurement of the diffraction of a linearly polarized laser beam (He-Ne laser, 632.8 nm) on a diffraction grating in a thin waveguide layer (SiO₂-TiO₂), offered means to produce immunosensors utilizing immobilized antibodies raised against trifluralin allowing a non-competitive biosensor, or immobilized trifluralin conjugate allowing a competitive biosensor for this analyte. Immobilization of molecules sensitizing the sensor was undertaken on amino silanized waveguide surfaces in a two-step procedure using glutaraldehyde. Within the immobilized antibody (Ab) based immunosensor the signal measured was proportional to the trifluralin content in the samples, but the method allowed detection of trifluralin only above 100 ng ml⁻¹ due to the small molecular size of the antigen (Ag). In the immobilized antigen based immunosensor, a trifluralin-bovine serum albumin (BSA) conjugate was covalently linked to the waveguide surface. During measurements the standard solutions and samples were mixed in 1:1 ratio with antiserum, containing constant amounts of antibodies. The amount of free antibodies bound to the surface was inversely proportional to the trifluralin content of the solutions measured. The immobilized antigen based method allowed detection of trifluralin in the concentration range of 2×10⁻⁷ to 3×10⁻⁵ ng ml⁻¹. Results of trifluralin determinations were compared to those obtained in parallel enzyme-linked immunosorbent assay (ELISA) tests and in gas chromatorgraphic-mass spectrometric (GC-MS) analyses, and indicated an increase of six orders of magnitude in the limit of detection (LOD).     

An electrochemical immunosensor for carcinoembryonic antigen enhanced by self-assembled nanogold coatings on magnetic particles

A quick and reproducible electrochemical-based immunosensor technique, using magnetic core/shell particles that are coated with self-assembled multilayer of nanogold, has been developed. Magnetic particles that are structured from Au/Fe₃O₄ core-shells were prepared and aminated after a reaction between gold and thiourea, and additional multilayered coatings of gold nanoparticles were assembled on the surface of the core/shell particles. The carcinoembryonic antibody (anti-CEA) was immobilized on the modified magnetic particles, which were then attached on the surface of solid paraffin carbon paste electrode (SPCE) by an external magnetic field. This is an assembly of a novel immuno biosensor for carcinoembryonic antigen (CEA). The sensitivity and response features of this immunoassay are significantly affected by the surface area and the biological compatibility of the multilayered nanogold. The linear range for the detection of CEA was from 0.005 to 50 ng mL⁻¹ and the limit of detection (LOD) was 0.001 ng mL⁻¹. The LOD is approximately 500 times more sensitive than that of the traditional enzyme-linked immunosorbent assay for CEA detection.     

Synthesis of a new biacridine and its use as the chemiluminescent probe for immunoassay of carcinoembryonic antigen

A new biacridine compound, 10,10′-dimethyl-3,3′-disulfo-9,9′-biacridine (DMDSBA) was synthesized, and its chemiluminescent characteristics were investigated in detail. DMDSBA was used to label anti-CEA antibody. The labeling ratio was estimated to be 1.15-1.32, and the average labeling ratio was 1.25. The results show that there are no obvious changes in the immunoreactivity of the labeled anti-CEA antibody and the quantum efficiency of DMDSBA after attaching to the anti-CEA antibody. In addition, the conditions of labeling reaction, sandwich immunoassay and chemiluminescent reaction have been studied. A new sandwich chemiluminescent immunoassay method was firstly established, and used to determine CEA in human serum, the calibration range is 1.0-100 ng ml⁻¹ and the minimal detectable concentration of CEA is 0.53 ng ml⁻¹, the relative standard deviation is 6.5% for 20 ng ml⁻¹ CEA. This method was well-matched with radio immunoassay.     

Electrochemical immunosensor for carcinoembryonic antigen based on antigen immobilization in gold nanoparticles modified chitosan membrane.

A disposable electrochemical immunosensor for carcinoembryonic antigen (CEA) was proposed based on the antigen immobilized in a colloidal gold nanoparticles modified chitosan membrane on the surface of an indium-tin oxide (ITO) electrode. The different membranes were characterized by scanning electron microscope and electrochemical methods. Based on a competitive immunoassay format, the immobilized antigen of the immunosensor was incubated with a horseradish peroxidase (HRP) labeled antibody and sample CEA antigen, and the formed immunoconjugate in the immunosensor was detected by an o-phenylenediamine-H(2)O(2)-HRP electrochemical system. Under the optimal experimental conditions, the electrocatalytic current decreased linearly with the competitive mechanism. CEA could be determined in the linear range from 2.0 to 20 ng/ml with a detection limit of 1.0 ng/ml. The prepared CEA immunosensor is not only economic due to the low-cost ITO electrode obtained from industrial mass production, but is also capable with good stability and reproducibility for batch fabrication.     

磁性无机-生物复合粒子敏感膜新型电流型免疫传感器的研究

合成了磁性Fe3O4纳米粒子,利用3-氨基丙基三乙氧基硅烷(APS)进行硅烷化,形成表面带有氨基的磁性Fe3O4纳米复合粒子,再用戊二醛将羊抗人免疫球蛋白G抗体(anti-IgG)固定在该磁性粒子表面,通过磁力将其修饰于固体石蜡碳糊电极表面制作成免疫传感器。与标记HRP的二抗体anti-IgG结合,以对苯二酚作为电子媒介体,实现对人免疫球蛋白G(IgG)的定量检测。IgG测定线性范围为2.5~400μg/L,检出限为0.75μg/L。该免疫传感器制作简单,成本低,表面更新方便,可用于临床血清检测。     

Simultaneous detection of four biomarkers with one sensing surface based on redox probe tagging strategy

In this paper, a simple and sensitive amperometric immunosensor for simultaneous detection of four biomarkers by using distinguishable redox-probes as signal tags was proposed for the first time. In sandwich immunoassay format, four kinds of capture antibodies (C-Ab) were immobilized by gold nanoparticles (AuNPs) electro-deposited on the surface of glass carbon electrode (GCE); four kinds of detection antibodies (D-Ab) labeled with different redox probes (including anthraquinone 2-carboxylic acid (Aq), thionine (Thi), ferrocenecarboxylic acid (Fc) and tris(2,2’-bipyridine-4,4’-dicarboxylic acid) cobalt(III) (Co(bpy)₃³⁺)), were combined with 3,4,9,10-perylenetetracarboxylic acid (PTCA), poly(diallyldimethylammonium chloride) (PDDA) and AuNPs functionalized carbon nanotubes, and served as signal tracer. When four target antigens were present, differential pulse voltammetry (DPV) scan exhibited four well-resolved peaks, each peak indicated one antigen, and its intensity was quantitative correlational to the concentration of corresponding analyte. To verify the strategy, four biomarkers for diagnosis of colorectal carcinoma, including carcinoembryonic antigen (CEA), carbohydrate antigen (CA) 19-9 CA125, and CA242, were used as model analytes, the immunosensor exhibited high selectivity and sensitivity, and peak current displayed good linear relationship to logarithm concentration in the ranges from 0.016 to 15 ng mL⁻¹ for CEA; 0.008 to 10 ng mL⁻¹ for CA19-9; 0.012 to 12 ng mL⁻¹ for CA125; 0.010 to 10 ng mL⁻¹ for CA242, and low detection limits of 4.2, 2.8, 3.3 and 3.8 pg mL⁻¹, respectively.     

Nanosilver-doped DNA polyion complex membrane for electrochemical immunoassay of carcinoembryonic antigen using nanogold-labeled secondary antibodies

A simple and sensitive electrochemical immunoassay protocol was developed for the detection of carcinoembryonic antigen (CEA) using nanosilver-doped DNA polyion complex membrane (PIC) as sensing interface. To construct such an immunosensor, double-stranded DNA was initially assembled onto the surface of thionine/Nafion-modified screen-printed carbon electrode to adsorb silver ions with positive charges, then silver ions were reduced to nanosilver particles with the aid of NaBH₄, and then anti-CEA antibodies were immobilized on the nanosilver surface. Gold nanoparticles conjugated with horseradish peroxidase-labeled anti-CEA were employed as signal antibodies for the detection of CEA with a sandwich-type assay format. Under optimal conditions, the immunosensor exhibited a dynamic range of 0.03-32 ng mL⁻¹ with a low detection limit of 10 pg mL⁻¹ CEA. Intra- and inter-assay imprecision (CVs) were <9.5% and 6.5%, respectively. The response could remain 90.1% of the original current at 30th day. 50 real samples were evaluated using the immunosensor and the enzyme-linked immunosorbent assay, respectively, and received in accordance with those two methods.     

Chitosan–iron oxide nanobiocomposite based immunosensor for ochratoxin-A

The rabbit immunoglobulin antibodies (IgGs) have been immobilized onto nanobiocomposite film of chitosan (CH)–iron oxide (Fe₃O₄₎ nanoparticles prepared onto indium–tin oxide (ITO) electrode for detection of ochratoxin-A (OTA). Excellent film forming ability and availability of –NH₂ group in CH and affinity of surface charged Fe₃O₄ nanoparticles for oxygen support the immobilization of IgGs. Differential pulse voltammettry (DPV) studies indicate that Fe₃O₄ nanoparticles provide increased electroactive surface area for loading of IgGs and improved electron transport between IgGs and electrode. IgGs/CH–Fe₃O₄ nanobiocomposite/ITO immunoelectrode exhibits improved characteristics such as low detection limit (0.5 ng dL⁻¹), fast response time (18 s) and high sensitivity (36 μA/ng dL⁻¹ cm⁻²) with respect to IgGs/CH/ITO immunoelectrode.     

One‐Step Electrochemical Immunoassay for Carcinoembryonic Antigen in Human via Back‐Filling Immobilization of Gold Nanoparticles on DNA‐Modified Gold Electrodes

A new amperometric immunobiosensor for carcinoembryonic antigen (CEA) determination in human serum was developed via encapsulation of horseradish peroxidase‐labeled carcinoembryonic antibody (HRP‐anti‐CEA) in a gold nanoparticles/DNA composite architecture. The presences of gold nanoparticles provided a congenial microenvironment for the immobilized biomolecules and decreased the electron transfer impedance, leading to a direct electrochemical behavior of the immobilized HRP. The formation of the antibody–antigen complex by a simple one‐step immunoreaction between the immobilized HRP‐anti‐CEA and CEA in sample solution introduced a barrier of direct electrical communication between the immobilized HRP and the gold electrode surface. Under optimal conditions, the current change obtained from the labeled HRP relative to H₂O₂ system was proportional to the CEA concentration in two linear ranges from 0.5 to 15 ng/mL and 15 to 300 ng/mL with a detection limit of 0.1 ng/mL (at 3δ). The precision and reproducibility are acceptable with the intraassay CV of 6.3% and 4.7% at 8 and 60 ng/mL CEA, respectively. The storage stability of the proposed immunosensor is acceptable in a pH 7.0 PBS at 4 °C for 9 days. Moreover, the proposed immunosensors were used to analyze CEA in human serum specimens. Analytical results of clinical samples show the developed immunoassay has a promising alternative approach for detecting CEA in the clinical diagnosis.     

Quantum dots based electrochemiluminescent immunosensor by coupling enzymatic amplification for ultrasensitive detection of clenbuterol

An ultrasensitive electrochemiluminescence (ECL) immunosensor based on CdSe quantum dots (QDs) has been designed for the detection of clenbuterol. The immunosensor was fabricated by layer by layer and characterized with atomic force microscopic images (AFM) and electrochemical impedance spectra (EIS). In oxygen-saturated pH = 9.0 Tris-HCl buffer, a strong ECL emission of QDs could be observed during the cathodic process due to the H₂O₂ product from electrochemical reduction of dissolved oxygen. Upon the formation of immunocomplex, the second antibody labeled with horseradish peroxidase was simply immobilized on the electrode surface. The ECL emission decreased since steric hindrance of the immunocomplex slowed down the electron-transfer speed of dissolved oxygen, and also could be greatly amplified by an enzymatic cycle to consume the self-produced coreactant. Using clenbuterol as model analyte, the ECL intensity was determined by the concentration of competitive immunoassay of clenbuterol with a wide calibration in the range of 0.05 ng mL⁻¹ to 1000 ng mL⁻¹, and a low detection limit was 0.02 ng mL⁻¹. The immunosensor shows good stability and fabrication reproducibility. It was applied to detecting practical samples with the satisfactory results. This immunosensing strategy opens a new avenue for detection of residue and application of QDs in ECL biosensing.     

An electrochemical biosensor for α-fetoprotein based on carbon paste electrode constructed of room temperature ionic liquid and gold nanoparticles

A novel and effective electrochemical immunosensor for the rapid determination of α-fetoprotein (AFP) based on carbon paste electrode (CPE) consisting of room temperature ionic liquid (RTIL) N-butylpyridinium hexafluorophosphate (BPPF₆) and graphite. The surface of the CPE was modified with gold nanoparticles for the immobilization of the α-fetoprotein antibody (anti-AFP). By sandwiching the antigen between anti-AFP on the CPE modified with gold nanoparticles and the secondary antibody, polyclonal anti-human-AFP labeled with horseradish peroxidase (HRP-labeled anti-AFP), the immunoassay was established. The concentration of AFP was determined based on differential pulse voltammetry (DPV) signal, which was generated in the reaction between O-aminophenol (OAP) and H₂O₂ catalyzed by HRP labeled on the sandwich immunosensor. AFP concentration could be measured in a linear range of 0.50-80.00 ng mL⁻¹ with a detection limit of 0.25 ng mL⁻¹. The immunosensor exhibited high sensitivity and good stability, and would be valuable for clinical assay of AFP.     

A rapid and highly sensitive portable chemiluminescent immunosensor of carcinoembryonic antigen based on immunomagnetic separation in human serum

To detect a biomarker for lung cancer, carcinoembryonic antigen (CEA), a highly sensitive, selective, rapid and portable immunosensor based on immunomagnetic separation and chemiluminescence immunoassay was introduced. A sandwich scheme assay has been utilized with horseradish peroxidase (HRP) labeled anti-CEA antibody and immunomagnetic beads (IMBs). The presence of target protein CEA caused the formation of the sandwich structures (IMBs-CEA-HRP labeled antibody). IMBs were applied to capture CEA and immobilize CEA through the external magnetic field. The HRP at the surface of the antibody catalytically oxidized the luminescence substrate to generate optical signals which were detected by a portable home-made luminometer and which were directly proportional to the concentration of CEA in the samples. The signals were dependent on CEA concentrations in a linear range from 0 to 50 ng mL⁻¹. The limit of detection (LOD) of this method was as low as 5.0 pg mL⁻¹ (S/N = 3). The novel immunosensor was highly sensitive with an assay time of <35 min. The intra- and inter-assay coefficients of variation were <10%. The anti-CEA antibody can be bound to the bead efficiently with a conjugation rate of 73%. IMBs could be stored in 4 °C protecting from light for 2 months without obvious reduction of biological activity. Human reference sera mixed with various concentrations of CEA were tested with the proposed method and commercial enzyme-linked immunosorbent assay (ELISA) kit, and a good linear relationship was obtained. This proposed technique demonstrated an excellent performance for quantifying CEA and was expected to be used for clinical testing.     

An electrochemical immunosensor based on enzyme-encapsulated liposomes and biocatalytic metal deposition

A novel electrochemical immunosensor based on double signal amplification of enzyme-encapsulated liposomes and biocatalytic metal deposition was developed for the detection of human prostate specific antigen (PSA). Alkaline phosphatase (ALP)-encapsulated and detection antibody-functionalized liposomes were first prepared and used as the detection reagent. In the sandwich immunoassay, the model analyte PSA was first captured by anti-PSA capture antibody immobilized on the electrode and then sandwiched with the functionalized liposomes. The bound liposomes were then lysed with surfactant to release the encapsulated ALP, which served as secondary signal amplification means. ALP on the electrode surface initiated the hydrolysis of ascorbic acid 2-phosphate (AA-p) to produce ascorbic acid. The latter, in turn, reduced silver ions on the electrode surface, leading to deposition of the metal silver on the electrode surface. Linear sweep voltammetry (LSV) was chosen to detect the amount of the deposited silver. The results showed that the anodic stripping peak current was linearly dependent on the PSA concentration in the range of 0.01-100 ng mL⁻¹, and a detection limit as low as 0.007 ng mL⁻¹ can be obtained. Since the cut-off value of human PSA is 4 ng mL⁻¹, the proposed electrochemical immunosensor would be expected to gain widespread applications for the detection of PSA in clinical diagnosis.     

Amperometric carbohydrate antigen 19-9 immunosensor based on three dimensional ordered macroporous magnetic Au film coupling direct electrochemistry of horseradish peroxidase

A sandwich-type electrochemical immunosensor for the detection of carbohydrate antigen 19-9 (CA 19-9) antigen based on the immobilization of primary antibody (Ab₁) on three dimensional ordered macroporous magnetic (3DOMM) electrode, and the direct electrochemistry of horseradish peroxidase (HRP) that was used as both the label of secondary antibody (Ab₂) and the blocking reagent. The 3DOMM electrode was fabricated by introducing core–shell Au–SiO₂@Fe₃O₄ nanospheres onto the surface of three dimensional ordered macroporous (3DOM) Au electrode via the application of an external magnet. Au nanoparticles functionalized SBA-15 (Au@SBA-15) was conjugated to the HRP labeled secondary antibody (HRP-Ab₂) through the Au–SH or Au–NH₃⁺ interaction, and HRP was also used as the block reagent. The formation of antigen–antibody complex made the combination of Au@SBA-15 and 3DOMM exhibit remarkable synergistic effects for accelerating direct electron transfer (DET) between HRP and the electrode. Under the optimal conditions, the DET current signal increased proportionally to CA 19-9 concentration in the range of 0.05 to 15.65 U mL⁻¹ with a detection limit of 0.01 U mL⁻¹. Moreover, the immunosensor showed high selectivity, good stability, satisfactory reproducibility and regeneration. Importantly, the developed method was used to assay clinical serum specimens, achieving a good relation with those obtained from the commercialized electrochemiluminescent method.     

Highly-sensitive label-free electrochemical carcinoembryonic antigen immunosensor based on a novel Au nanoparticles–graphene–chitosan nanocomposite cryogel electrode

For the first time, a simple and highly sensitive label-free electrochemical carcinoembryonic antigen (CEA) immunosensor based on a cryogel electrode has been developed and tested. The as-prepared nanocomposite combined the advantages of the graphene, AuNPs and chitosan (AuNPs–GP–CS) together with the ease of preparing a cryogel coupled to a silver deposition, to act as a redox mediator, on a Au electrode. Under the optimal conditions, the decrease of the cyclic voltammetry (CV) silver peak current was proportional to the CEA concentration over a range of from 1.0 × 10⁻⁶ to 1.0 ng mL⁻¹ with a detection limit of 2.0 × 10⁻⁷ ng mL⁻¹. This AuNPs–GP–CS cryogel electrode gave a 1.7 times higher sensitivity and 25 times lower detection limit than the non-cryogel electrode. Moreover, the proposed electrochemical immunosensor exhibited good selectivity, reproducibility and stability. When applied to analyse clinical serum samples, the data determined by the developed immunosensor were in agreement with those obtained by the current hospital analysis system (enzyme linked fluorescent assay) (P > 0.05), to indicate that the immunosensor would be potentially useful for clinical diagnostics.     

Surface plasmon resonance aided electrochemical immunosensor for CK-MB determination in undiluted serum samples

This article presents a simple chronoamperometric immunosensor for the quantitative assessment of creatine kinase MB (CK-MB) in 50 μL undiluted serum samples. The immunosensor consists of gold working and counter electrodes patterned onto a glass chip by thin-film photolithography and an external Ag|AgCl reference electrode. The detection limit (DL) of the chronoamperometric method is 13 ng mL⁻¹ (DL = 2×RMSD/S, where RMSD is the residual mean standard deviation of the measured points around a calibration curve with a slope of S). In spiked serum samples, the response was linear up to 300 ng mL⁻¹ of CK-MB. A surface plasmon resonance (SPR) system with simultaneous electrochemical detection (EC-SPR) aided the development of the sandwich immunoassay. Real-time monitoring of the SPR signal was used to optimize the capture antibody immobilization, CK-MB and detection antibody binding, as well as to minimize the nonspecific adsorption of serum proteins to the sensor surface. The detection antibody has been labeled with alkaline phosphatase (ALP) enzyme for sensitive electrochemical detection. ALP catalyzes the hydrolysis of ascorbic acid phosphate and generates ascorbic acid, which is measured chronoamperometrically. The electrochemical immunoassay for CK-MB was less sensitive to nonspecific adsorption related interferences, had a better detection limit, and required a lower volume of sample than the SPR method.     

A novel antibody–antigen based impedimetric immunosensor for low level detection of HER2 in serum samples of breast cancer patients via modification of a gold nanoparticles decorated multiwall carbon nanotube-ionic liquid electrode

A highly sensitive impedimetric immunosensor based on a gold nanoparticles/multiwall carbon nanotube-ionic liquid electrode (AuNPs/MW-CILE) was developed for the determination of human epidermal growth factor receptor 2 (HER2). Gold nanoparticles were used to enhance the extent of immobilization and to retain the immunoactivity of the antibody Herceptin on the electrode. Cyclic voltammetry and electrochemical impedance spectroscopy were employed for characterization of various layers coated onto the AuNPs/MW-CILE. The impedance measurements at different steps were based on the charge transfer kinetics of the [Fe(CN)₆]^3−/4− redox pair. The immobilization of antibody and the corresponding antigen–antibody interaction at the electrode surface altered the interfacial electron transfer. The interactions of antibody with various concentrations of antigen were also monitored via the change of impedance response. The results showed that the charge transfer resistance increases linearly with increasing concentrations of HER2 antigen. The linear range and limit of detection were found as 10–110 ng mL⁻¹ and 7.4 ng mL⁻¹, respectively. The sensitivity and specificity of the immunosensor were validated. The results showed that the prepared immunosensor is a useful tool for screening of trace amounts of HER2 in serum samples of breast cancer patients.