Biomolecule‐Doped Organic/Inorganic Hybrid Nanocomposite Film for Label‐Free Electrochemical Immunoassay of α‐1‐Fetoprotein

A new electrochemical immunosensor for the detection of α‐1‐fetoprotien (AFP) was developed based on AFP antibody (anti‐AFP)‐functionalized organic/inorganic hybrid nanocomposite membrane. To fabricate such a hybrid composite membrane, 3,4,9,10‐perylenetetracarboxylic acid‐bound thionine molecules (PTCTH) were initially doped into titania colloids (TiO₂), and then gold nanoparticles and anti‐AFP were immobilized onto the composite film in turn. Comparison with the electrode fabricated only with thionine not 3,4,9,10‐perylenetetracarboxylic acid, the immunosensor with PTCTH exhibited high sensitivity and fast electron transfer. The presence of gold nanoparticles provided a good microenvironment for the immobilization of biomolecules, enhanced the surface coverage of protein, and improved the sensitivity of the immunosensor. The modified process was characterized by scanning electron microscope (SEM), cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). The surface topography of the membrane was investigated by scanning electron microscopy (SEM). Under optimal conditions, the proposed immunosensor exhibited a wide linear range from 2.5 to 200.0 ng/mL towards AFP with a detection limit of 0.5 ng/mL (S/N=3). The stability, reproducibility and precision of the immunosensor were acceptable. Comparison with the conventional enzyme‐linked immunosorbent assay (ELISA), the present method did not require more labeled procedures and washing steps. Significantly, the detection methodology provides a promising approach for other proteins or biosecurities.     

On‐Off PVC Membrane Based Potentiometric Immunosensor for Label‐Free Detection of Alpha‐Fetoprotein

A poly(vinylchloride) (PVC) membrane based potentiometric immunosensor for the direct detection of alpha‐fetoprotein (AFP) has been developed. First, Au colloid particle was chemisorbed upon amino groups of o‐phenylenediamine, which were dissolved in plasticized PVC membrane. Then alpha‐fetoprotein antibody (anti‐AFP) was immobilized upon the surface of the Au colloid particle to prepare a potentiometric AFP immunosensor. The Au colloid particle modified PVC membrane was characterized by digital photo and transmission electron microscope (TEM). The immunosensor exhibited fast potentiometric response (≤4 min) and showed specific response to AFP in the range of 4.9 to 158.5 ng/mL with a correlation coefficient of 0.9971 and a detection limit of 1.6 ng/mL. The factors influencing the performance of the immunosensor were also studied in detail. Moreover, the proposed method is economical and efficient as well as potentially attractive for clinical immunoassays.     

A Reagentless Amperometric Immunosensor for Alpha‐Fetoprotein Based on Gold Nanoparticles/TiO2 Colloids/Prussian Blue Modified Platinum Electrode

A novel reagentless amperometric immunosensor for the determination of alpha‐fetoprotein (AFP) was prepared by immobilizing TiO₂ colloids on Prussian blue (PB) modified platinum electrode, which yielded a positively charged interface with strong adsorption to deposit gold nanoparticles for immobilization of alpha‐fetoprotein antibody (anti‐AFP). The factors influencing the performance of the proposed immunosensors were studied in detail. Under the optimized conditions, cyclic voltammograms determination of AFP showed a specific response in two concentration ranges from 3.0 to 30.0 ng/mL and from 30.0 to 300.0 ng/mL with a detection limit of 1.0 ng/mL at a signal‐to‐noise ratio of 3. The proposed immunosensor exhibited high selectivity, good reproducibility, long‐term stability (>2 months) and good repeatability.     

A Sensitive Electrochemical Immunosensor for α‐Fetoprotein Detection with Colloidal Gold‐Based Dentritical Enzyme Complex Amplification

A sensitive and specific electrochemical immunosensor was developed with α‐fetoprotein (AFP) as the model analyte by using gold nanoparticle label for enzymatic catalytic amplification. A self‐assembled monolayer membrane of mercaptopropionic acid (MPA) was firstly formed on the electrode surface through gold‐sulfur interaction. Monoclonal mouse anti‐human AFP was covalently immobilized to serve as the capture antibody. In the presence of the target human AFP, gold nanoparticles coated with polyclonal rabbit anti‐human AFP were bound to the electrode via the formation of a sandwiched complex. With the introduction of goat anti‐rabbit IgG conjugated with alkaline phosphatase, the dentritical enzyme complex was formed through selective interaction of the secondary antibodies with the colloidal gold‐based primary antibody at the electrode, thus affording the possibility of signal amplification for AFP detection. Current response arising from the oxidation of enzymatic product was significantly amplified by the dentritical enzyme complex. The current signal was proportional to the concentration of AFP from 1.0 ng mL^?1 to 500 ng mL^?1 with a detection limit of 0.8 ng mL^?1. This system could be extended to detect other target molecules with the corresponding antibody pairs.     

Electrochemical Immunosensor for α‐Fetoprotein Based on Gold Nanoparticles/Graphene‐Prussian Blue

The electrochemical immunosensor for α‐fetoprotein (AFP) was fabricated based on the platform of gold nanoparticles (GNP)/graphene (Gr)‐prussian blue (PB). By electrodeposition, GNP were modified on the surface of the prepared Gr‐PB. The anti‐AFP‐1,1′‐ferrocenedicarboxylic acid (FcDA) as label was directly immobilized on the platform of GNP/Gr‐PB. And after the immunoreactions, the formed complex inhibited the electron transfer and decreased the catalytic current of FcDA toward the reduction of H₂O₂. And in the range of 10–3200 pg·mL^?1, the decreased current is linear with the concentration of AFP, with a detection limit of 3 pg·mL^?1. The developed immunoassay method showed good precision, high sensitivity, acceptable stability and reproducibility, and could be used for the detection of real samples with consistent results in comparison with those obtained by the enzyme linked immunosorbent assay (ELISA) method.     

The Signal‐Enhanced Label‐Free Immunosensor Based on Assembly of Prussian Blue‐SiO2 Nanocomposite for Amperometric Measurement of Neuron‐Specific Enolase

A signal‐enhanced label‐free electrochemical immunosensor was constructed by the employment of Prussian blue doped silica dioxide (PB‐SiO₂) nanocomposite. At first, PB‐SiO₂ nanocomposite which was produced by using a microemulsion method was used to obtain a nanostructural monolayer on a glassy carbon electrode (GCE) surface. Next amino‐functionalized interface were prepared by self‐assembling 3‐aminopropyltriethoxy silane (APTES) on the PB‐SiO₂ nanoparticle surface. Then chitosan stabled gold nanoparticle (CS‐nanoAu) was subsequently attached, while the entire surface was finally loaded with neuron‐specific enolase antibody (anti‐NSE) via the adsorption of gold nanoparticle. The sensitivity of the proposed immunosensor has greatly improved as the PB‐SiO₂ nanostructural sensing film provides plenty of active sites which might catalyze the reduction of H₂O₂. The immunosensor exhibited good linear behavior in the concentration range from 0.25–5.0 and 5.0–75 ng/mL for the quantitative analysis of neuron‐specific enolase (NSE), a putative serum marker of small‐cell lung carcinoma (SCLC), with a limit of detection of 0.08 ng/mL. The resulting NSE immunosensor showed high sensitivity and long‐term lifetime which can be attributed to the extremely high catalytic activity and biocompatibility of CS‐nanoAu/APTES/PB‐SiO₂ nanostructural multilayers.     

Double‐Layer Nanogold and Double‐Strand DNA‐Modified Electrode for Electrochemical Immunoassay of Cancer Antigen 15‐3

Various sensor‐based immunoassay methods have been extensively developed for the detection of cancer antigen 15‐3 (CA 15‐3), but most often exhibit low detection signals and low detection sensitivity, and are unsuitable for routine use. The aim of this work is to develop a simple and sensitive electrochemical immunoassay for CA 15‐3 in human serum by using nanogold and DNA‐modified immunosensors. Prussian blue (PB), as a good mediator, was initially electrodeposited on a gold electrode surface, then double‐layer nanogold particles and double‐strand DNA (dsDNA) with the sandwich‐type architecture were constructed on the PB‐modified surface in turn, and then anti‐CA 15‐3 antibodies were adsorbed onto the surface of nanogold particles. The double‐layer nanogold particles provided a good microenvironment for the immobilization of biomolecules. The presence of dsDNA enhanced the surface coverage of protein, and improved the sensitivity of the immunosensor. The performance and factors influencing the performance of the immunosensor were evaluated. Under optimal conditions, the proposed immunosensor exhibited a wide linear range from 1.0 to 240 ng/mL with a relatively low detection limit of 0.6 ng/mL (S/N=3) towards CA 15‐3. The stability, reproducibility and precision of the as‐prepared immunosensor were acceptable. 57 serum specimens were assayed by the developed immunosensor and standard enzyme‐linked immunosorbent assay (ELISA), respectively, and the results obtained were almost consistent. More importantly, the proposed methodology could be further developed for the immobilization of other proteins and biocompounds.     

A Solid‐State Electrochemiluminescence Immunosensor Based on MWCNTs‐Nafion and Ru(bpy)32+/Nano‐Pt Nanocomposites for Detection of α‐Fetoprotein

A approach was successfully employed for constructing a solid‐state electrochemiluminescence (ECL) immunosensor by layer‐by‐layer self‐assembly of multiwall carbon nanotubes (MWCNTs)‐Nafion composite film, Ru(bpy)₃²⁺/nano‐Pt aggregates (Ru‐PtNPs) and Pt nanoparticles (PtNPs). The influence of Pt nanoparticles on the ECL intensity was quantitatively evaluated by calculating the electroactive surface area of different electrodes with or without PtNPs to immobilize Ru(bpy)₃²⁺. The principle of ECL detection for target α‐fetoprotein antigen (AFP) was based on the increment of resistance after immunoreaction, which led to a decrease in ECL intensity. The linear response range was 0.01–10 ng mL^?1 with the detection limit of 3.3 pg mL^?1. The immunosensor exhibited advantages of simple preparation and operation, high sensitivity and good selectivity.     

FeS2−AuNPs Nanocomposite as Mimicking Enzyme for Constructing Signal‐off Sandwich‐type Electrochemical Immunosensor Based on Electroactive Nickel Hexacyanoferrate as Matrix

In this work, a novel sandwich‐type electrochemical immunosensor with electroactive nickel hexacyanoferrate nanoparticles (NiHCFNPs) as matrix was constructed for α‐fetoprotein (AFP) detection in a signal‐off manner by using FeS₂?AuNPs nanocomposite catalyzed insoluble precipitation to significantly inhibit the electrochemical signal. Initially, the NiHCFNPs with excellent electrochemical property was modified on the electrodeposited nano‐Au electrode to obtain a strong initial electrochemical signal. Subsequently, another nano‐Au layer was formed for immobilization of capture antibody (Ab₁). In the presence of target AFP, the prepared FeS₂?AuNPs‐Ab₂ bioconjugate could be specifically recognized and immobilized on electrode through the sandwich‐type immunoreaction. The FeS₂ with large specific surface areas were used as scaffolds to load abundant mimicking enzyme AuNPs. With the help of hydrogen peroxide (H₂O₂), FeS₂?AuNPs with peroxidase‐like activity accelerated the 4‐chloro‐1‐naphthol (4‐CN) oxidation with generation of insoluble precipitation on electrode, which would greatly hinder the electron transfer and thus caused the decrease of electrochemical signal for quantitative determination of AFP. This approach achieved a wide dynamic linear range from 0.0001 to 100 ng mL^?1 with an ultralow limit detection of 0.028 pg mL^?1. Especially, the proposed AFP immunosensor can be applied to detect human serum samples with satisfactory results, indicating a potential application in clinical monitoring of tumor biomarkers.     

Electro‐nano Diagnostic Platforms for Simultaneous Detection of Multiple Cancer Biomarkers

In this study, a bimetallic nanomaterial‐based electrochemical immunosensor was developed for the detection of carcinoembryonic antigen (CEA) and vascular endothelial growth factor (VEGF) cancer biomarkers at the same time. CEA and VEGF biomarkers are indicators for colon and breast cancers and stomach cancers, respectively. During the study, gold nanoparticle (AuNp), lead nanoparticle (PbNp), copper nanoparticle (CuNp) and magnetic gamma iron(III)oxide (γFe₂O₃ Np) were synthesized, characterized and used together for the first time in the structure of an electrochemical biosensor based on anti‐CEA and anti‐VEGF. For this purpose, Au SPE based sandwich immunosensor was fabricated by using labeled anti‐CEA (labeled with Pb⁺²) and labeled anti‐VEGF (labeled with Cu⁺²). As a result, CEA and VEGF biomarkers were detected following the oxidation peaks of label metals (Pb⁺² and Cu⁺²) by using differential pulse voltammetry. After the experimental parameters were optimized, the linear range was found in the concentration range between 25 ng/mL and 600 ng/mL with the relative standard deviation (RSD) value of (n=3 for 600 ng/mL) 3.33 % and limit of detection (LOD) value of 4.31 ng/mL for CEA biomarker. On the other hand, the linear range was found in the concentration range between 0.2 ng/mL and 12.5 ng/mL with the RSD value of (n=3 for 12.5 ng/mL) 5.31 % and LOD value of 0.014 ng/mL for VEGF biomarker. Lastly, sample application studies for synthetic plasma sample and interference studies with dopamine, ascorbic acid, BSA, cysteine and IgG were carried out.     

Graphene and Nanogold‐Functionalized Immunosensing Interface with Enhanced Sensitivity for One‐Step Electrochemical Immunoassay of Alpha‐Fetoprotein in Human Serum

A new electrochemical immunosensing protocol for sensitive detection of alpha‐fetoprotein (AFP, as a model) in human serum was developed by means of immobilization of horseradish peroxidase‐anti‐AFP conjugates (HRP‐anti‐AFP) onto graphene and nanogold‐functionalized biomimetic interfaces. The low‐toxic and high‐conductive graphene complex provided a large capacity for nanoparticulate immobilization and a facile pathway for electron transfer. With a one‐step immunoassay format, the antigen‐antibody complex was formed between the immobilized HRP‐anti‐AFP on the electrode and AFP in the sample. The formed immunocomplex was coated on the electrode surface, inhibited partly the active center of HRP, and decreased the catalytic reduction of HRP toward the enzyme substrate of H₂O₂. Under optimal conditions, the decrease of reduction currents was proportional to AFP concentration, and the dynamic range was 1.0–10 ng/mL with a relative‐low detection limit (LOD) of 0.7 ng/mL AFP. Intra‐ and inter‐assay coefficients of variation (CVs) were less than 10 %. The assay was evaluated for clinical human serum samples, including 8 (possible) patients with hepatocarcinoma and 3 normal human sera. Correct identification of negative/positive samples and perfect accordance with results from Elecsys 2010 Electrochemiluminescent Automatic Analyzer as a reference was obtained. Importantly, the graphene and nanogold‐based sensor provided a promising platform for the detection of other biocompounds, and could be further applied for development of other potential electrochemical bio/chemosensors.     

A Dendrimer Supported Electrochemical Immunosensor for the Detection of Alpha‐feto protein – a Cancer Biomarker

The electrochemical detection of alpha‐feto protein based on novel gold nanoparticles‐ poly(propylene imine) dendrimer platform is reported. The platform was prepared by co‐electrodeposition of gold nanoparticles and generation 3 poly (propylene imine) dendrimer on a glassy carbon electrode. Each modifying step was characterised by cyclic voltammetry and electrochemical impedance spectroscopy. The electrochemical measurements showed that the platform was stable, conducting and exhibited reversible electrochemistry. Results obtained from the electrochemical impedance spectroscopy interrogation in [Fe(CN)₆^3−/4−] redox probe showed a marked reduction in charge transfer resistance (R_ct) after each modification step. The immunosensor was prepared by immobilisation of a probe anti‐alpha feto protein (AFP) on the platform for 3 hrs at 35 °C followed by blocking the surface with bovine serum albumin to minimise non‐specific binding. The prepared immunosensor was used to detect AFP over a wide concentration range from 0.005 to 500 ng/mL and detection limits of 0.0022 and 0.00185 ng/mL were obtained for SWV and EIS measurements respectively. The immunosensor gave good stability over a period of fourteen days when stored at 4 °C.     

Disposable Amperometric A-fetoprotein Immunosensor Based on the Biocompatible Silk Protein Membranes-Modified Indium Tin Oxide Electrodes

A simple and disposable electrochemical immunosensor for detection of 68 kDa alpha-fetoprotein (AFP) was fabricated based on films of silk fibroin protein membrane (SFPM)/Prussian blue (PB)/deposition of gold nanoparticles (DpAu). First, DpAu and PB were electrochemically deposited successively on the surface of indium tin oxide (ITO) electrode. Then, SFPM with excellent biocompatibility was modified on the surface of PB/DpAu/ITO. The SFPM could form a stable matrix on the electrode surface for the deposition of immunoactive agents. More importantly, the SFPM could prevent the possible leakage of electron mediator and enhance the stability of immunosensor. Scanning electron microscopy (SEM), electrochemical impedance spectroscopy (EIS) and cyclic voltammetry (CV) were used to characterize the assembly process of the modified electrode. The linear range of the proposed immunosensor extended from 1.0 to 200.0 ng/mL for detection of AFP with a detection limit of 0.6 ng/mL. Moreover, the CV test demonstrated the immunosensor exhibited acceptable reproducibility and stability. This composite membrane could be applied for the detection of different biomarkers, diagnosis, and monitoring of carcinoma.

[Supplementary materials are available for this article. Go to the publisher's online edition of Analytical Letters for the following free supplemental resources: additional figures.]     

An Immunosensor for Ultrasensitive Detection of 1‐Pyrenebutyric Acid with Enhanced Electrochemical Performance Based on a Graphene‐Ionic Liquid Doped Chitosan Film Modified Glassy Carbon Electrode

This paper describes a highly sensitive and label‐free electrochemical immunosensor for the detection of 1‐pyrenebutyric acid (PBA) which is based on a graphene (GS), chitosan (CS), and ionic liquid (IL) composite modified glassy carbon electrode (GS‐CS‐IL/GCE). The modification process was monitored by transmission electron microscopy (TEM) and cyclic voltammetry (CV). Due to the synergistic effects of GS, CS, and IL, the biosensor exhibits excellent selectivity to PBA. The current response of the proposed immunosensor decreases linearly at two concentration ranges from 0.01 to 5 and from 5 to 150 ng mL^?1 with a detection limit of 0.01 ng mL^?1.     

GC–MS/MS method for the quantification of α‐cedrene in rat plasma and its pharmacokinetic application

α‐Cedrene is a pharmacologically active ingredient isolated from the essential oil of cedar. A selective and sensitive GC–MS/MS method was developed for the quantification of α‐cedrene in rat plasma for the first time. α‐Cedrene was extracted from rat plasma using ethyl acetate at neutral pH. The analytes were determined in selective reaction monitoring mode using MS/MS: m/z 204.3→119.0 for α‐cedrene and m/z 146.0→111.0 for 1,4‐dichlorobenzene (internal standard). The standard curve was linear (r² ≥ 0.995) over the concentration ranges of 5–800 ng/mL. The lower limit of quantification was 5 ng/mL using 50 μL of rat plasma. The coefficient of variation and relative error for intra‐ and interassays at four quality control levels were 3.1–13.9% and ?4.0–2.6%, respectively. The stability of processing (freeze–thaw, long‐term storage at ?80°C, and short‐term storage at room temperature) and chromatography (reinjection) was shown to be of insignificant effect. The present method was applied successfully to the pharmacokinetic study of α‐cedrene after its intravenous (10 mg/kg) and oral (25 mg/kg) administration in male Sprague‐Dawley rats.     

Metal Enhanced Electrochemical Cyclooxygenase‐2 (COX‐2) Sensor for Biological Applications

Pain measurement is commonly required in biomedical and other emergency situations, yet there has been no pain biosensor reported in literature. Conventional approaches for pain measurement relies on Wong‐Baker face diagrams, which are grossly inadequate for situations involving children or unconscious people. We report a label‐free immunosensor for monitoring the pain biomarker cylooxygenase‐2 (COX‐2) in blood. The sensor is based on the concept of metal‐enhanced detection (MED). MED relies on the idea that the immobilization of underpotential deposition (upd) metallic films deposited either as a monolayer or electrostatically held onto a solid gold substrate could significantly amplify bimolecular recognition such as involving antigen‐antibody (Ab‐Ag) interactions. The surface bound Ab‐Ag complex insulates the electrode; causing a decrease in concentration‐dependent redox signals. A linear detection range of (3.64–3640.00)×10^?4 ng/mL was recorded with a detection limit of 0.25×10^?4 ng/mL, which was 4 orders of magnitude lower than that reported for ELISA for the same biomarker. The immunosensor exhibited selectivity of less than 6 % for potential interferents.     

Fabrication of an Electrochemical E. coli Biosensor in Biowells Using Bimetallic Nanoparticle‐Labelled Antibodies

An electrochemical biosensor was developed for the determination of Escherichia coli (E. coli) in water. For this purpose, silver‐gold core‐shell (Ag@Au) bioconjugates and anti‐E. coli modified PS‐microwells were designed in a sandwich‐type format in order to obtain higher sensitivity and selectivity. Ag@Au bimetallic nanoparticles were synthesized by co‐reduction method. The core‐shell formation was analyzed by using UV‐Vis spectroscopy and transmission electron microscopy. Biotin labeled anti‐E. coli antibodies were coupled with Ag@Au nanoparticles to form bioconjugates. The electrochemical immunosensor was prepared by immobilizing anti‐E. coli on polystyrene (PS)‐microwells via chemical bonding. These modified microwells were identified with X‐ray photoelectron spectroscopy and surface enhanced Raman spectroscopy. E. coli was sandwiched between Ag@Au bioconjugates and anti‐E. coli on PS‐microwells at different concentrations. The relationship between the E. coli concentration and stripping current of gold ions (Au³⁺) were investigated by square wave anodic stripping voltammetry at pencil graphite electrode. The proposed method can provide some advantages such as lower detection limit and shorter detection time. The electrochemical response for the immunosensor was linear with the concentration of the E. coli in the range of 10¹ and 10⁵ cfu/mL with a limit of detection 3 cfu/mL. The procedure maintains good sensitivity and repeatability and also offers utility in the fields of environmental monitoring and clinical diagnosis.     

Ultrasensitive Electrochemical Immunosensor for Detection of Tumor Necrosis Factor‐α Based on Functionalized MWCNT‐Gold Nanoparticle/Ionic Liquid Nanocomposite

A novel and highly sensitive electrochemical immunosensor was developed for the detection of protein biomarker tumor necrosis factor‐alpha (TNF‐α) based on immobilization of TNF‐α‐antibody (anti‐TNF‐α) onto robust nanocomposite containing gold nanoparticles (AuNP), multiwalled carbon nanotubes (MWCNTs) and ionic liquid (1‐buthyl‐3‐methylimidazolium bis (trifluoromethyl sulfonyl)imide). Functionalized MWCNT‐gold nanoparticle was produced by one‐step synthesis based on the direct redox reaction. The electrochemical properties of nanocomposite were characterized by electrochemical impedance spectroscopy and cyclic voltammetry. The anti‐TNF‐α was immobilized or entrapped in the nanocomposite and used in a sandwich type complex immunoassay with anti‐TNF‐α labeled with horseradish peroxidase as secondary antibody. Under optimum conditions, the immunosensor could detect TNF‐α in a linear range from 6.0 to 100 pg mL^?1 with a low detection limit of 2.0 pg mL^?1. The simple fabrication method, high sensitivity, good reproducibility, stability, as well as acceptable accuracy for TNF‐α detection in human serum samples are the main advantages of this immunosensor, which might have broad applications in protein diagnostics and bioassay.     

Dual‐Amplification of Antigen–Antibody Interactions via Backfilling Gold Nanoparticles on (3‐Mercaptopropyl) Trimethoxysilane Sol‐Gel Functionalized Interface

A new dual‐amplification strategy of electrochemical signaling from antigen–antibody interactions was proposed via backfilling gold nanoparticles on (3‐mercaptopropyl) trimethoxysilane sol‐gel (MPTS) functionalized interface. The MPTS was employed not only as a building block for the electrode surface modification but also as a matrix for ligand functionalization with first amplification. The second signal amplification strategy introduced in this study was based on the backfilling immobilization of nanogold particles to the immunosensor surface. Several coupling techniques, such as with nanogold but not MPTS or with MPTS but not nanogold, were investigated for the determination of carcinoembryonic antigen (CEA) as a model, and a very good result was obtained with nanogold and MPTS coupling immunosensor. With the noncompetitive format, the formation of the antigen–antibody complex by a simple one‐step immunoreaction between the immobilized anti‐CEA and CEA in sample solution introduced membrane potential change before and after the antigen–antibody interaction. Under optimal conditions, the proposed immunosensor exhibited a good electrochemical behavior to CEA in a dynamic concentration range of 4.4 to 85.7 ng/mL with a detection limit of 1.2 ng/mL (at 3 δ). Moreover, the precision, reproducibility and stability of the as‐prepared immunosensor were acceptable. Importantly, the proposed methodology would be valuable for diagnosis and monitoring of carcinoma and its metastasis.     

Gold Nanoparticle‐Based Redox Signal Enhancement for Sensitive Detection of Human Chorionic Gonadotropin Hormone

A sensitive immunosensor for the detection of pregnancy marker, human chorionic gonadotropin hormone (hCG), was developed using the direct electrical detection of Au nanoparticles. We utilized disposable screen‐printed carbon strips (SPCSs) for the development of our immunosensor, which provided cost‐effective tests with the required antigen sample volume as small as 2 μL. After the recognition reaction between the surface‐immobilized primary antibody and hCG, the captured antigen was sandwiched with a secondary antibody that was labeled with Au nanoparticles. Au nanoparticles were exposed to a preoxidation process at 1.2 V for 40 s, which was subsequently followed with a reduction scan on the same surface using differential pulse voltammetry (DPV). We could observe Au nanoparticle‐labeled antigen‐antibody complexes immobilized on the surface of SPCS using scanning electron microscopy (SEM). Additionally, the number of Au nanoparticles on the immunosensor was determined using SEM images, and showed a linear relationship with the current intensity obtained from the DPV measurements with a detection limit of 36 pg/mL hCG (612 fM, 3.6×10^?4 IU/mL). Our immunosensor system, a combination of the screen‐printing technology with Au nanoparticles provides a promising biosensor for various applications in life sciences.