Carcinoembryonic Antigen In Human Serum Samples Research Articles

Label free and ultrasensitive electrochemical detection of carcinoembryonic antigen using a disposable aptasensor based on Pd and graphene

We prepared an electrochemical aptasensor for label-free analysis of carcinoembryonic antigen (CEA). Herein, PdNPs were synthesized on the surface of graphene-modified screen-printed carbon electrodes (Pd-GN/SPCE) via electrochemical method for immobilisation of CEA aptamer as a bio-recognition element. The morphological characterizations of the fabricated Pd-GN/SPCE were performed using SEM, EDX, and elemental mapping that confirmed the successful electrochemical deposition of PdNPs. A disposable aptasensor for ultrasensitive electrochemical measurement of CEA was proposed by immobilising CEA aptamer on Pd-GN/SPCE. The electrochemical measurements were performed using 5 mM [Fe(CN)6]3-/4- as a redox probe. The electrochemical deposition of PdNPs improved the electrical conductivity resulting in enhanced current response for the redox probe. When CEA antigen interacts with CEA aptamer, it reduces the oxidation and reduction current of [Fe(CN)6]3-/4- due to the attachment of biomolecules to the electrode surfaces that hinders the electron transfer. The current changes of the redox species before and after CEA binding were measured using DPV. The developed aptasensor possessed a wide calibration range of 0.002–200 ng/mL and detection limit of 1.0 pg/mL. The aptamer-immobilised electrode provides an exceptional selectivity, reproducibility, and sensitive measurement of CEA. Moreover, the effective sensing of CEA in human serum samples with great recoveries (99.4––106 %) demonstrated its capability for clinical analysis.

Highly sensitive electrochemical immunosensor based on electrodeposited platinum nanostructures confined in silica nanochannels for the detection of the carcinoembryonic antigen.

In this study, we report a highly sensitive electrochemical immunosensor for carcinoembryonic antigen (CEA) detection based on the electrodeposited platinum nanoparticles (Pt NPs) confined in the ultrasmall nanochannels of vertically ordered mesoporous silica film (VMSF). VMSF bearing amine groups (NH2-VMSF) can be prepared on the indium tin oxide electrode surface via a one-step co-condensation route using an electrochemically assisted self-assembly method, which renders a strong electrostatic effect for [PtCl6]2- and leads to the spatial confinement of Pt NPs inside the silica nanochannels after electrodeposition. The external surface of NH2-VMSF is functionalized with CEA antibodies using glutaraldehyde as a coupling agent, resulting in an electrochemical immunosensing interface with good specificity for CEA detection. Under optimal experimental conditions, high affinity between the CEA antibody and CEA produces a steric hindrance effect for the accessibility of the electrochemical probe ([Fe(CN)6]3-) in the bulk solution to the underlying indium tin oxide surface, eventually resulting in the attenuated electrochemical signal and enabling the detection of the CEA with a wide linear range of 0.01pg/mL∼10ng/mL and a pretty low limit of detection of 0.30fg/mL. Owing to the signal amplification ability of Pt NPs and the anti-biofouling property of NH2-VMSF, the as-prepared electrochemical immunosensor based on the Pt NPs@NH2-VMSF displays an accurate analysis of the CEA in human serum samples, holding significant promise for health monitoring and clinical diagnosis.

Probe-integrated electrochemical immunosensor based on electrostatic nanocage array for reagentless and sensitive detection of tumor biomarker.

Sensitive detection of tumor biomarkers is crucial for early diagnosis and prognosis evaluation of cancer. Owing to no need of labelled antibody, formation of sandwich immunocomplexes and additional solution-based probe, probe-integrated electrochemical immunosensor for reagentless detection of tumor biomarkers is highly desirable. In this work, sensitive and reagentless detection of a tumor biomarker is realized based on fabrication of a probe-integrated immunosensor by confining redox probe in electrostatic nanocage array modified electrode. Indium tin oxide (ITO) electrode is employed as the supporting electrode because it is cheap and easily available. The silica nanochannel array consisted of two layers with opposite charges or different pore diameters was designated as bipolar films (bp-SNA). In this work, Electrostatic nanocage array is equipped on ITO electrode by growth of bp-SNA with two layered nanochannel array having different charge properties including a negatively charged silica nanochannel array (n-SNA) and a positively charged amino-modified SNA (p-SNA). Each SNA can be easily grown with 15s using electrochemical assisted self-assembly method (EASA). Methylene blue (MB) is applied as the model electrochemical probe with positive charge to be confined in electrostatic nanocage array with stirring. The combination of the electrostatic attraction from n-SNA and the electrostatic repulsion from p-SNA endows MB with highly stable electrochemical signal during continuous scanning. When the amino groups of p-SNA are modified using the bifunctional glutaraldehyde (GA) to introduce aldehydes, the recognitive antibody (Ab) of the most commonly used tumor biomarker, carcinoembryonic antigen (CEA), can be covalently immobilized. After the non-specific sites are blocked, the immunosensor is successfully fabricated. As the formation of antigen-antibody complex decreases electrochemical signal, the immunosensor can achieve reagentless detection of CEA ranged from 10pg/mL to 100ng/mL with a low limit of detection (LOD, 4pg/mL). Determination of CEA in human serum samples is realized with high accuracy.

A novel ratiometric electrochemical aptasensor for highly sensitive detection of carcinoembryonic antigen

A novel ratiometric electrochemical aptasensor was proposed for carcinoembryonic antigen (CEA) detection based on exonuclease III (Exo III)-assisted recycling and rolling circle amplification (RCA) strategies. A thiolated ferrocene-labeled hairpin probe 2 (Fc-HP2) was fixed on the gold nanoparticles (AuNPs)-modified gold electrode (AuE) surface through Au–S bonds. The presence of CEA led to the release of trigger, which hybridized with the 3′-protruding of hairpin probe 1 (HP1) and triggered the Exo III cleavage reaction, accompanied by the releasing of trigger and generation of new DNA fragment which was used for the successive hybridization with Fc-HP2. After the Exo III cleavage process, the remaining Fc-HP2 fragments hybridized as primers with the RCA template to initiate the RCA process, and long single-stranded polynucleotides were produced for methylene blue (MB) binding. Such changes resulted in the signal of Fc (IFc) decreased and that of MB (IMB) increased, achieving a linear relationship between IMB/IFc and logarithm of CEA concentrations ranging from 1.0 pg mL−1 to 100.0 ng mL−1 with a detection limit of 0.59 pg mL−1. Additionally, the developed aptasensor had been successfully applied to detect CEA in human serum samples. Therefore, the proposed strategy might provide a new platform for clinical detections of CEA.

Electrochemiluminescence biosensor for carcinoembryonic antigen detection based on Au-Ag/g-C3N4 nanocomposites

Herein, an electrochemiluminescence (ECL) aptasensor for carcinoembryonic antigen (CEA) detection was developed based on Au-Ag/g-C3N4 nanocomposites (NCs), which were synthesized by decorating graphitic carbon nitride (g-C3N4) nanosheets with alloy-structured Au-Ag bimetallic nanoparticles (NPs) via one-step in situ chemical reduction. As ECL sensing platform, Au-Ag/g-C3N4 NCs could significantly improve the ECL intensity of luminol due to the good conductivity of Au-Ag NPs, electrocatalytic activity for oxygen evolution reaction (OER) and the ability to adsorb luminol via π stacking interaction. In addition, it could load the thiol terminated aptamers of CEA via Au-S or Ag-S bonds. In the presence of CEA, the ECL response of the proposed biosensor decreased significantly due to the fact that the assembled protein layers hindered the electron transfer and the diffusion of ECL reactants toward the electrode surface. The proposed ECL sensor exhibited a good linear relationship with CEA in the range of 1.0–1.0 × 10−6 ng/mL with a detection limit of 8.9 × 10−7 ng/mL. The satisfactory results were obtained in the detection of CEA in human serum samples.

A reagentless electrochemical immunosensor for sensitive detection of carcinoembryonic antigen based on the interface with redox probe-modified electron transfer wires and effectively immobilized antibody

Convenient and sensitive detection of tumors marked in serum samples is of great significance for the early diagnosis of cancers. Facile fabrication of reagentless electrochemical immunosensor with efficient sensing interface and high sensitivity is still a challenge. Herein, an electrochemical immunosensor was easily fabricated based on the easy fabrication of immunoassay interface with electron transfer wires, confined redox probes, and conveniently immobilized antibodies, which can achieve sensitive and reagentless determination of the tumor marker, carcinoembryonic antigen (CEA). Carboxyl multi-walled carbon nanotubes (MWCNTs) were firstly modified with an electrochemical redox probe, methylene blue (MB), which has redox potentials distinguished from those of redox molecules commonly existing in biological samples (for example, ascorbic acid and uric acid). After the as-prepared MB-modified MWCNT (MWCNT-MB) was coated on the supporting glassy carbon electrode (GCE), the MWCNT-MB/GCE exhibited improved active area and electron transfer property. Polydopamine (PDA) was then in situ synthesized through simple self-polymerization of dopamine, which acts as the bio-linker to covalently immobilize the anti-CEA antibody (Ab). The developed immunosensor could be applied for electrochemical detection of CEA based on the decrease in the redox signal of MB after specific binding of CEA and immobilized Ab. The fabricated immunosensor can achieve sensitive determination of CEA ranging from 10 pg/ml to 100 ng/ml with a limit of detection (LOD) of 0.6 pg/ml. Determination of CEA in human serum samples was also realized with high accuracy.

Engineering a G-quadruplex-based logic gate platform for sensitive assay of dual biomarkers of ovarian cancer

As most single tumor markers have low sensitivity or specificity, the joint detection of multiple tumor biomarkers is helpful to improve the positive rate and specificity of early diagnosis. To establish a sensitive, specific, and rapid screening method for ovarian cancer, two enzyme-free logic gates were developed to realize the joint detection of carbohydrate antigen 125 (CA125) and carcinoembryonic antigen (CEA). G-quadruplex with peroxidase activity was used as a chromogenic catalyst in this colorimetric diagnosis. For NOR gate, in the absence of CEA and CA125, template DNA (Tem-DNA), CEA aptamer with half of the G-quadruplex sequence (CEA-apt), and CA125 aptamer with the other half of the G-quadruplex sequence (CA125-apt) form a double-stranded DNA equipped with one G-quadruplex structure which can strongly combine with hemin to obtain the peroxidase-like activity; here, the output of this NOR gate is set as 1, which could exclude the risk of ovarian cancer. For AND gate, CEA-apt and CA125-apt are separated from magnetic beads in the co-existence of the dual biomarkers. After adding Tem-DNA, the G-quadruplex structure constructs with hemin to exhibit the output as 1, presenting a high risk of ovarian cancer. Under the optimized condition, this novel assay can not only show a sharp color difference between physiological state and pathological state, but also be employed for the quantitative analysis of every single biomarker. The linear detection range and detection limit for CEA are 5–500 ng mL−1 and 0.88 ng mL−1, while they are for CA125 are 35–500 U mL−1 and 0.91 U mL−1, respectively. Moreover, the established approach was successfully applied in detecting CA125 and CEA in human serum samples, which provides great promise in the fields of clinical examination and disease diagnosis.

A label-free ECL aptasensor for sensitive detection of carcinoembryonic antigen based on CdS QDs@MOF and TEOA@Au as bi-coreactants of Ru(bpy)32+

Herein, a label-free electrochemiluminescence (ECL) biosensor for sensitive determination of carcinoembryonic antigen (CEA) was fabricated based on CdS quantum dots loaded onto metal organic framework (CdS QDs@MOF) and triethanolamine modified on gold nanoparticles (TEOA@AuNPs) as bi-coreactants of Ru(bpy)32+ ECL system. The TEOA@AuNPs served as not only coreactant of Ru(bpy)32+ but also nanocarrier for CEA aptamer which was bonded to the TEOA@AuNPs through Au–S bond. After incubated in CEA solution, the ECL signals decreased due to the poor conductivity of CEA and there was a linear correlation between the ECL intensity and log(CCEA). Based on this result, a label-free ECL biosensor has been developed successfully and used to detect CEA with a detection limit of 8.5 × 10−5 ng/mL. The proposed ECL aptasensor had good analytical performance in the detection of CEA in human serum samples.

Biocatalyst and colorimetric biosensor of carcinoembryonic antigen constructed via chicken egg white-copper phosphate organic/inorganic hybrid nanoflowers

In this article, the dual-functional chicken egg white-copper phosphate organic-inorganic hybrid nanoflowers (Cu-NFs), combining the functions of signal amplification and biological recognition, were prepared through a simple one-pot method. The Cu-NFs exhibit excellent biocatalytic activity of peroxidase and polyphenol oxidase. Besides, a biotin-labeled secondary antibody encapsulated Cu-NFs-2 (Cu-NFs-2@Biotin-NHS-Ab2) capture probe was prepared by using the interaction between avidin in the egg white and biotin. Based upon this superiority, the as-prepared Cu-NFs-2 were used in labeled avidin-biotin enzyme-linked immunosorbent assay (Cu-NFs-2 based-LAB-ELISA) to construct a sensitive colorimetric biosensor for the ultrasensitive detection of carcinoembryonic antigen (CEA). Under weak alkaline (pH = 7.5) conditions, the as-developed colorimetric sensor displayed a wide linear range of 0.05–40 ng/mL with a detection limit of 3.52 pg/mL. Furthermore, this colorimetric sensor has been successfully applied to the detection of CEA in human serum samples. Therefore, the as-developed colorimetric sensor has broad application prospects in the field of medical diagnosis and portable detection.

An Electrochemical Aptasensor for Highly Sensitive Detection of CEA Based on Exo III and HCR Dual Signal Amplification

At present, Carcinoembryonic antigen（CEA）is considered as a broad-spectrum tumor biomarker, the accurate analysis of CEA in clinical samples can assist early diagnosis and treatment of cancer. Herein，a novel electrochemical aptasensor has been proposed for CEA detection based on Exo III and HCR dual signal amplification. The target CEA specifically is binded to aptamer region in H1 through a strong attraction, thereby triggering the CHA cycle to form plenty of H1@H2 duplex. Subsequently, the Exonuclease III digested complex and liberated the target to induce the first signal amplification, and generated a large number of trigger chains simultaneously. Then, these triggers can hybridize with the capture probes and MB-labeled S1 and S2, producing amplified electrochemical signal significantly on the electrode surface. The integration of HCR and EXO-III assisted target circulation endowed the sensor excellent analytical performance for the detection of CEA, with a wide linear range from 10 pg.ml -1 to 100 ng.ml -1 , high sensitivity of limit of detection (LOD) of 1.2 pg.ml -1 . What’s more, the biosensing strategy was successfully verified for directly identifying CEA in human serum samples and exhibited admirable stability and precision. Therefore, this elaborated sensor opens a new simple way for detecting CEA and exhibits a great promise in the early screening of tumor.

Ultrasensitive detection of protein biomarkers by MALDI-TOF mass spectrometry based on ZnFe2O4 nanoparticles and mass tagging signal amplification

A facile MALDI-TOF mass spectrometric platform for quantitative analysis of protein biomarkers was developed based on magnetic ZnFe2O4 nanoparticles and mass tagging signal amplification. In this platform, magnetic ZnFe2O4 nanoparticles functionalized with an aptamer of the biomarker of interest was used to magnetically separate silica nanoparticles modified with another aptamer of the target biomarker and a barcoding peptide from solution phase in the presence of the biomarker of interest. After the silica nanoparticles were dissolved by KHF2, the released barcoding peptide was detected by MALDI-TOF mass spectrometry with magnetic ZnFe2O4 nanoparticles used as assisting matrix of laser desorption ionization. Since the mass spectral intensity of the barcoding peptide is directly related to the concentration of the target biomarker, the proposed platform can be applied to the quantification of the target biomarker in complex biological samples. The effectiveness of the proposed platform was tested on the detection of carcinoembryonic antigen (CEA) in serum. Experimental results revealed that the proposed platform could achieve quite reliable quantitative results for CEA in human serum samples with accuracy comparable to a commercial CEA ELISA Kit. Its limit of detection and limit of quantification for CEA were estimated to be 0.6 × 10−3 and 1.8 × 10−3 ng/mL, respectively, considerably lower than the corresponding values reported in literature. Due to its features of simplicity in design, extremely low background signal, high sensitivity and selectivity, the proposed method can be further developed to be a competitive alternative for the quantification of CEA and other protein biomarkers as well.

CdS Quantum-Dots-Decorated V2O5 Nanosheets as Chemically Etchable Active Materials for Sensitive Photoelectrochemical Immunoassay of Carcinoembryonic Antigen.

We report here CdS quantum-dots (QDs)-decorated V2O5 nanosheets as high-performance and chemically etchable photoelectric active materials for constructing a photoelectrochemical (PEC) immunoassay platform. CdS QDs-decorated V2O5 nanosheets as new photoelectric materials can show superior photocurrent to V2O5 nanosheets and CdS QDs under visible-light irradiation because of the promoted photogenerated electron-hole separation and the increased visible-light absorption. V2O5 nanosheets can be etched by ascorbic acid (AA) because of the reduction of V2O5 to V4+, and the photocurrent of CdS/V2O5-nanocomposite-modified indium tin oxide electrode decreases significantly after being etched by AA. Inspired by this phenomenon, a PEC immunoassay platform is constructed for carcinoembryonic antigen (CEA) detection by using CdS/V2O5 nanocomposite as the photoelectric material and AA-encapsulated liposome immunonanocapsules as labels. The linear detection range for detecting CEA is from 0.5 pg mL-1 to 1 ng mL-1, with a limit of detection of 0.1 pg mL-1. The proposed method also shows good selectivity, excellent reproducibility, and satisfactory recovery in detection of CEA in human serum samples. We believe that this work will lay the foundation for the future development of V2O5-based materials for PEC analysis, and also provide a reasonable design and implementation for the development of PEC immunoassay.

A sandwich-type photoelectrochemical immunosensor based on ReS2 nanosheets for high-performance determination of carcinoembryonic antigen

Photoelectrochemical (PEC) sensing system has received much more attention as a powerful strategy for detecting trace substances. Herein, a sandwich-type PEC immunosensor constructed by two-dimension rhenium disulfite nanosheets (2D-ReS2) was developed for high-performance detection of carcinoembryonic antigen (CEA). 2D-ReS2 was facilely exfoliated from bulk crystals by ultrasonication in a mixture of 1,3-di-(3-mercaptopropyl)-imidazolium bromide (DMimBr) ionic liquid and alcohol. Then, ReS2 nanosheets were modified onto a glassy carbon electrode surface to construct an interface for fabricating a sandwich-type PEC immunosensing platform which has been accomplished by successive immobilizing anti-CEA antibody (Ab1), binding CEA and capturing the alkaline phosphatase labeled CEA antibody (ALP-Ab2). The introduced alkaline phosphatase can efficiently catalyze vitamin C magnesium phosphate to afford ascorbic acid (AA). Ascorbic acid can serve as an electron donor to capture holes photogenerated from ReS2 nanosheets to produce photocurrent signal for CEA detection. The PEC immunosensor shows superior stability, selectivity, sensitivity, and accuracy for CEA determination. An extremely low detection limit of 0.468 pg mL−1 with a broad linear range of 0.0005 ∼ 10.0 ng mL−1 can be obtained for CEA determination. The PEC immunosensor can be applied for determining CEA in human serum samples with good selectivity and accuracy, demonstrating promising potential in biomedical analysis.

Development of an Immunosensor Based on the Exothermic Reaction between H2O and CaO Using a Common Thermometer as Readout.

Thermometers, one of the most commonly used instruments at home, are normally adapted to measure temperature directly with high accuracy but rarely adopted to act as readout in the biosensors. It is necessary to find some ways to establish a relationship between the concentration of the target and the temperature change. In this study, a common thermometer was used as readout to develop a convenient immunosensor. The designed immunosensor comprises three components, including target recognition area, water flow system, and exothermic reaction bottle. The capture antibody for the target [carcinoembryonic antigen (CEA) was selected as a model target] was preloaded on the bottom of the recognition area. In the presence of CEA, a sandwich-type structure was formed between the capture antibody, CEA, and biotinylated detection antibody. Then, the streptavidin-functionalized platinum nanoparticles were labeled on the detection antibody due to biotin-avidin interaction. The captured platinum nanoparticles can effectively catalyze the decomposition of H2O2 into O2. The continuous production of gas resulted in pressure increment inside the reaction bottle and further pushed the water flow into the exothermic reaction bottle. Finally, the water reacted with calcium oxide to generate a large amount of heat in the exothermic reaction bottle; thereby the temperature inside the bottle was enhanced and recorded by a common thermometer easily. The temperature enhancement has a linear relationship with the CEA concentration in the range of 7.81-500 pg/mL with a detection limit of 0.6 pg/mL. Furthermore, by taking advantage of simplicity, compatibility, stability, and high sensitivity, our temperature-based immunoassay has been applied to detect CEA in human serum samples with satisfactory results.

Graphene Quantum Dots Decorated Gold-Polyaniline Nanowire for Impedimetric Detection of Carcinoembryonic Antigen

A label-free impedimetric immunosensor based on N, S-graphene quantum dots@Au-polyaniline (N, S-GQDs@Au-PANI) nanowires was fabricated for the quantitative detection of carcinoembryonic antigen (CEA). The N, S-GQDs and Au-PANI were synthesized by a simple hydrothermal pyrolysis and interfacial polymerization, respectively. Subsequently, 2–9 nm N, S-GQDs are successfully decorated onto 30–50 nm Au-PANI nanowires by Au-thiol linkage to serve as the bifunctional probe for amplifying the electrochemical activity as well as anchoring anti-CEA. The N, S-GQDs@Au-PANI nanowires are excellent conducting materials to accelerate the electron transfer, while the formation of CEA antibody-antigen bioconjugates after the addition of CEA significantly increase the charge transfer resistance, and subsequently provides a highly stable and label-free immunoassay platform for the impedimetric detection of CEA. The label-free immunosensor exhibits a wide linear range from 0.5 to 1000 ng mL−1 with a low detection limit of 0.01 ng mL−1. The N, S-GQDs@Au-PANI based immunosensor also shows high selectivity and stability over other cancer makers and amino acids. Moreover, this promising platform is successfully applied to the detection of CEA in human serum samples with excellent recovery of (96.0 ± 2.6)–(103 ± 3.8)%. These results clearly demonstrate a newly developed highly efficient and label-free impedimetric immunosensor for the detection of CEA using N, S-GQDs@Au-PANI nanowires as the biosensing probe, which can pave the gateway for the fabrication of high performance and robust impedimetric immunosensor to detect cancer makers in early stage of cancer diagnosis and therapy.

A novel nitrogen and sulfur co-doped carbon dots-H2O2 chemiluminescence system for carcinoembryonic antigen detection using functional HRP-Au@Ag for signal amplification.

A novel nitrogen and sulfur co-doped carbon dots (NS-CDs)-H2O2 chemiluminescence (CL) system was developed to detect carcinoembryonic antigen (CEA) by taking advantage of dual-signal amplification of functional Au@Ag nanoparticles (NPs) nanoprobes. Horseradish peroxidase (HRP) and the complementary DNA were co-immobilized onto Au@Ag NPs surface to shape the functional nanoprobes (HRP-Au@Ag-cDNA) for signal amplification. In this proposal, HRP-Au@Ag-cDNA was specifically hybridized with CEA aptamer-functionalized magnetic beads to form the double-strand hybridization nanocomposites (HRP-Au@Ag-dsDNA-MB). Upon the addition of CEA, the CEA aptamer preferred to bind with CEA instead of double-strand hybridization interaction, thus HRP-Au@Ag-dsDNA-MB was dehybridized and the HRP-Au@Ag-cDNA nanoprobe was released. The synergistic catalytic effects of HRP and Au @Ag NPs endow the nanoprobe producing a dual CL signal amplification in the NS-CDs-H2O2 CL system. The CL intensity of the developed strategy enhanced with CEA concentration increasing in the range of 0.3-80 ng mL-1. Benefiting from the synergistic effect, a detection limit as low as 94 pg mL-1 was obtained. Moreover, successful application of this CL sensing platform was achieved for the determination of CEA in human serum samples, demonstrating the promising prospect in the early tumor warning and therapeutic monitoring.

Three dimensional sea-urchin-like PdAuCu nanocrystals/ferrocene-grafted-polylysine as an efficient probe to amplify the electrochemical signals for ultrasensitive immunoassay of carcinoembryonic antigen

A novel sandwich-like immunosensor was efficiently fabricated for detection of carcinoembryonic antigen (CEA) with three dimensional sea-urchin-like PdAuCu nanocrystals (PdAuCu NCs)/ferrocene-grafted-polylysine (Fc-g-PLL) as the label of secondary antibodies (Ab2) and Au nanoparticles (Au NPs) as the substrate material. Herein, PdAuCu NCs were directly synthesized with polyethylene oxide (PEO) as a growth-directing agent by a facile one-step aqueous method without any organic solvent. Meanwhile, Fc-g-PLL was obtained by covalent linkage of Fc with PLL via Schiff-base reaction. The well-dispersed PdAuCu NCs by Fc-g-PLL have the enlarged surface area, enhanced catalytic properties and superior biocompatibility to amplify the current signals. The resultant immunosensor shows linear relationship of the electrochemical responses with the CEA concentrations within a broader linear range (0.001–100.0 ng mL–1) and a lower detection limit (0.23 pg mL–1, S/N = 3). Furthermore, the immunosensor was explored for practical assay of CEA in human serum samples with accredited results. The novel immunoassay provides a feasible platform for early medical diagnosis.

Electrochemical detection of carcinoembryonic antigen

In this work, a sandwich-type electrochemical immunosensor for carcinoembryonic antigen (CEA) detection has been constructed and tested. Unlike many other sensors using external electrochemical species in the electrolyte to generate an electrochemical signal, a ferrocene derivative has been integrated into the design of the sensor to provide an internal reporting system, allowing detection of CEA in buffers and biological samples. Gold nanoparticles, which have been used to increase the conductivity of sensing surfaces, also carry immobilized secondary anti-CEA and a ferrocene derivative. The shelf life testing of the sensor shows good performance after storage for 4 weeks. The sensor has been calibrated against different concentration of the target protein using square wave voltammetry. The calibration curve has been obtained in the range of 0.05–20ngmL−1, and the detection limit for CEA is ~ 0.01ngmL−1. The capability of the immunosensor has been verified by performing detection of CEA in human serum samples.

Sensitive immunosensing of the carcinoembryonic antigen utilizing aptamer-based in-situ formation of a redox-active heteropolyacid and rolling circle amplification

A highly sensitive electrochemical scheme for the detection of the cancer biomarker carcinoembryonic antigen (CEA) is reported. An aptamer-based formation of redox-active molybdophosphate is combined with rolling circle amplification (RCA). Gold nanoparticles (AuNPs) were utilized as supporting matrix for the aptamer and the primer to increase the primer/aptamer loading. The formation of a sandwich structure of anti-CEA/CEA/AuNP − aptamer-primer onto a glassy carbon electrode surface enabled an effective RCA reaction. Square wave voltammetry was applied to record the current signal at a peak potential of 0.18 V vs. Ag/AgCl. Compared to the immunosensor without RCA, the sensitivity of the immunosensor with RCA is increased by about a factor of 6. In the latter case, a wider linear range was obtained for the determination of CEA (from 0.5 pg mL−1 to 1 ng mL−1) with a detection limit as low as 0.1 pg mL−1. The practical applicability of the method was studied by analyzing CEA in human serum samples. The results were found to be in good agreement with those obtained by a reference method. Conceivably, the method can be applied to other DNA amplifications and therefore has the potential of finding wide applications.

Electrochemiluminescence immunoassay for the carcinoembryonic antigen using CdSe:Eu nanocrystals

CdSe:Eu nanocrystals were successfully synthesized and characterized by transmission electron microscopy, X-ray powder diffraction, and X-ray photoelectric spectroscopy. The CdSe:Eu nanocrystals showed enhanced green electrochemiluminescence (ECL) intensity when compared to pure CdSe nanocrystals. Further, the nanocrystals were used to design an ECL immunosensor for the detection of carcinoembryonic antigen (CEA) that has a linear response over the 1.0 fg·mL−1 to 100 ng·mL−1 CEA concentration range with a 0.4 fg·mL−1 detection limit. The assay was applied to the determination of CEA in human serum samples.