Carbon nanotube-based symbiotic coaxial nanocables with nanosilica and nanogold particles as labels for electrochemical immunoassay of carcinoembryonic antigen in biological fluids

A feasible and practicable amperometric immunoassay strategy for sensitive screening of carcinoembryonic antigen (CEA) in human serum was developed using carbon nanotube (CNT)-based symbiotic coaxial nanocables as labels. To construct such a nanocable, a thin layer of silica nanoparticles was coated on the CNT surface by sonication and sol-gel methods, and then colloidal gold nanoparticles were assembled on the amino-functionalized SiO₂/CNTs, which were used for the label of horseradish peroxidase-anti-CEA conjugates (HRP-anti-CEA-Au/SiO₂/CNT). In the presence of analyte CEA, the sandwich-type immunocomplex was formed on an anti-CEA/Au/thionine/Nafion-modified glassy carbon electrode by using HRP-anti-CEA-Au/SiO₂/CNTs as detection antibodies. To embody the advantages of the protocol, the analytical properties of variously modified electrodes were compared in detail on the basis of different nanolabels. Under optimal conditions, the cathodic peak currents of the electrochemical immunosensor were proportional to the logarithm of CEA concentration over the range from 0.01 to 12 ng mL⁻¹ in pH 5.5 HAc-NaAc containing 5 mM H₂O₂. At a signal-to-noise ratio of 3, the detection limit (LOD) is 5 pg mL⁻¹ CEA. Intra- and inter-assay coefficients of variation were below 9.5%. Meanwhile, the selectivity and stability of the immunosensor were acceptable. In addition, the technique was evaluated by spiking CEA standards in pH 7.4 PBS and with 35 clinical serum specimens, receiving excellent accordance with results from commercially available electrochemiluminescent enzyme-linked immunoassay.     

Ultrasensitive electrochemical immunoassay for carcinoembryonic antigen based on three-dimensional macroporous gold nanoparticles/graphene composite platform and multienzyme functionalized nanoporous silver label

Three-dimensional macroporous gold nanoparticles/graphene composites (3D-AuNPs/GN) were synthesized through a simple two-step process, and were used to modify working electrode sensing platform, based on which a facile electrochemical immunoassay for sensitive detection of carcinoembryonic antigen (CEA) in human serum was developed. In the proposed 3D-AuNPs/GN, AuNPs were distributed not just on the surface, but also on the inside of graphene. And this distribution property increased the area of sensing surface, resulting in capturing more primary antibodies as well as improving the electronic transmission rate. In the presence of CEA, a sandwich-type immune composite was formed on the sensing platform, and the horseradish peroxidase-labeled anti-CEA antibody (HRP-Ab₂)/thionine/nanoporous silver (HRP-Ab₂/TH/NPS) signal label was captured. Under optimal conditions, the electrochemical immunosensor exhibited excellent analytical performance: the detection range of CEA is from 0.001 to 10 ng mL⁻¹ with low detection limit of 0.35 pg mL⁻¹ and low limit of quantitation (LOQ) of 0.85 pg mL⁻¹. The electrochemical immunosensor showed good precision, acceptable stability and reproducibility, and could be used for the detection of CEA in real samples. The proposed method provides a promising platform of clinical immunoassay for other biomolecules     

Ultrasensitive electrochemical immunosensors for multiplexed determination using mesoporous platinum nanoparticles as nonenzymatic labels

An ultrasensitive multiplexed immunoassay method was developed at a disposable immunosensor array using mesoporous platinum nanoparticles (M-Pt NPs) as nonenzymatic labels. M-Pt NPs were prepared by ultrasonic method and employed to label the secondary antibody (Ab₂) for signal amplification. The immunosensor array was constructed by covalently immobilizing capture antibody (Ab₁) on graphene modified screen printed carbon electrodes (SPECs). After the sandwich-type immunoreactions, the M-Pt-Ab₂ was bound to immunosensor surface to catalyze the electro-reduction of H₂O₂ reaction, which produced detectable signals for readout of analytes. Using breast cancer related panel of tumor markers (CA125, CA153 and CEA) as model analytes, this method showed wide linear ranges of over 4 orders of magnitude with the detection limits of 0.002 U mL⁻¹, 0.001 U mL⁻¹ and 7.0 pg mL⁻¹ for CA125, CA153 and CEA, respectively. The disposable immunosensor array possessed excellent clinical value in cancer screening as well as convenient point of care diagnostics.     

Nanogold–polyaniline–nanogold microspheres-functionalized molecular tags for sensitive electrochemical immunoassay of thyroid-stimulating hormone

Methods based on nanomaterial labels have been developed for electrochemical immunosensors and immunoassays, but most involved low sensitivity. Herein a novel class of molecular tags, nanogold–polyaniline–nanogold microspheres (GPGs), was first synthesized and functionalized with horseradish peroxidase-conjugated thyroid-stimulating hormone antibody (HRP-Ab₂) for sensitive electrochemical immunoassay of thyroid-stimulating hormone (TSH). X-ray diffraction, confocal Raman spectroscopy, scanning electron microscope and transmission electron microscope were employed to characterize the prepared GPGs. Based on a sandwich-type immunoassay format, the assay was performed in pH 5.0 acetate buffer containing 6.0 mmol L⁻¹ H₂O₂ by using GPG-labeled HRP-Ab₂ as molecular tags. Compared with pure polyaniline nanospheres and gold nanoparticles alone, the GPG hybrid nanostructures increased the surface area of the nanomaterials, and enhanced the immobilized amount of HRP-Ab₂. Several labeling protocols comprising HRP-Ab₂, nanogold particle-labeled HRP-Ab₂, and polyaniline nanospheres-labeled HRP-Ab₂, were also investigated for determination of TSH and improved analytical features were obtained by using the GPG-labeled HRP-Ab₂. With the GPG labeling method, the effects of incubation time and pH of acetate buffer on the current responses of the immunosensors were also studied. The strong attachment of HRP-Ab₂ to the GPGs resulted in a good repeatability and intermediate precision down to 7%. The dynamic concentration range spanned from 0.01 to 20 μIU mL⁻¹ with a detection limit (LOD) of 0.005 μIU mL⁻¹ TSH at the 3s_B criterion. Significantly, no significant differences at the 0.05 significance level were encountered in the analysis of 15 spiking serum samples between the developed electrochemical immunoassay and the commercially available enzyme-linked immunosorbent assay (ELISA) method for determination of TSH.     

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.     

Simultaneous electrochemical immunosensor based on water-soluble polythiophene derivative and functionalized magnetic material

A novel, sensitive electrochemical immunosensor for simultaneous determination of squamous cell carcinoma associated antigen (SCC-Ag) and carcinoembryonic antigen (CEA) for the combined diagnosis of cervical cancer was designed. The amplification strategy for electrochemical immunoassay was based on poly[3-(1,1′-dimethyl-4-piperidine-methylene) thiophene-2,5-diylchloride] (PDPMT-Cl) and functionalized mesoporous ferroferric oxide nanoparticles (Fe₃O₄ NPs). PDPMT-Cl dispersed in chitosan solution with enhanced electrical conductivity and solubility was used as matrices to immobilize the first antibodies. Different redox probes (thionine (Th) and ferrocenecarboxylic acid (Fca)) functionalized Fe₃O₄ NPs incubated with two kinds of secondary antibodies to fabricate the labels. Using an electrochemical analysis technique, two well-separated peaks were generated by Th and Fca, making the simultaneous detection of two analytes on the electrode possible. Under optimized conditions, this method showed wide linear ranges of three orders of magnitude with the detection limits of 4 pg mL⁻¹ and 5 pg mL⁻¹, respectively. The disposable immunosensor possessed excellent clinical value in cervical cancer screening as well as convenient point-of-care diagnostics.     

Nanogold-functionalized magnetic beads with redox activity for sensitive electrochemical immunoassay of thyroid-stimulating hormone

A new electrochemical immunosensor for sensitive determination of thyroid-stimulating hormone (TSH) was designed by using redox-active nanogold-functionalized magnetic beads (GoldMag) as signal tags on the nanogold–graphene interface. To construct such GoldMag nanostructures, polyethyleneimine-functionalized magnetic beads (PEI-MBs) were initially prepared by using a wet chemical method, and the electroactive thionine molecules and gold nanoparticles were then alternately immobilized on the surface of PEI-MBs by using an opposite-charged adsorption technique and an in situ synthesis method, respectively. The synthesized GoldMag nanostructures were utilized as signal tags for the label of horseradish peroxidase-anti-TSH conjugates (HRP-anti-TSH). With a sandwich-type immunoassay format, the conjugated signal tags on the transducer were increased with the increasing TSH concentration in the sample, thus enhancing the signal of the electrochemical immunosensor due to the labeled HRP toward the catalytic reduction of H₂O₂. Under optimal conditions, the current was proportional to the logarithm of TSH concentration ranging from 0.01 to 20 μIU mL⁻¹ in pH 6.0 HAc–NaAc containing 6 mM H₂O₂. The detection limit (LOD) was 0.005 μIU mL⁻¹ TSH at 3s_B. The immunosensor displayed an acceptable reproducibility, stability and selectivity. In addition, the methodology was evaluated with human serum specimens, receiving good correlation with results from commercially available electrochemiluminescent analyzer.     

An ultrasensitive luminol cathodic electrochemiluminescence immunosensor based on glucose oxidase and nanocomposites: Graphene–carbon nanotubes and gold-platinum alloy

In the present study, a novel and ultrasensitive electrochemiluminescence (ECL) immunosensor based on luminol cathodic ECL was fabricated by using Au nanoparticles and Pt nanoparticles (nano-AuPt) electrodeposited on graphene–carbon nanotubes nanocomposite as platform for the detection of carcinoembryonic antigen (CEA). For this introduced immunosensor, graphene (GR) and single wall carbon nanotubes (CNTs) dispersed in chitosan (Chi-GR-CNTs) were firstly decorated on the bare gold electrode (GE) surface. Then nano-AuPt were electrodeposited (DpAu-Pt) on the Chi-GR-CNTs modified electrode. Subsequently, glucose oxidase (GOD) was employed to block the non-specific sites of electrode surface. When glucose was present in the working buffer solution, GOD immediately catalyzed the oxidation of glucose to in situ generate hydrogen peroxide (H₂O₂), which could subsequently promote the oxidation of luminol with an amplified cathodic ECL signal. The proposed immunosensor was performed at low potential (−0.1 to 0.4 V) and low concentration of luminol. The CEA was determined in the range of 0.1 pg mL⁻¹ to 40 ng mL⁻¹ with a limit of detection down to 0.03 pg mL⁻¹ (S N⁻¹ = 3). Moreover, with excellent sensitivity, selectivity, stability and simplicity, the as-proposed luminol-based ECL immunosensor provided great potential in clinical 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.     

Enzyme-catalyzed silver deposition on irregular-shaped gold nanoparticles for electrochemical immunoassay of alpha-fetoprotein

A new and disposable electrochemical immunosensor was designed for detection of alpha-fetoprotein (AFP), as a model analyte, with sensitivity enhancement based on enzyme-catalyzed silver deposition onto irregular-shaped gold nanoparticles (ISGNPs). The assay was carried out with a sandwich-type immunoassay protocol by using ISGNP-labeled anti-AFP antibodies conjugated with alkaline phosphatase (ALP–Ab₂) as detection antibodies. The enzymatically catalytic deposition of silver on the electrode could be measured by stripping analysis in KCl solution due to the Ag/AgCl solid-state voltammetric process. Several labeling protocols including spherical gold nanoparticle-labeled ALP–Ab₂ and ISGNP-labeled ALP–Ab₂ were investigated for determination of AFP, and improved analytical properties were achieved with the ISGNP labeling. With the ISGNP labeling method, the effects of incubation time and incubation temperature for antigen-antibody reaction, and deposition time of silver on the current responses of the electrochemical immunosensors were also monitored. Under optimal conditions, the electrochemical immunosensor exhibited a wide dynamic range from 0.01 ng mL⁻¹ to 200 ng mL⁻¹ with a detection limit of 5.0 pg mL⁻¹ AFP. The immunosensor displayed a good stability and acceptable reproducibility and accuracy. No significant differences at the 95% confidence level were encountered in the analysis of 10 clinical serum samples between the developed immunoassay and the commercially available electrochemiluminescent method for determination of AFP.     

Platinum nanoparticles functionalized nitrogen doped graphene platform for sensitive electrochemical glucose biosensing

In this work, we reported an efficient platinum nanoparticles functionalized nitrogen doped graphene (PtNPs@NG) nanocomposite for devising novel electrochemical glucose biosensor for the first time. The fabricated PtNPs@NG and biosensor were characterized using transmission electron microscopy, high-resolution transmission electron microscopy, X-ray photoelectron spectroscopy, static water contact angle, UV–vis spectroscopy, electrochemical impedance spectra and cyclic voltammetry, respectively. PtNPs@NG showed large surface area and excellent biocompatibility, and enhanced the direct electron transfer between enzyme molecules and electrode surface. The glucose oxidase (GOx) immobilized on PtNPs@NG nanocomposite retained its bioactivity, and exhibited a surface controlled, quasi-reversible and fast electron transfer process. The constructed glucose biosensor showed wide linear range from 0.005 to 1.1 mM with high sensitivity of 20.31 mA M⁻¹ cm⁻². The detection limit was calculated to be 0.002 mM at signal-to-noise of 3, which showed 20-fold decrease in comparison with single NG-based electrochemical biosensor for glucose. The proposed glucose biosensor also demonstrated excellent selectivity, good reproducibility, acceptable stability, and could be successfully applied in the detection of glucose in serum samples at the applied potential of −0.33 V. This research provided a promising biosensing platform for the development of excellent electrochemical biosensors.     

Electrochemical immunosensor based on nanoporpus gold loading thionine for carcinoembryonic antigen

Nanoporous gold (NPG) has recently received considerable attention in analytical electrochemistry because of its good conductivity and large specific surface area. A facile layer-by-layer assembly technique fabricated NPG was used to construct an electrochemical immunosensor for carcinoembryonic antigen (CEA). NPG was fabricated on glassy carbon (GC) electrode by alternatively assembling gold nanoparticles (AuNPs) and silver nanoparticles (AgNPs) using 1,4-benzenedimethanethiol as a cross-linker, and then AgNPs were dissolved with HNO₃. The thionine was absorbed into the NPG and then gold nanostructure was electrodeposited on the surface through the electrochemical reduction of gold chloride tetrahydrate (HAuCl₄). The anti-CEA was directly adsorbed on gold nanostructure fixed on the GC electrode. The linear range of the immunosensor was from 10 pg mL⁻¹ to 100 ng mL⁻¹ with a detection limit of 3 pg mL⁻¹ (S/N = 3). The proposed immunosensor has high sensitivity, wide linear range, low detection limit, and good selectivity. The present method could be widely applied to construct other immunosensors.     

Fluorescence ELISA for sensitive detection of ochratoxin A based on glucose oxidase-mediated fluorescence quenching of CdTe QDs

The present study described a novel fluorescence enzyme-linked immunosorbent assay (ELISA) used to detect ochratoxin A (OTA) by using the glucose oxidase (GOx)-mediated fluorescence quenching of mercaptopropionic acid-capped CdTe quantum dots (MPA-QDs), in which GOx was used as an alternative to horseradish peroxidase (HRP) for the oxidization of glucose into hydrogen peroxide (H₂O₂) and gluconic acid. The MPA-QDs were used as a fluorescent signal output, whose fluorescence variation was extremely sensitive to the presence of H₂O₂ or hydrogen ions in the solution. Under the optimized conditions, the proposed fluorescence ELISA demonstrated a good linear detection of OTA in corn extract from 2.4 pg mL⁻¹ to 625 pg mL⁻¹ with a limit of detection of 2.2 pg mL⁻¹, which was approximately 15-fold lower than that of conventional HRP-based ELISA. Our developed fluorescence immunoassay was also similar to HRP-based ELISA in terms of selectivity, accuracy, and reproducibility. In summary, this study was the first to use the GOx-mediated fluorescence quenching of QDs in immunoassay to detect OTA, offering a new possibility for the analysis of other mycotoxins and biomolecules.     

Multiplex detection of tumor markers with photonic suspension array

A novel photonic suspension array was developed for multiplex immunoassay. The carries of this array were silica colloidal crystal beads (SCCBs). The codes of these carriers are the characteristic reflection peak originated from their structural periodicity, and therefore they do not suffer from fading, bleaching, quenching, and chemical instability. In addition, because no dyes or materials related with fluorescence are included, the fluorescence background of SCCBs is very low. With a sandwich format, the proposed suspension array was used for simultaneous multiplex detection of tumor markers in one test tube. The results showed that the four tumor markers, α-fetoprotein (AFP), carcinoembryonic antigen (CEA), carcinoma antigen 125 (CA 125) and carcinoma antigen 19-9 (CA 19-9) could be assayed in the ranges of 1.0-500 ng mL⁻¹, 1.0-500 ng mL⁻¹, 1.0-500 U mL⁻¹ and 3.0-500 U mL⁻¹ with limits of detection of 0.68 ng mL⁻¹, 0.95 ng mL⁻¹, 0.99 U mL⁻¹ and 2.30 U mL⁻¹ at 3σ, respectively. The proposed array showed acceptable accuracy, detection reproducibility, storage stability and the results obtained were in acceptable agreement with those from parallel single-analyte test of practical clinical sera. This technique provides a new strategy for low cost, automated, and simultaneous multiplex immunoassay.     

Highly sensitive electrogenerated chemiluminescence biosensor in profiling protein kinase activity and inhibition using a multifunctional nanoprobe

We presented a novel electrogenerated chemiluminescence (ECL) biosensor for monitoring the activity and inhibition of protein kinases based on signal amplification using enzyme-functionalized Au NPs nanoprobe. In this design, the biotin-DNA labeled glucose oxidase/Au NPs (GOx/Au NPs/DNA-biotin) nanoprobes, prepared by conjugating Au NPs with biotin-DNA and GOx, were bound to the biotinylated anti-phosphoserine labeled phosphorylated peptide modified electrode surface through a biotin−avidin interaction. The GOx assembled on the nanoprobe can catalyze glucose to generate H₂O₂ in the presence of O₂ while the ECL reaction occurred in the luminol ECL biosensor. At a higher concentration of kinase, there are more nanoprobes on the electrode, which gives a higher amount of GOx at the electrode interface and thus higher electrocatalytic efficiency to the luminol ECL reaction. Therefore, the activity of protein kinases can be monitored by ECL with high sensitivity. Protein kinase A (PKA), an important enzyme in regulation of glycogen, sugar, and lipid metabolism in the human body, was used as a model to confirm the present proof-of-concept strategy. The as-proposed biosensor presents high sensitivity, low detection limit of 0.013 U mL⁻¹, wide linear range (from 0.02 to 40 U mL⁻¹), and excellent stability. Moreover, this biosensor can also be used for quantitative analysis of kinase inhibition. On the basis of the inhibitor concentration dependent ECL signal, the half-maximal inhibition value IC₅₀ of ellagic acid, a typical PKA inhibitor, was estimated, which is in agreement with those obtained using the conventional kinase assay. The simple and sensitive biosensor is promising in developing a high-through assay of in vitro kinase activity and inhibitor screening for clinic diagnostic and drug development.     

Preparation and characterization of Prussian blue nanowire array and bioapplication for glucose biosensing

Prussian blue nanowire array (PBNWA) was prepared via electrochemical deposition with polycarbonate membrane template for effective modification of glassy carbon electrode. The PBNWA electrode thus obtained was demonstrated to have high-catalytic activity for the electrochemical reduction of hydrogen peroxide in neutral media. This enabled the PBNWA electrode to show rapid response to H₂O₂ at a low potential of −0.1 V over a wide range of concentrations from 1 × 10⁻⁷ M to 5 × 10⁻² M with a high sensitivity of 183 μA mM⁻¹ cm⁻². Such a low-working potential also substantially improved the selectivity of the PBNWA electrode against most electroactive species such as ascorbic acid and uric acid in physiological media. A detection limit of 5 × 10⁻⁸ M was obtained using the PBNWA electrode for H₂O₂, which compared favorably with most electroanalysis procedures for H₂O₂. A biosensor toward glucose was then constructed with the PBNWA electrode as the basic electrode by crosslinking glucose oxidase (GOx). The glucose biosensor allowed rapid, selective and sensitive determination of glucose at −0.1 V. The amperometric response exhibited a linear correlation to glucose concentration through an expanded range from 2 × 10⁻⁶ M to 1 × 10⁻² M, and the response time and detection limit were determined to be 3 s and 1 μM, respectively.     

Sulfonated polyaniline network grafted multi-wall carbon nanotubes for enzyme immobilization, direct electrochemistry and biosensing of glucose

A new nanomaterial was prepared by grafting a layer of sulfonated polyaniline network (SPAN-NW) on to the surface of multi-walled carbon nanotube (MWNT) and effectively utilized for immobilization of an enzyme and for the fabrication of a biosensor. SPAN-NW was formed on the surface of MWNT by polymerizing a mixture of diphenyl amine 4-sulfonic acid (DPASA), 4-vinyl aniline (VA) and 2-acrylamido-2-methyl-1-propane sulfonic acid (APASA) in the presence of amine functionalized MWNT (MWNT-NH₂). The MWNT-g-SPAN-NW was immobilized with glucose oxidase (GOx) to fabricate the SPAN-NW/GOx biosensor. MWNT-g-SPAN-NW/GOx electrode showed direct electron transfer (DET) for GOx with a fast heterogeneous electron transfer rate constant (k_s) of 4.11 s^− 1. The amperometric current response of MWNT-g-SPAN-NW/GOx biosensor shows linearity up to 9 mM of glucose, with a correlation coefficient of 0.99 and a detection limit of 0.11 μM (S/N = 3). At a low applied potential of − 0.1 V, MWNT-g-SPAN-NW/GOx electrode possesses high sensitivity (4.34 μA mM^− 1) and reproducibility towards glucose.     

Cerium oxide-deposited mesoporous silica nanoparticles for the determination of carcinoembryonic antigen in serum using inductively coupled plasma-mass spectrometry

CeO₂-deposited mesoporous silica nanoparticles were synthesized as a probe to determine carcinoembryonic antigen (CEA) in serum by inductively coupled plasma-mass spectrometry (ICP-MS). The prepared mesoporous nanoparticles were modified and tagged to the target for sandwich-type immunoassay. Fe₃O₄ magnetic nanoparticles (MNPs) were also synthesized and immobilized with antibody to extract the target biomarker. The calibration curve of the synthesized CeO₂-deposited silica nanoparticles, which was plotted by the signal ratio of ¹⁴⁰Ce/⁵⁷Fe measured by ICP-MS vs. the concentration of CEA, showed excellent linearity and sensitivity owing to the signal amplification and low spectral interference. Under optimal conditions, the sandwich-type analytical method was applied to determine CEA in serum spiked in the range of 0.001–5 ng mL⁻¹ and showed a limit of detection of 0.36 ng mL⁻¹. Since the deposited CeO₂ in the mesoporous silica layer can be substituted by other metal compounds, various kinds of metal-deposited nanoparticles can be prepared as probe materials for multiplex detection in bioanalysis.     

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.     

Modification of polypyrrole nanowires array with platinum nanoparticles and glucose oxidase for fabrication of a novel glucose biosensor

A novel glucose biosensor, based on the modification of well-aligned polypyrrole nanowires array (PPyNWA) with Pt nanoparticles (PtNPs) and subsequent surface adsorption of glucose oxidase (GOx), is described. The distinct differences in the electrochemical properties of PPyNWA–GOx, PPyNWA–PtNPs, and PPyNWA–PtNPs–GOx electrodes were revealed by cyclic voltammetry. In particular, the results obtained for PPyNWA–PtNPs–GOx biosensor showed evidence of direct electron transfer due mainly to modification with PtNPs. Optimum fabrication of the PPyNWA–PtNPs–GOx biosensor for both potentiometric and amperometric detection of glucose were achieved with 0.2 M pyrrole, applied current density of 0.1 mA cm⁻², polymerization time of 600 s, cyclic deposition of PtNPs from −200 mV to 200 mV, scan rate of 50 mV s⁻¹, and 20 cycles. A sensitivity of 40.5 mV/decade and a linear range of 10 μM to 1000 μM (R² = 0.9936) were achieved for potentiometric detection, while for amperometric detection a sensitivity of 34.7 μA cm⁻² mM⁻¹ at an applied potential of 700 mV and a linear range of 0.1–9 mM (R² = 0.9977) were achieved. In terms of achievable detection limit, potentiometric detection achieved 5.6 μM of glucose, while amperometric detection achieved 27.7 μM.