A designer ormosil gel for preparation of sensitive immunosensor for carcinoembryonic antigen based on simple direct electron transfer

Antibody-Electroactive Probe Conjugates Based Electrochemical Immunosensors

Suitable immobilization of a biorecognition element, such as an antigen or antibody, on a transducer surface is essential for development of sensitive and analytically reliable immunosensors. In this review, we report on (1) methods of antibody prefunctionalization using electroactive probes, (2) methods for immobilization of such conjugates on the surfaces of electrodes in electrochemical immunosensor construction and (3) the use of antibody-electroactive probe conjugates as bioreceptors and sensor signal generators. We focus on different strategies of antibody functionalization using the redox active probes ferrocene (Fc), anthraquinone (AQ), thionine (Thi), cobalt(III) bipyridine (Co(bpy)33+), Ru(bpy)32+ and horseradish peroxidase (HRP). In addition, new possibilities for antibody functionalization based on bioconjugation techniques are presented. We discuss strategies of specific, quantitative antigen detection based on (i) a sandwich format and (ii) a direct signal generation scheme. Further, the integration of different nanomaterials in the construction of these immunosensors is presented. Lastly, we report the use of a redox probe strategy in multiplexed analyte detection.

Nano-Based PSA Biosensors: An Early Detection Technique of Prostate Cancer

Prostate-specific antigen or PSA is a protein biomarker which is produced by the cells of prostate gland. The normal level of PSA in blood is often elevated in men with prostate cancer. In India, prostate cancer is one among the five, mostly cited cancer in men and it is getting increased by 1% every year. The screening test used for prostate cancer is the Prostate Specific Antigen test. The first PSA assay was determined in 1979. Most of the current techniques used for PSA detection are utilizing large analyzers, there by increased time and cost. Increased PSA levels can also because of prostatitis (inflammation of the prostate gland) or due to many other reasons. A proper technique to differential diagnose this disease is also an issue. The benchmark for the PSA level cannot be determined accurately. For this, various types of biosensors are used. This review journal is is trying to analyze variouus Nano-Biosensors used for early detection of PSA from blood in an early stage itself.

A dual amplification strategy for ultrasensitive electrochemiluminescence immunoassay based on a Pt nanoparticles dotted graphene–carbon nanotubes composite and carbon dots functionalized mesoporous Pt/Fe

A facile and sensitive ECL immunosensor has been designed using Pt/Gr–CNTs as a platform and Pt/Fe@CDs as bionanolabels.

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.

Electrochemical immunoassay of carcinoembryonic antigen based on TiO2–graphene / thionine / gold nanoparticles composite

A novel multilayer film based on gold nanoparticles (AuNPs), thionine (Thi), and TiO2–graphene (TiO2–Gr) was exploited to develop a highly sensitive amperometric immunosensor for detecting carcinoembryonic antigen (CEA). Firstly, Nafion–TiO2–Gr homogeneous composite was dropped on the surface of a glassy carbon electrode (GCE). Then Thi was chemisorbed by the TiO2–Gr–Nafion composite. Furthermore, the negative ly charged AuNPs were chemisorbed onto Thi film through the electrostatic force with the amino groups of Thi. Cyclic voltammetry (CV) was employed to characterize the assembly process and the performance of the immunosensor. Because of the synergistic effect of the AuNPs, Thi, and the unique properties of TiO2–Gr, the obtained immunosensor exhibited a wide linear response to CEA in two ranges from 0.1 to 10.0 ng mL−1 and from 10.0 to 120.0 ng mL−1 with a relatively low detection limit of 0.01 ng mL−1 (S/N = 3), as well as good stability and repeatability.

A novel label-free amperometric immunosensor for carcinoembryonic antigen based on redox membrane

A label-free immunosensor was developed to detect the presence of an antigen. This immunosensor was based on the modulation of the electrochemistry of the surface bound redox species K(3)Fe(CN)(6) (FC). The model antigen was carcinoembryonic antigen (CEA) and the model epitope was the antibody of CEA (anti-CEA). Glassy carbon (GC) electrode surfaces were first drop-coated with a mixture of FC and chitosan and air-dried. The electrode surface was then covered with nafion membrane, which contained gold nanoparticles. After binding with polyethyleneimine (PEI), glutaraldehyde (GA) was used to cross-link PEI and anti-CEA. Binding of CEA to the surface bound epitope resulted in attenuation of the FC electrochemistry. Under optimal conditions, the response of the label-free immunosensor had a linear range of 0.01-150 ng mL(-1) with a detection limit of 3 pg mL(-1) (S/N = 3). Its response was better than those of radioimmunoassays, enzyme-linked immunosorbent assays, and chemiluminescence assays.

Electrochemical immunoassay of carcinoembryonic antigen based on a lead sulfide nanoparticle label

We describe a lead sulfide nanoparticle (PbS NP)-based electrochemical immunoassay to detect a tumor biomarker, carcinoembryonic antigen (CEA). Cubic PbS NPs were prepared and functionalized with thioglycolic acid (TGA), which stabilized the formed NPs and offered carboxyl groups to conjugate with CEA antibodies. PbS NP conjugated with monoclonal CEA antibody was used as a label in an immunorecognition event. After a complete sandwich immunoreaction among the primary CEA antibody (immobilized on the carboxyl-modified magnetic beads), CEA and the PbS-labeled secondary antibody (PbS-anti-CEA), PbS labels were captured to the magnetic-bead (MB) surface through the antibody-antigen immunocomplex. Electrochemical stripping analysis of the captured PbS was used to quantify the concentration of CEA after an acid-dissolution step. The MBs and the magnetic separation platform were used to integrate a facile antibody immobilization with immunoreactions and the isolation of immunocomplexes from reaction solutions in the immunoassay. The voltammetric response is highly linear over the range of 1-50 ng ml(-1) CEA, and the limit of detection is estimated to be 0.5 ng ml(-1). The performance of this nanoparticle-based electrochemical immunoassay was successfully evaluated with human serum spiked with CEA, indicating that this convenient and sensitive technique offers great promise for rapid, simple and cost-effective analysis of tumor biomarkers in biological fluids.

Disposable Reagentless Electrochemical Immunosensor Array Based on a Biopolymer/Sol-Gel Membrane for Simultaneous Measurement of Several Tumor Markers

Background: A reagentless sensor array for simultaneous multianalyte testing (SMAT) may enable accurate diagnosis and be applicable for point-of-care testing. We developed a disposable reagentless immunosensor array for simple immunoassay of panels of tumor markers.

Methods: We carried out SMAT with a direct capture format, in which colloidal gold nanoparticles with bound horseradish peroxidase (HRP)-labeled antibodies were immobilized on screen-printed carbon electrodes with biopolymer/sol-gel to trap their corresponding antigens from sample solution. Upon formation of immunocomplex, the direct electrochemical signal of the HRP decreased owing to increasing spatial blocking, and the analytes could be simultaneously determined by monitoring the signal changes.

Results: The proposed reagentless immunosensor array allowed simultaneous detection of carcinoma antigen 153, carcinoma antigen 125, carbohydrate antigen 199, and carcinoembryonic antigen in clinical serum samples in the ranges of 0.4–140 kU/L, 0.5–330 kU/L, 0.8–190 kU/L, and 0.1–44 μg/L, respectively, with detection limits of 0.2 kU/L, 0.5 kU/L, 0.3 kU/L, and 0.1 μg/L corresponding to the signals 3 SD above the mean of a zero standard. The interassay imprecision of the arrays was <9.5%, and they were stable for 35 days. The positivity detection rate of panels of tumor markers was >95.5% for 95 cases of cancer-positive sera.

Conclusions: The immunosensor array provides a SMAT with short analytical time, small sampling volume, no need for substrate, and, no between-electrode cross-talk. This method not only proved the capability of the array in point-of-care testing, but also allowed simultaneous testing of several tumor markers.

Organically modified silica: synthesis and applications due to its surface interaction with organic molecules

Silica gels can be chemically modified using organic precursors producing organically modified silica (ORMOSIL), a class of novel materials for hosting varieties of organic and inorganic substrates. Ormosil matrixed materials show an enhanced activity during catalysis, photochemical activities like absorption and emission, electrochemical sensitivities, sensing of gases, solvents, pH of solution and biomolecules, etc. Ormosil-based materials can be used as efficient protective coatings and can be utilized in designing wave guides that can carry out excellent photonic transmission of information. The synthetic and chemical modification of ormosil and some of the above applications have been discussed.