Development of isotopic and non-isotopic microwell based immunoassays for hCG using 125I and biotin labeled hCG

A novel label-free electrochemical immunosensor based on the composite of LPCs-SnS2 and AuNPs for the detection of human chorionic gonadotropin

LPCs-SnS₂ with a 3D conduction architecture was prepared by a facile hydrothermal process.

DNA-Redox Cation Interaction Improves the Sensitivity of an Electrochemical Immunosensor for Protein Detection

A simple DNA-redox cation interaction enhancement strategy has been developed to improve the sensitivity of electrochemical immunosensors for protein detection. Instead of labeling with fluorophores or redox-active groups, the detection antibodies were tethered with DNA single strands. Based on the electrostatic interaction between redox cations ([Ru(NH₃)₆]³⁺) and negatively charged DNA backbone, enhanced electrochemical signals were obtained. Human chorionic gonadotropin (hCG) detection has been performed as a trial analysis. A linear response range up to the concentration of 25 mIU/mL and a detection limit of 1.25 mIU/mL have been achieved, both are comparable with the ultrasensitive enzyme-linked immunosorbent assay (ELISA) tests. The method also shows great selectivity towards hCG over other hormones such as thyroid stimulating hormone (TSH) and follicle stimulating hormone (FSH). By and large, our approach bears the merits of cost effectiveness and simplicity of instrumentation in comparison with conventional optical detection methods.

Gel pad array chip for high throughput and multi-analyte microbead-based immunoassays

We present here a gel pad array chip for high-throughput and multi-analyte microbead-based immunoassays. The chip is fabricated by photo-patterning of two polymeric gels, polyacrylamide gel and polyethylene glycol (PEG) gel, on a glass slide. The resulting chip consists of 40 polyacrylamide gel pad array units for the immobilization of microbeads and each gel pad array is surrounded with a PEG micropillar ring to confine the samples within the microarray. As a proof of concept, this chip was tested for quantitative immunoassays for two model cancer markers, human chorionic gonadotropin (hCG) and prostate specific antigen (PSA), in serum samples. Detection limits below the physiological threshold level for cancer diagnosis were achieved with good inter- and intra-chip reproducibility. Moreover, by using spatial encoded microbeads, simultaneous detection of both hCG and PSA on each gel pad array is achieved with single filter fluorescence imaging. This gel pad array chip is easy to use, easy to fabricate with low cost materials and minimal equipment and reusable. It could be a useful tool for common biolabs to customize their own microbead array for multi-analyte immunoassays.

Asp330 and Tyr331 in the C-terminal cysteine-rich region of the luteinizing hormone receptor are key residues in hormone-induced receptor activation

The luteinizing hormone (LH) receptor plays an essential role in male and female gonadal function. Together with the follicle-stimulating hormone (FSH) and thyroid stimulating hormone (TSH) receptors, the LH receptor forms the family of glycoprotein hormone receptors. All glycoprotein hormone receptors share a common modular topography, with an N-terminal extracellular ligand binding domain and a C-terminal seven-transmembrane transduction domain. The ligand binding domain consists of 9 leucine-rich repeats, flanked by N- and C-terminal cysteine-rich regions. Recently, crystal structures have been published of the extracellular domains of the FSH and TSH receptors. However, the C-terminal cysteine-rich region (CCR), also referred to as the "hinge region," was not included in these structures. Both structure and function of the CCR therefore remain unknown. In this study we set out to characterize important domains within the CCR of the LH receptor. First, we mutated all cysteines and combinations of cysteines in the CCR to identify the most probable disulfide bridges. Second, we exchanged large parts of the LH receptor CCR by its FSH receptor counterparts, and characterized the mutant receptors in transiently transfected HEK 293 cells. We zoomed in on important regions by focused exchange and deletion mutagenesis followed by alanine scanning. Mutations in the CCR specifically decreased the potencies of LH and hCG, because the potency of the low molecular weight agonist Org 41841 was unaffected. Using this unbiased approach, we identified Asp(330) and Tyr(331) as key amino acids in LH/hCG mediated signaling.

Prostate-specific antigen detection by using a reusable amperometric immunosensor based on reversible binding and leasing of HRP-anti-PSA from phenylboronic acid modified electrode

BACKGROUND

In recent years, many automated immunoassay analyzers have been developed for accurate diagnosis of various disease states and to improve effective drug administration. Amperometric immunoassay has been increasingly applied to laboratory medicine due to its ease in automation, rapid speed and low detection limits. It is important to develop reusable immunologically-sensitive elements for prostate-specific antigen (PSA) detection.

METHODS

The strategy for the immunosensor construction is based on the enzyme-conjugated prostate-specific antibody (HRP-anti-PSA) reversible binding with a self-assembled phenylboronic acid monolayer on gold.

RESULTS

After incubating an HRP-anti-PSA modified electrode in a PSA solution, a decrease in the electrocatalytic response of the HRP-anti-PSA modified electrode to the reduction of H(2)O(2) is observed. The photometric activity assays show that this decrease of the electrocatalytic response arises from the formation of immunocomplexes of HRP-conjugated anti-PSA and its antigen, not from the loss of bound HRP-anti-PSA from the electrode surface. Analytical performances and optimal conditions of the described immunosensor are also investigated. Under the optimal conditions, the amperometric immunosensor shows a linear increase of the relative intensity in 2 PSA concentration range from 2 to 15 ng/ml and 15 to 120 ng/ml, respectively.

CONCLUSION

This method could be used for rapid analysis of PSA and potentially other antigens.

A reusable electrochemical immunosensor for carcinoembryonic antigen via molecular recognition of glycoprotein antibody by phenylboronic acid self-assembly layer on gold

A reusable amperometric immunosensor based on the reversible boronic acid-sugar interaction is proposed. The immunosensor was prepared by self-assembling a thiol-mixed monolayer comprised of conjugates of 3-aminophenylboronic acid with 11-mercaptoundecanoic acid (APBA-MUA) and 11-mercapto-1-undecanol (MU) on gold. The resulting boronic acid coating layer can specifically bind with the glycoprotein antibody, enzyme conjugated carcinoembryonic antibody (HRP-anti-CEA). Voltammetric and electrochemical impedance spectroscopic (EIS) studies and surface plasmon resonance (SPR) measurements show that the binding of HRP-anti-CEA to the APBA interface is reversible and the HRP-anti-CEA can be removed with an acidic buffer or a solution containing sorbitol. The bound enzyme-conjugated antibody can retain its enzyme catalytic activity to the reduction of hydrogen peroxide (H(2)O(2)) and its immunoactivity while binding with CEA to form an immunocomplex. After the formation of the immunocomplex, the access of the active center of HRP to thionine was partially inhibited. This leads to a linear decrease in the electrocatalytic response of HRP-anti-CEA-modified electrode over a CEA concentration range of 2.5 to 40.0 ng mL(-1). After monitoring the immunoreaction signals, the immunocomplex can be easily removed from the APBA interface with a regeneration solution. This regenerated APBA interface can rebound with HRP-anti-CEA and be recognized by the antigen, through which a reusable immunosensor with an RSD of 7.1% for four cycles can be obtained. Under optimal conditions, the detection limit for the CEA immunoassay is 1.1 ng mL(-1), at three times background noise. Serum CEA determination results, obtained with the proposed method, shows that the immunosensor has an acceptable accuracy.

Development of dual-enzyme-based simultaneous immunoassay for measurement of progesterone and human chorionic gonadotropin

The development of a simultaneous multianalyte immunoassay for the detection of progesterone and human chorionic gonadotropin (hCG) in serum is described. In this simultaneous multianalyte assay, two different enzymes, viz. horse radish peroxidase (HRP) and alkaline phosphatase (ALP), were used as markers. To the simultaneous immobilized progesterone and hCG antibody microwells, 50 microL of different concentrations of combined standards or serum samples was added in duplicate and then 100 microL of combined conjugate reagent, composed of 17-alpha-OH-P-ALP and hCG-biotin was added to all the wells and incubated for 1h at 37 degrees C. After incubation, the contents of the wells were decanted and washed thoroughly with running tap water. After washing, 100 microL alkaline phosphatase substrate along with streptavidin-horseradish peroxidase was added to all the wells and incubated for 0.5 h at 37 degrees C. After incubation, the developed color was measured at 405 nm. The absorbency at this stage provides the result for the progesterone assay. The contents of the wells were decanted and washed. In the next step, 100 microL of tetramethylbenzidene/H2O2 reagent was added to all the wells. After 15 min of incubation, 100 microL of 0.5 M H2SO4 was added to all the wells and the color was read at 450 nm. The absorbency at this stage provides the result for the hCG assay. Sensitivity of the progesterone and hCG assays were 0.118 ng/ml and 0.124 IU/ml respectively. Intra- and inter assay percentage coefficients of variation ranged from 1.8 to 7.1 and 9.1 to 11.5 for progesterone and from 2.1 to 10.4 and 7.2 to 11.3 for hCG. There was good correlation between the discrete and the simultaneous assays. For progesterone assay, R2 was 0.99 and for hCG R2 was also 0.99. The developed dual assay for progesterone and hCG may be useful for the diagnosis of abnormal pregnancies such as miscarriages and ectopic pregnancies.

Detection of human chorionic gonadotrophin hormone using a label-free epoxysilane-modified capacitive immunosensor

A new and label-free capacitive immunosensor based on antibody-functionalized epoxysilane on a glassy carbon electrode has been developed for quantitative detection of human chorionic gonadotropin (hCG). Monitoring the changes in the capacitance signals of antibodies before and after the binding of the antigen provides the basis for an immunoassay. The performance and factors influencing the immunosensor were also studied. Under the optimized conditions, the developed immunosensor quantitatively detected serum hCG in the range of 18-450 mIU/ml with a detection limit of 5.0 mIU/ml (at 3delta). Thirty-five patients' sera were assayed by the proposed immunosensor, and the results agreed with those given by the commercial radioimmunoassay test kit, with correlation coefficient of 0.998. Further research about the intrinsic electroactivity of antibodies and their target molecules would surely provide new and sensitive screening assays as well as extensive data regarding their interaction mechanisms.