Creation of a quick and sensitive fluorescent immunosensor for detecting the mineralocorticoid steroid hormone aldosterone

Aldosterone (ALD) is a steroid hormone secreted by the zona glomerulosa of the adrenal cortex that mainly acts on the kidney to regulate sodium ion and water reabsorption. Detection of ALD plays an important role in the diagnosis of primary aldosteronism in patients with hypertension. For the first time, the gene encoding the anti-ALD antibody, A2E11, was successfully cloned and analyzed using phage display technology. The antibody had an affinity of 2.5 nM against ALD, and after binding to ALD, it reached saturation within 5 s. Using this antibody, a Quenchbody (Q-body) was constructed by labeling the N-termini of heavy and light chains of the antigen-binding fragment of A2E11 with the fluorescent dye ATTO520 to detect ALD based on the principle of photoinduced electron transfer. The sensor detected ALD in 2 min, and the limit of detection was 24.1 pg/mL with a wide detection range from 24.1 pg/mL to 10 µg/mL and a half-maximal effective concentration of 42.3 ng/mL. At the highest concentration of ALD in the assay, the fluorescence intensity increased by 5.0-fold compared to the original fluorescence intensity of the Q-body solution. The Q-body could be applied to analyze 50% of human serum without a significant influence of the matrix. The recoveries of ALD in spiked serum samples with the Q-body assay were confirmed to range from 90.3% to 98.2%, suggesting their potential applications in the diagnosis of diseases, such as essential hypertension.

Isolation of a Monoclonal Antibody and its Derived Immunosensor for Rapid and Sensitive Detection of 17β-Estradiol

Estrogens are effective for stimulating several functions in living organisms and for regulating cancer development by promoting cell proliferation. Estradiol can disrupt the reproductive and endocrine systems, leading to the development of various diseases. In this study, the monoclonal antibody ESC9 was developed by immunizing mice with a 17β-estradiol (E2) conjugate, preparing an antibody phage display library, and screening monoclonal antibodies from the prepared library. An antibody with the same sequence as that of ESC9 has not been reported previously. The equilibrium dissociation constant between ESC9 and E2 was found to be 43.3 nM. Additionally, we generated an ESC9-derived immunosensor named as the ESC9 Quenchbody (Q-body), which can rapidly and sensitively detect E2. The assay can be completed within 2 min with a limit of detection of 3.9 pg/ml and half-maximal effective concentration of 154.0 ng/ml. Serum E2 levels were measured using the ESC9 Q-body without pretreatment with serum and with a high recovery rate of 83.3–126.7%. The Q-body immunosensor shows potential for clinical applications based on its excellent detection speed and sensitivity.

An Open Sandwich Immunochromatography for Non-competitive Detection of Small Antigens

Immunochromatography assay is an easy and rapid on-site detection method. However, conventional sandwich immunochromatographies using two antibodies can only detect target molecules above a threshold size. Small molecules below 1000 in molecular weight are usually detected using competitive immunoassay. However, competitive immunoassay is not suitable for visual detection of low concentration samples. Based on the principles of open sandwich immunoassay, which detects small molecules via interchain interaction of separated variable region fragments (V_H and V_L) from a single antibody, we developed non-competitive open sandwich immunochromatography. Bone Gla protein (BGP)-C7, a peptide containing the seven C-terminal amino acids of human osteocalcin, was selected as the target. By using V_L fragments fixed on a nitrocellulose membrane, and colored cellulose bead-labeled V_H fragments, we specifically detected 10 ng/mL of BGP-C7. This is the first report of open sandwich immunochromatography, which is an easy and rapid method for on-site, signal-on detection of small molecules.

A novel murine antibody and an open sandwich immunoassay for the detection of clenbuterol

Clenbuterol (CLEN) is a sympathomimetic amine used as a decongestant and bronchodilator while treating breathing disorders. It is also used in food-producing animals as it improves the rate of red meat production. However, it is prohibited in many countries nowadays due to human health and safety concerns. Unfortunately, the illegal use of CLEN is still rampant. Thus, monitoring it in food and livestock is important. Here, we report a novel murine antibody and an open sandwich enzyme linked immunosorbent assay (OS-ELISA) to detect CLEN based on antigen-antibody reactions. The genes of antibody variable regions in mice immunized with CLEN conjugated with bovine serum albumin were cloned into a phagemid (pDong1/Fab) to construct a phage-display antibody library, from which a novel antibody, A12, was selected. Then, an OS-ELISA was developed to detect CLEN using separated variable regions of the A12 antibody. The limit of detection of the assay was found to be 8 ng/mL, which was useful for monitoring CLEN usage.

Homogeneous Noncompetitive Luminescent Immunodetection of Small Molecules by Ternary Protein Fragment Complementation

The homogeneous immunological detection of small molecules at high sensitivity is still a daunting task. Here, we tried sensitive noncompetitive detection of small peptides based on the open-sandwich immunoassay principle, which was combined with a bioluminescent protein-fragment complementation assay (PCA) in vitro. Since the detection of antigen-induced approximation of the two antibody variable region fragments V_H and V_L by the standard Nanoluc-based PCA utilizing larger (LgBiT) and shorter (SmBiT) fragments was not successful, we decided to further split LgBiT into two, yielding smaller N-terminal derivative (LnBiT) and two C-terminal, 11 residue peptides (LcBiT and SmBiT) corresponding to consecutive beta strands, to which V_H and V_L were each fused and expressed in Escherichia coli cells. Through the optimization of reaction conditions and peptide sequence, the antigen osteocalcin peptide can be noncompetitively detected with a low background signal and limit of detection, yielding a high light emission of 88% compared to that of the wild-type enzyme. Since the luminescence of this open sandwich bioluminescent immunoassay (OS-BLIA) can be observed with the naked eye, it could become the foundation of many point-of-care detection systems.

Noncompetitive homogeneous immunodetection of small molecules based on beta-glucuronidase complementation

Small molecules can be sensitively detected with a positive signal by just mixing and measuring the β-glucuronidase activity within 20 min.

Detection of small molecule diagnostic markers with phage-based open-sandwich immuno-PCR

Open sandwich immunoassay (OS-IA) utilizes antigen-dependent stabilization of antibody variable region to quantify various antigens, enabling noncompetitive detection of small molecules with a broad working range. To further improve its detection sensitivity, here we employed phage-based immuno-PCR approach, wherein OS-IA and quantitative PCR methodologies were combined with the use of immobilized V(L) fusion protein and filamentous phages displaying V(H) fragment, whose DNA was extracted for PCR amplification. This approach significantly enhanced the assay sensitivity for small molecule antigens osteocalcin (BGP) peptide and 17beta-estradiol.

Adiponectin self-regulates its expression and multimerization in adipose tissue: an autocrine/paracrine mechanism?

Adiponectin, a 30-kDa peptide hormone discovered in the mid 1990s, is secreted abundantly and exclusively by adipose tissue. Adiponectin exists in three major forms: a low molecular weight (LMW) trimer, a medium molecular weight (MMW) hexamer, and a high molecular weight (HMW) 18-36 oligomer. The HMW oligomer has the most potent insulin-sensitizing activity therefore impaired adiponectin multimerization may lead to impaired glycemic control. Decreased ratio of HMW/total adiponectin has been observed in patients with obesity, type-2 diabetes mellitus, cardiovascular diseases and insulin resistance-related metabolic syndrome. Previous studies have indicated that berberine or aminoimidazole carboxamide ribonucleotide (AICAR)-induced activation of AMP-activated protein kinase (AMPK) suppresses the expression of adiponectin but promotes adiponectin multimerization in adipocytes. Since adiponectin activates AMPK through adiponectin receptors (AdipoRs) in the membranes of adipocytes, we speculate that adiponectin self-regulates its expression and multimerization in adipose tissue. The hypothesis suggests a potential drug target for treating insulin resistance and provides new interpretation of several clinical observations. In addition, we propose a rapid method for one-step detection of the distribution of adiponectin oligomers in approximately 30 min, based on the open sandwich immunoassay and fluorescence resonance energy transfer technology. With the development of this new method, the ratio of HMW/total adiponectin may be applied in clinical diagnosis as a novel biomarker for insulin resistance and metabolic disorders.