A sub-picogram sensitive rapid chemiluminescent immunoassay for the detection of human fetuin A

Peptide Charge Derivatization as a Tool for Early Detection of Preeclampsia by Mass Spectrometry-A Comparison with the ELISA Test

Early detection of any preeclampsia biomarkers may lower the risk of mortality, both for a mother and a child. Our study focuses on techniques for preeclampsia biomarker identification by comparing the results of a method using liquid chromatography mass spectrometry in multiple reaction monitoring mode (LC-MS/MS) with those by the enzyme-linked immunosorbent assay (ELISA) test, as well as by comparing the obtained results with clinical data. In the proposed LC-MS/MS method a tryptic digest peptide charge derivatization strategy was used as a tool for sensitive detection of podocin, i.e., a previously discovered preeclampsia biomarker present in urine samples from pregnant women. Urine samples from pregnant women with diagnosed preeclampsia were collected at different stages of pregnancy and from healthy subjects, and then were analyzed by ELISA test and the proposed method with LC-MS/MS. Charge derivatization of the ε amino group of C-terminal lysine residues in tryptic digests by 2,4,6-triphenylpyrylium salt was performed to increase the ionization efficiency in the LC-MS/MS mode. Podocin was identified at the early stage of pregnancy, while its detection using an ELISA test was not possible. The protocol for urine sample preparation was optimized. Our results show that the proposed method by LC-MS/MS in combination with peptide charge derivatization, provides an ultrasensitive tool for diagnosis of preeclampsia, and provides earlier detection than a clinical diagnosis or ELISA test. The proposed solution may revolutionize medical diagnostics.

Evaluation of podocin in urine in horses using qualitative and quantitative methods

No sensitive method for diagnosing early kidney dysfunction in horses has been identified so far. Many studies carried out in humans and small animals show that podocin can be useful to diagnose various kidney diseases, mainly affecting the glomeruli. The aim of this study was to perform a qualitative and quantitative analysis of podocin in urine samples obtained from healthy horses, horses with clinical kidney dysfunction and horses at risk of acute kidney injury. The study objectives aimed to assess: (1) whether the selected podocin tryptic peptide for LC-MS-MRM allows for podocin detection in horse; and (2) whether the species-specific ELISA test makes this detection possible as well;, (3) whether the chosen methods are sensitive enough to detect kidney dysfunction and glomerular injury, (4) whether the results of the tests applying both methods correspond with one another, (5) whether the results correlate with the hematological and biochemical data. The signals that may indicate the presence of trypsin fragments of podocin were found in three healthy horses, all the horses diagnosed with kidney dysfunction and half of the animals at risk for acute kidney injury. The concentration of podocin, diagnosed with the ELISA test was as follows: from 0.19 to 1.2 ng/ml in healthy animals, from 0.19 to 20.0 ng/ml in AKI horses, from 0.29 to 5.71 ng/ml in horses at risk for acute kidney injury. The results of both methods corresponded significantly. Podocin may be a potential biomarker of clinical kidney disease in horses and may be used in the detection of glomerular injury. However, its use is limited by the possibility of physiological podocyturia. LC-MS-MRM seems to be a more sensitive method to evaluate the presence of podocin than the ELISA test, whilst selected tryptic peptides of podocin appear to apply to horses. The ELISA test showed greater effectiveness in excluding the disease than in confirming it.

Development of a sensitive monoclonal antibody-based sandwich ELISA to detect Vip3Aa in genetically modified crops

Objectives

To develop a sensitive monoclonal antibody-based sandwich enzyme-linked immunosorbent assay (ELISA) to detect Vip3Aa in genetically modified (GM) crops and their products.

Results

Vegetative insecticidal proteins (Vips) are secreted by Bacillus thuringiensis (Bt) and are known to be toxic to Lepidoptera species. Vip3Aa family proteins, Vip3Aa19 and Vip3Aa20, were successfully applied in GM crops to confer an effective and persistent insecticidal resistance. A sensitive monoclonal antibody-based sandwich ELISA was developed to detect Vip3Aa in GM crops and their products. Two monoclonal antibodies were raised against the overexpressed and purified His-Vip3Aa20, were purified from mouse ascites and characterized. A sandwich ELISA method was developed using the 2G3-1D7 monoclonal antibody for capture and the biotin-labeled 1F9-1F5 monoclonal antibody for detection of Vip3Aa20. The linear detection range of the method was found to be approximately 31.25–500 pg/ml, with a sensitivity of 10.24 pg/ml.

Conclusions

The established ELISA was effective for detecting Vip3Aa family proteins other than Vip3Aa8, and was successfully applied in the detection of Vip3Aa20 and Vip3Aa19 expressed in transgenic maize and cotton.

Versatile antifouling coatings based on self-assembled oligopeptides for engineering and biological materials

The existence of nonspecific protein adsorption often results in significant challenges for microfluidic devices and laboratory cultureware used in biological experiments.

Emerging Human Fetuin A Assays for Biomedical Diagnostics

Human fetuin A (HFA) plays a prominent pathophysiological role in numerous diseases and pathophysiological conditions with considerable biomedical significance; one example is the formation of calciprotein particles in osteoporosis and impaired calcium metabolisms. With impressive advances in in vitro diagnostic assays during the last decade, ELISAs have become a workhorse in routine clinical diagnostics. Recent diagnostic formats involve high-sensitivity immunoassay procedures, surface plasmon resonance, rapid immunoassay chemistries, signal enhancement, and smartphone detection. The current trend is toward fully integrated lab-on-chip platforms with smartphone readouts, enabling health-care practitioners and even patients to monitor pathological changes in biomarker levels. This review provides a critical analysis of advances made in HFA assays along with the challenges and future prospects.

Development of a double-antibody sandwich ELISA for rapid detection of Bacillus Cereus in food

Bacillus cereus is increasingly recognized as one of the major causes of food poisoning in the industrialized world. In this paper, we describe a sensitive double-antibody sandwich enzyme-linked immunosorbent assay (ELISA) that was developed for rapid detection of B. cereus in food to minimize the risk of contamination. The polyclonal antibody (pAb) and monoclonal antibodies (mAbs) specific to B. cereus were generated from rabbit antiserum and mouse ascites, respectively, using the octanoic acid/saturated ammonium sulfate precipitation method and protein A-sepharose columns. IgG-isotype mAbs were specially developed to undergo a novel peripheral multiple sites immunization for rapid gain of hybridomas and a subtractive screen was used to eliminate cross reactivity with closely related species such as Bacillus thuringiensis, B. subtilis, B. licheniformis and B. perfringens. The linear detection range of the method was approximately 1 × 10⁴–2.8 × 10⁶ cells/mL with a detection limit (LOD) of 0.9 × 10³ cells/mL. The assay was able to detect B. cereus when the samples were prepared in meat with various pathogens. The newly developed analytical method provides a rapid method to sensitively detect B. cereus in food specimens.

Biotin-Streptavidin Competition Mediates Sensitive Detection of Biomolecules in Enzyme Linked Immunosorbent Assay

Enzyme Linked Immunosorbent Assay (ELISA) is the gold standard assay for detecting and identifying biomolecules using antibodies as the probe. Improving ELISA is crucial for detecting disease-causing agents and facilitating diagnosis at the early stages of disease. Biotinylated antibody and streptavidin-conjugated horse radish peroxide (streptavidin-HRP) often are used with ELISA to enhance the detection of various kinds of targets. In the present study, we used a competition-based strategy in which we pre-mixed free biotin with streptavidin-HRP to generate high-performance system, as free biotin occupies some of the biotin binding sites on streptavidin, thereby providing more chances for streptavidin-HRP to bind with biotinylated antibody. ESAT-6, which is a protein secreted early during tuberculosis infection, was used as the model target. We found that 8 fM of free biotin mixed with streptavidin-HRP anchored the higher detection level of ESAT-6 by four-fold compared with detection without free biotin (only streptavidin-HRP), and the limit of detection of the new method was 250 pM. These results suggest that biotin-streptavidin competition can be used to improve the diagnosis of analytes in other types of sensors.

Aptamer-based 'point-of-care testing'

Aptamers are single-stranded oligonucleotides that can be artificially generated by a method called Systematic evolution of ligands by exponential enrichment (SELEX). The generated aptamers have been assessed for high-performance sensing applications due to their appealing characteristics. With either aptamers alone or complementing with antibodies, several high sensitive and portable sensors have been demonstrated for use in 'point-of-care testing'. Due to their high suitability and flexibility, aptamers are conjugated with nanostructures and utilized in field applications. Moreover, aptamers are more amenable to chemical modifications, making them capable of utilization with most developed sensors. In this overview, we discuss novel, portable, and aptamer-based sensing strategies that are suitable for 'point-of-care testing'.

Surface plasmon resonance-based immunoassay for human fetuin A

This article describes a highly-sensitive surface plasmon resonance (SPR)-based immunoassay (IA) for human fetuin A (HFA), a specific biomarker for atherosclerosis and hepatocellular carcinoma. The assay is based on a novel immobilization procedure that simply involves the dilution of an anti-HFA capture antibody (Ab) in 1% (v/v) 3-aminopropyltriethoxysilane (APTES), followed by its dispensing on a KOH-treated gold (Au)-coated SPR chip and incubation for 30 min. The developed SPR IA detected 0.3-20 ng mL(-1) of HFA with a limit of detection and sensitivity of 0.7 ng mL(-1) and 1 ng mL(-1), respectively. The highly-simplified Ab immobilization procedure is also 5-fold more rapid than conventional procedures. It leads to the leach-proof binding of the capture Ab, which means that the developed SPR IA is highly cost-effective, as the Ab-bound SPR chip could be reused for many repeated HFA IAs after regeneration with 10 mM glycine-HCl, pH 2.0. The Ab-bound SPR chip, stored at 4 °C, lost only 18% of its original activity after 4 months. For the detection of HFA spiked in diluted human whole blood and plasma, the results obtained by the developed SPR IA agreed well with the commercial HFA sandwich ELISA.

Simultaneous detection of forbidden chemical residues in milk using dual-label time-resolved reverse competitive chemiluminescent immunoassay based on amine group functionalized surface

In this study, a sensitive dual-label time-resolved reverse competitive chemiluminescent immunoassay was developed for simultaneous detection of chloramphenicol (CAP) and clenbuterol (CLE) in milk. The strategy was performed based on the distinction of the kinetic characteristics of horseradish peroxidase (HRP) and alkaline phosphatase (ALP) in chemiluminesecence (CL) systems and different orders of magnitude in HRP CL value for CAP and ALP CL value for CLE in the chemiluminescent immunoassay. Capture antibodies were covalently bound to the amine group functionalized chemiluminescent microtiter plate (MTP) for efficient binding of detection antibodies for the enzymes labeled CAP (HRP-CAP) and CLE (ALP-CLE). The CL signals were recorded at different time points by the automatic luminometers with significant distinction in the dynamic curves. When we considered the ALP CL value (about 10(5)) of CLE as background for HRP CL signal value (about 10(7)) of CAP, there was no interaction from ALP CL background of CLE and the differentiation of CAP and CLE can be easily achieved. The 50% inhibition concentration (IC50) values of CAP and CLE in milk samples were 0.00501 µg L(-1) and 0.0128 µg L(-1), with the ranges from 0.0003 µg L(-1) to 0.0912 µg L(-1) and from 0.00385 µg L(-1) to 0.125 µg L(-1), respectively. The developed method is more sensitive and of less duration than the commercial ELISA kits, suitable for simultaneous screening of CAP and CLE.

Gold nanoparticle-based enzyme-linked antibody-aptamer sandwich assay for detection of Salmonella Typhimurium

Enzyme-linked immunosorbent assay (ELISA) provides a convenient means for the detection of Salmonella enterica serovar Typhimurium (STM), which is important for rapid diagnosis of foodborne pathogens. However, conventional ELISA is limited by antibody-antigen immunoreactions and suffers from poor sensitivity and tedious sample pretreatment. Therefore, development of novel ELISA remains challenging. Herein, we designed a comprehensive strategy for rapid, sensitive, and quantitative detection of STM with high specificity by gold nanoparticle-based enzyme-linked antibody-aptamer sandwich (nano-ELAAS) method. STM was captured and preconcentrated from samples with aptamer-modified magnetic particles, followed by binding with detector antibodies. Then nanoprobes carrying a large amount of reporter antibodies and horseradish peroxidase molecules were used for colorimetric signal amplification. Under the optimized reaction conditions, the nano-ELAAS assay had a quantitative detection range from 1 × 10(3) to 1 × 10(8) CFU mL(-1), a limit of detection of 1 × 10(3) CFU mL(-1), and a selectivity of >10-fold for STM in samples containing other bacteria at higher concentration with an assay time less than 3 h. In addition, the developed nanoprobes were improved in terms of detection range and/or sensitivity when compared with two commercial enzyme-labeled antibody signal reporters. Finally, the nano-ELAAS method was demonstrated to work well in milk samples, a common source of STM contamination.

One-step antibody immobilization-based rapid and highly-sensitive sandwich ELISA procedure for potential in vitro diagnostics

An improved enzyme-linked immunosorbent (ELISA) assay using one-step antibody immobilization has been developed for the detection of human fetuin A (HFA), a specific biomarker for atherosclerosis and hepatocellular carcinoma. The anti-HFA formed a stable complex with 3-aminopropyltriethoxysilane (APTES) by ionic and hydrophobic interactions. The complex adsorbed on microtiter plates exhibited a detection range of 4.9 pg mL(-1) to 20 ng mL(-1) HFA, with a limit of detection of 7 pg mL(-1). Furthermore, an analytical sensitivity of 10 pg mL(-1) was achieved, representing a 51-fold increase in sensitivity over the commercial sandwich ELISA kit. The results obtained for HFA spiked in diluted human whole blood and plasma showed the same precision as the commercial kit. When stored at 4°C in 0.1 M phosphate-buffered saline (PBS, pH 7.4), the anti-HFA bound microtiter plates displayed no significant decrease in their functional activity after two months. The new ELISA procedure was extended for the detection of C-reactive protein, human albumin and human lipocalin-2 with excellent analytical performance.

Plasma fetuin-A levels are reduced in patients with hypothyroidism

OBJECTIVE

To determine plasma fetuin-A levels in hypothyroid patients before and after treatment with l-thyroxine (T4) and to determine the relation between plasma fetuin-A levels with cardiovascular risk factors.

DESIGN

A prospective, controlled, single-blind study.

METHODS

Forty-four treatment-naive female patients diagnosed with hypothyroidism and 39 age- and sex-matched control subjects were enrolled. Anthropometric measurements, blood pressure, plasma TSH, fetuin-A, free T4, LDL-cholesterol, triglyceride, C-reactive protein, fibrinogen levels, and brachial artery flow-mediated dilatation were measured. All measurements were repeated after 3 months in the control group and 3 months after the attainment of euthyroidism with l-T4 replacement in the hypothyroid group. Baseline data were compared between the two groups. Posttreatment plasma fetuin-A levels of hypothyroid patients were compared with baseline levels of both groups. The relationship between plasma fetuin-A, TSH levels, and other cardiovascular risk factors was evaluated.

RESULTS

Plasma fetuin-A levels were ∼20% lower in hypothyroid female patients compared with the controls (P=0.0001). Fetuin-A levels increased by ∼20% in hypothyroid patients after achievement of euthyroidism (P=0.0001) and were no longer different compared with controls (P=0.38). There was a negative correlation between plasma TSH and fetuin-A levels (r=-0.79; P=0.001). There was no significant correlation between plasma fetuin-A levels and cardiovascular risk factors within or between groups. The fetuin-A levels were normalized with thyroid hormone treatment.

CONCLUSION

Plasma fetuin-A levels are reduced in female patients with hypothyroidism, which are restored to normal during restoration of euthyroidism. There was no relation with cardiovascular risk factors.