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Concept: Magnetic immunoassay


A novel enzyme-linked immunosorbent assay based on magnetic nanoparticles and biotin/streptavidin-HRP (MNP-bsELISA) was developed for rapid and sensitive detection of zearalenone (ZEN). The detection signal was enhanced and the sensitivity of the assay was improved by combined use of antibody-conjugated magnetic nanoparticles and biotin-streptavidin system. Under the optimized conditions, the regression equation for quantification of ZEN was y = -0.4287x + 0.3132 (R² = 0.9904). The working range was 0.07-2.41 ng/mL. The detection limit was 0.04 ng/mL and IC50 was 0.37 ng/mL. The recovery rates of intra-assay and inter-assay ranged from 92.8%-111.9% and 91.7%-114.5%, respectively, in spiked corn samples. Coefficients of variation were less than 10% in both cases. Parallel analysis of cereal and feed samples showed good correlation between MNP-bsELISA and liquid chromatograph-tandem mass spectrometry (R² = 0.9283). We conclude that this method is suitable for rapid detection of zearalenone in cereal and feed samples in relevant laboratories.

Concepts: Nanoparticle, Nanotechnology, ELISA, ELISPOT, Assay, Immunoassay, Magnetic nanoparticles, Magnetic immunoassay


Enzyme-linked immunosorbent assays (ELISA) are being used extensively for the identification of Bt-protein in Bt transgenic crops. A sandwich ELISA test is the most preferable immunoassay for the quantification of Bt-protein in transgenic cotton plants. Here, we describe development of sandwich ELISA, employing polyclonal rabbit antibody as a capture antibody and HRP-labeled mouse anti-Bt protein-antibody as a detector antibody.

Concepts: Antibody, ELISA, ELISPOT, Assay, Immunoassay, Multiplex, Magnetic immunoassay


Method of highly sensitive registration of magnetic nanoparticles by their non-linear magnetization is used in a novel sandwich-type immunoassay for detection of staphylococcal toxins in complex media of virtually any volume, with increasing sensitivity at higher sample volume. The signal is read out from the entire volume of a non-transparent 3D fiber structure employed as a solid phase, which provides large reaction surface, quick reagent mixing as well as antigen immunofiltration directly in the course of the assay. The method has demonstrated near-linear dose-response curves within wide range of ~3 decades while detection of staphylococcal enterotoxin A (SEA) and toxic shock syndrome toxin (TSST) in neat milk without sample preparation. The limits of detection (LOD) as low as 4 and 10 pg/mL for TSST and SEA, respectively, were obtained in 2-hour format using 30-mL samples. The second, 25-minute format, showed the LOD of 0.1 and 0.3 ng/mL for the same toxins in a 150 µL sample. The developed immunoassay can be applied in food safety control, in vitro diagnostics and veterinary for a variety of research from express tests in the field to highly sensitive laboratory tests.

Concepts: Magnetic field, Staphylococcus aureus, Streptococcus pyogenes, ELISA, Toxic shock syndrome, Exotoxin, Necrotizing fasciitis, Magnetic immunoassay


The aim of the study was to evaluate the adequacy of enzyme-linked immunosorbent assay (ELISA) in the post-exposure determination of the β-agonists clenbuterol and salbutamol in animal plasma and serum. Experimental guinea pigs (n = 20) were treated with two doses (0.25 and 2.5 mg/kg) of clenbuterol (n = 10) and salbutamol (n = 10) for seven days, whereas the control animal group (n = 10) was left untreated. Validation of the applied method yielded acceptable recovery (mean > 70%) and repeatability rates, showing ELISA to be applicable for the semi-quantitative determination of both analytes in both matrices, preferably in plasma. In both matrices, clenbuterol concentrations were proven to be significantly (14-fold) higher than those of salbutamol. Concentrations of both analytes were higher in plasma than in serum. The application of a 10-fold higher clenbuterol and salbutamol dose (2.5 mg/kg) resulted in concentrations 3- to 4-fold higher for clenbuterol and 2- to 3-fold higher for salbutamol, indicating a different release rate of these two β-agonists.

Concepts: Antibody, ELISA, ELISPOT, Assay, Eva Engvall, Immunoassay, Multiplex, Magnetic immunoassay


The ELISA is the mainstay for sensitive and quantitative detection of protein analytes. Despite its utility, ELISA is time-consuming, resource-intensive, and infrastructure-dependent, limiting its availability in resource-limited regions. Here, we describe a self-contained immunoassay platform (the “D4 assay”) that converts the sandwich immunoassay into a point-of-care test (POCT). The D4 assay is fabricated by inkjet printing assay reagents as microarrays on nanoscale polymer brushes on glass chips, so that all reagents are “on-chip,” and these chips show durable storage stability without cold storage. The D4 assay can interrogate multiple analytes from a drop of blood, is compatible with a smartphone detector, and displays analytical figures of merit that are comparable to standard laboratory-based ELISA in whole blood. These attributes of the D4 POCT have the potential to democratize access to high-performance immunoassays in resource-limited settings without sacrificing their performance.

Concepts: Protein, Blood, ELISA, Assay, Printing, Ink, Immunoassay, Magnetic immunoassay


It is difficult to discriminate healthy subjects and patients with Parkinson disease (PD) or Parkinson disease dementia (PDD) by assaying plasma α-synuclein because the concentrations of circulating α-synuclein in the blood are almost the same as the low-detection limit using current immunoassays, such as enzyme-linked immunosorbent assay. In this work, an ultra-sensitive immunoassay utilizing immunomagnetic reduction (IMR) is developed. The reagent for IMR consists of magnetic nanoparticles functionalized with antibodies against α-synuclein and dispersed in pH-7.2 phosphate-buffered saline. A high-Tc superconducting-quantum-interference-device (SQUID) alternative-current magnetosusceptometer is used to measure the IMR signal of the reagent due to the association between magnetic nanoparticles and α-synuclein molecules.

Concepts: Antibody, Magnetic field, ELISA, ELISPOT, Assay, Immunoassay, Multiplex, Magnetic immunoassay


The 42 amino acid form of amyloid-β (Aβ42) plays a key role in the pathogenesis of Alzheimer’s disease (AD) and is a core biomarker for the diagnosis of AD. Numerous studies have shown that cerebrospinal fluid (CSF) Aβ42 concentrations are decreased in AD, when measured by enzyme-linked immunosorbent assay (ELISA) and other conventional immunoassays. While most studies report no change in plasma Aβ42, independent studies using the immunomagnetic reduction (IMR) technique report an increase in plasma Aβ42 levels in AD. To confirm the opposite changes of Aβ42 levels in CSF and plasma for AD, we assayed the levels of Aβ42 in plasma of subjects with known CSF Aβ42 levels. In total 43 controls and 63 AD patients were selected at two sites: the VU University Medical Center (n = 55) and Sahlgrenska University Hospital (n = 51). IMR and ELISA were applied to assay Aβ42 in plasma and CSF, respectively. We found a moderately negative correlation between plasma and CSF Aβ42 levels in AD patients (r = -0.352), and a weakly positive correlation in controls (r = 0.186). These findings further corroborate that there are opposite changes of Aβ42 levels in CSF and plasma in AD. The possible causes for the negative correlation are discussed by taken assay technologies, Aβ42 transport from brain to peripheral blood, and sample matrix into account.

Concepts: Antibody, ELISA, ELISPOT, Assay, Eva Engvall, Immunoassay, Multiplex, Magnetic immunoassay


In this work, a low-cost PDMS micro-pump and -valve have been designed and developed to control multiple reagents for enzyme-linked immunosorbent assay (ELISA) on a programmable lab-on-a-chip (LOC) platform. The micro pump and valves were precisely controlled by selectively pressurizing the PDMS channels and chamber to actuate the multiple reagents in a controlled manner. Selective pressurizing of the PDMS structures was initiated by a simple system that maneuvered a single roller bar operated by a programmed microprocessor. The performance of the micro-pump was fully characterized and a minimum fluid volume of 1 μL was controlled. Also, the on-chip microvalves were programmed to flow the multiple reagents to automatically process the multi-step ELISA procedures. By applying the proposed platform, 19.40 pg ml-1 cardiac troponin T (cTnT) was successfully detected on the LOC device by using multiple programmed valves as multiple steps of the enzyme-linked sandwich immunoassay. As a result, the developed micro-pump and -valve, which were successfully applied to actuate a series of solutions in a controlled manner, can be widely applied to lab-on-a-chip based bioassays.

Concepts: ELISA, ELISPOT, Assay, Troponin, Eva Engvall, Immunoassay, Magnetic immunoassay, Radioimmunoassay


Measuring alpha-defensin concentrations in synovial fluid may help to diagnose periprosthetic joint infection (PJI). There are two commercially available methods for measuring alpha-defensin in synovial fluid: the enzyme-linked immunosorbent assay-based Synovasure® alpha-defensin immunoassay, which gives a numeric readout within 24 hours, and the Synovasure lateral flow test, which gives a binary readout within 20 minutes. There is no compilation of the existing literature to support the use of one of these two tests over the other.

Concepts: Diagnosis, Fluid dynamics, Measurement, Medical tests, Test method, Immunoassay, Lateral flow test, Magnetic immunoassay


A new photoluminescence (PL) enzyme immunoassay was designed for sensitive detection of aflatoxin B1(AFB1) via an innovative enzyme substrate, 6-aza-2-thiothymine-stabilized gold nanocluster (AAT-AuNC) with L-arginine. The enzyme substrate with strong PL intensity was formed through supramolecular host-guest assembly between guanidine group of L-arginine and AAT capped on the surface of AuNC. Upon arginase introduction, the captured L-arginine was hydrolyzed into ornithine and urea, thus resulting in the decreasing PL intensity. Based on this principle, a novel competitive-type immunoreaction was first carried out on AFB1-bovine serum albumin (AFB1-BSA) conjugate-coated microplate, using arginase-labeled anti-AFB1antibody as the competitor. Under the optimum conditions, the PL intensity increased with the increment of target AFB1, and allowed the detection of the analyte at concentrations as low as 3.2 pg mL-1(ppt). Moreover, L-arginine-AAT-AuNC-based PL enzyme immunoassay afforded good reproducibility and acceptable specificity. In addition, the accuracy of this methodology, referring to commercial AFB1ELISA kit, was evaluated to analyze naturally contaminated or spiked peanut samples, giving well-matched results between two methods, thus representing a useful scheme for practical application in quantitative monitoring of mycotoxins in foodstuff.

Concepts: Enzyme, Enzyme substrate, Product, ELISA, Immunoassay, Urea cycle, Ornithine, Magnetic immunoassay