Elsevier

Talanta

Volume 233, 1 October 2021, 122407
Talanta

Magnetic field-enhanced agglutination as a readout for rapid serologic assays with human plasma

https://doi.org/10.1016/j.talanta.2021.122407Get rights and content

Highlights

  • Specific circulating antibodies could be detected in a homogenous format by the MFEA assay.

  • Results could be obtained from human plasma samples in 15 s only.

  • No matrix effect was detected despite a dilution rate of only five.

Abstract

Recent virus outbreaks have revealed a critical need for large scale serological assays. However, many available tests either require a cumbersome, costly apparatus or lack the availability of full automation. In order to address these limitations, we describe a homogeneous assay for antibody detection via measurement of superparamagnetic particles agglutination. Application of a magnetic field permits to overcome the limitations governed by Brownian translational diffusion in conventional assays and results in an important acceleration of the aggregation process as well as an improvement of the limit of detection. Furthermore, the use of protein-concentrated fluid such as 5 times-diluted human plasma does not impair the performances of the method. Screening of human plasma samples shows a strict discrimination between seropositive and seronegative samples in an assay duration as short as 14 s. The sensitivity of this method, combined with its quickness and simplicity, makes it a promising diagnostic tool.

Introduction

While immunoassays have been in use for several decades, they are still widely employed for detection and quantification of many biomarkers. Whereas enzyme-linked immunosorbent assay (ELISA) has represented the gold standard of immunoassays for many years [1], lateral flow tests are now largely employed, due to their easiness of use, their availability in settings outside the health care system as well as their short time-to-result. Recently developed quantitative lateral flow immunoassays are designed to detect a variety of biomarkers in several biological fluids, such as saliva, urine or whole blood [2], and limits of detection in the picomolar range may be reached in times between 10 and 30 min [3,4]. On the other hand, integration of such assays into high throughput, fully automated devices may be less easy than for ELISA tests. An ideal assay would thus combine the strengths of each format.

Many immunoassays now rely on the functionalization of colloidal particles [[5], [6], [7]] in order to increase surface/volume ratios, and to reduce diffusion times between analytes and their receptors, thus decreasing the duration of the assay as well as its limit of detection. Amongst those assays, it has been shown that, by applying a magnetic field to a suspension of superparamagnetic particles, they self-organize into linear chains, and the kinetics of agglutination of particles can be further increased, allowing the detection of proteins in the picomolar range in just a few minutes [8,9]. While original detection was simply realized by monitoring the extinction of light in the suspension, several alternate methods have since been developed to allow the detection of such aggregates. These methods may take advantage of the difference of diffusion coefficient between aggregated or non-aggregated particles [10], detect periodic variations of signal under a rotating field [[11], [12], [13]], or rely on a magnetic detection of aggregates [14,15]. One can observe that those assays are homogeneous assays, realized in only one step. This allows a reduced time-to-result as well as an improved easiness of use. On the other hand, interferences or cross reactions need to be addressed with special care, as they are generally reduced in heterogeneous assays thanks to washing steps.

In this communication, we present a homogeneous immunoassay based on magnetic field-enhanced agglutination (MFEA). Our objectives were to develop an assay with the sensitivity/specificity of an ELISA and a time-to-result as fast as that of a lateral flow immunoassay. As a proof-of-concept, we designed the study to detect anti-Zika virus antibodies. Indeed, while symptoms associated with Zika virus infection are generally similar to other arthropod-borne viruses [16,17], the Zika outbreak in the Americas has been associated with severe complications, such as neurological disorders or fetal malformations [[18], [19], [20]], therefore revealing a need for specific diagnostic tools. This assay was first set with purified antibodies, then assessed on human plasma samples. Performances of the assay such as signal-to-noise ratio, specificity and time-to-result have been compared to a commercial ELISA kit.

Section snippets

Materials and human samples

Human plasma samples were obtained from Etablissement Français du Sang, Montpellier, France. Monoclonal antibodies directed against Zika virus NS1 protein were provided by Alpha Diagnostic (ZNS112-M) and monoclonal antibodies raised against Dengue virus NS1 protein came from Abcam (Ab151179 and Ab138696).

The ELISA kit for detection of IgG antibodies to Zika NS1 was provided by InBios International (NuGen™ ZIKV IgG Capture ELISA Kit). Chemical products were all purchased from Sigma-Aldrich.

Magnetic particles functionalization

Results and discussion

To set up the assay, we first used MNPs coated with various quantities of Zika NS1 protein and commercial anti-Zika antibodies. The NS1 protein is targeted by about a third of the antibodies raised against the virus [24]. Aggregation could be observed on a typical OD recording in presence of 250 pmol.L−1 of a monoclonal antibody directed against the NS1 antibody (Fig. 2a).

While OD decreased during magnetization pulses due to the formation of linear chains of MNPs, OD increased sharply once the

Author information

All authors have given approval to the final version of the manuscript.

Credit author statement

Nevzat Temurok: conceptualization, investigation, methodology, validation, writing and editing. Fanny Leon: investigation, methodology, validation. Elena Pinchon: investigation, methodology, validation. Martine Clot: conceptualization, funding acquisition. Vincent Foulongne: conceptualization, methodology. Jean-François Cantaloube: conceptualization, methodology. Philippe Vande Perre: conceptualization, funding acquisition. Chantal Fournier-Wirth: conceptualization, methodology, supervision,

Declaration of competing interest

The authors declare the following financial interests/personal relationships which may be considered as potential competing interests: Nevzat Temurok, Martine Clot and Aurélien Daynès are company employees at HORIBA Medical.

Acknowledgment

This work has been financially supported by HORIBA Medical, Etablissement Français du Sang (EFS), University of Montpellier and Montpellier Université d'Excelence (MUSE) I-Site program (ArboMag project). We thank Françoise Maire at EFS Martinique and Guadeloupe for her helpful contribution towards this study. The authors wish to thank Morgana d’Ottavi for her careful reading of the manuscript.

References (26)

  • S. Schrittwieser et al.

    Homogeneous biosensing based on magnetic particle labels

    Sensors

    (2016)
  • Y. Ha et al.

    Recent advances incorporating superparamagnetic nanoparticles into immunoassays

    ACS Appl. Nano Mater.

    (2018)
  • J. Baudry et al.

    Acceleration of the recognition rate between grafted ligands and receptors with magnetic forces

    Proc. Natl. Acad. Sci. U.S.A.

    (2006)
  • Cited by (3)

    • Optomagnetic biosensors: Volumetric sensing based on magnetic actuation-induced optical modulations

      2022, Biosensors and Bioelectronics
      Citation Excerpt :

      Longer magnetic incubation time did not improve the assay performance due to the increased nonspecific bindings. Based on the short pulse magnetic incubation and turbidimetry, a compact optomagnetic setup (Fig. 2e) was built for one-step homogeneous assays of nucleic acids and antibodies, with clinically demonstrated practicability (Leon et al., 2021; Pinchon et al., 2020; Temurok et al., 2021). Integration of magnetic incubation system and sheath-less flow cytometry was reported for on-chip MFEA.

    1

    These authors contributed equally.

    View full text