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

Abstract

When ligands and receptors are both attached on surfaces, because of the restriction of configurational freedom, their recognition kinetics may be substantially reduced as compared with freely diffusing species. In nature, this reduction may influence the efficiency of the capture and adhesion of circulating cells. Here we show that similar consequences are observed for colloids grafted with biomolecules that are used as probes for diagnostics. We exploit Brownian magnetic colloids that self-assemble into linear chains to show also that the resulting one-dimensional confinement considerably accelerates the recognition rate between grafted receptors and their ligands. We propose that because confinement significantly augments the colliding frequency, it also causes a large increase in the attempt frequency of the recognition. This work gives the basis of a rapid, homogeneous, and highly sensitive bioanalysis method.association rate ͉ bioassay ͉ magnetic colloids ͉ specific adhesion D iagnostics techniques are generally based on building a specific immunocomplex structure in which the antigen to be detected is recognized by two antibodies (1-8). Early immunochemistry was based on precipitation of large complexes made of antibodies and antigens. Following the same track, the use of Brownian particles significantly improved the detection sensitivity, because of the increase in scattered light when aggregation between grafted colloids takes place. As the most simple but very generic example, let us consider an antigen Ag having two different epitopes for two antibodies, A and B. To reveal the presence of such antigen, particles grafted with A and B antibodies are mixed with the sample to be analyzed. The formation of small clusters is then expected, at a rate depending on many factors. Change in light scattering due to the presence of these small clusters will reveal the existence of sandwich-like structures: A-Ag-B (latex agglutination immunoassay). These homogeneous assays, as opposed to heterogeneous assays in which washing steps are necessary before detection, are today by far the most simple and straightforward assays. They were introduced Ͼ40 years ago (2), and today several hundred different tests based on this principle can be found on the market, mainly for infectious disease detection and protein quantification, as long as the antigen concentration to be detected is տ1 nmol͞liter (1). Meanwhile, many diagnostic assays require sensitivity in the picomolar range. They are presently performed by using a heterogeneous approach (such as ELISA) (1). For that range of concentration, if we were still to consider the same homogeneous approach, it would in principle take too long. Indeed, decreasing the number of antigens to be detected implies also decreasing the number of particles in solution, † and thus the particles' colliding frequency. Therefore, at these very low antigen concentrations, the encounter frequency between species becomes a critical issue to consider.In this work, we demonstrate conditions that ac...

Assembly of vorticity-aligned hard-sphere colloidal strings in a simple shear flow

“…and therefore, accelerate rates at which particles form contactsa method potentially useful for rapid bioanalysis if biofunctionalized particles are used (35)(36)(37).…”

Resistive pulse sensing of magnetic beads and supraparticle structures using tunable pores

“…56 For applications in which target analytes contain multiple binding sites or epitopes, it is possible for the target to bind to multiple beads simultaneously, leading to aggregation. 41,[57][58][59] Multiple-particle binding has been used in LM, allowing detection of the dengue virus at 10 plaque forming units ml À1 . 41 Alternative methods monitor aggregation using chain length, 60 turbidity, 57 or changes in magnetic properties when particles are in close proximity to each other.…”

“…41,[57][58][59] Multiple-particle binding has been used in LM, allowing detection of the dengue virus at 10 plaque forming units ml À1 . 41 Alternative methods monitor aggregation using chain length, 60 turbidity, 57 or changes in magnetic properties when particles are in close proximity to each other. 58 The fundamental reason for the high utility of SPMs is that the physics of bead manipulation is independent of usual microfluidic and biological processes.…”

Blu-ray based optomagnetic aptasensor for detection of small molecules

“…Accordingly, the addition of a target triggers clustering of MNPs, leading to changes in the size and the number of agglomerated particles with the analyte concentration, which is referred to as a clustering assay (Aurich et al 2006;Baudry et al 2006;Castañeda et al 2007;Göransson et al 2010;Josephson et al 2001;Koh et al 2009;Liang et al 2011;Ling et al 2010;Perez et al 2002;Ranzoni et al 2012;Zhang et al 2013a). Such a volume-based MNP clustering assay is particularly appealing since it allows simple mix-and-read type measurements and reduced reaction time by use of external magnetic fields (Baudry et al 2006). Despite these advantages, the extensive use of MNP clustering assays has been impeded by the following limitations: First, the typical clustering assay is applicable only to a target molecule with multiple binding sites, but not feasible for small molecules due to their limited number of binding sites.…”