Behavior of ligand binding assays with crowded surfaces: Molecular model of antigen capture by antibody-conjugated nanoparticles

Abstract

Ligand-receptor binding is of utmost importance in several biologically related disciplines. Ligand binding assays (LBA) use the high specificity and high affinity of ligands to detect, target or measure a specific receptors. One particular example of ligand binding assays are Antibody conjugated Nanoparticles (AcNPs), edge-cutting technologies that are present in several novel biomedical approaches for imaging, detection and treatment of diseases. However, the nano-confinement in AcNPs and LBA nanostructures introduces extra complexity in the analysis of ligand-receptor equilibriums. Because antibodies are large voluminous ligands, the effective affinity in AcNPs is often determined by antibody orientation and surface coverage. Moreover, antibodies have two binding sites introducing an extra ligand-receptor binding equilibrium. As consequence of all this, experimental or theoretical studies providing a guidelines for the prediction of the binding behavior in AcNPs are scarce. In this work, we present a set of theoretical calculations to shed light into the complex binding behavior of AcNPs and its implications in biomedical applications. To investigate the ligand-receptor binding on AcNPs, we have used a molecular theory that predicts the probability of different molecular conformations of the system depending on the local environment. We have considered two different pathways for designing these devices: covalently conjugated antibodies and streptavidin-biotin conjugated antibodies. We also explore the effects of surface coverage, bulk concentrations, nanoparticle size and antibody-antigen affinity. Overall, this work offers a series of theoretical predictions that can be used as a guide in the design of antibody conjugated nanoparticles for different applications.

Ligand‐Installed Nanocarriers toward Precision Therapy

“…The affinity ability between the ligands and receptors can be reflected by their equilibrium binding constant K or disassociation constant K D (i.e., 1/ K ) . For instance, the K D of antigens and antibodies in the range of 10 −8 to 10 −11 m is generally regarded as high affinity . K and K D can be simulated, as well as measured with a molecule model of ligand‐installed nanocarriers and receptors by surface plasmon resonance (SPR) .…”

“…[70] For instance, the K D of antigens and antibodies in the range of 10 −8 to 10 −11 m is generally regarded as high affinity. [71] K and K D can be simulated, [72] as well as measured with a molecule model of ligandinstalled nanocarriers and receptors by surface plasmon resonance (SPR). [73] For instance, the K D of folic acid-installed dendrimer nanocarriers with average of 2.6 to 13.7 folic acids has been evaluated, demonstrating values of K D from (2 ± 1) × 10 −9 to (7 ± 6) × 10 −11 m. [74] Interestingly, the K D increased from (2 ± 1) × 10 −9 to (7 ± 6) × 10 −11 m by increasing folic acid from 2.6 to 4.7, but then decreased from (7 ± 2) × 10 −11 to (3 ± 2) × 10 −11 m when the folic acid was increased from 7.2 to 13.7, demonstrating that the ligand density could affect the targeting ability of the ligand-installed nanocarriers.…”

Direct immunoassays and their performance – theoretical modelling of the effects of antibody orientation and associated kinetics

“…Some studies, [1,2], report that extremely small (typically less that 10%) fractions of antibodies are still capable of binding antigen after immobilization. In addition, the functionality of immobilized antibodies is of great importance to other biomedical applications (such as artificial tissues and implants or targeted drug delivery systems) as well as immune reactions in vivo [3].…”

“…The amount of captured antigen has been studied as a function of antibody surface coverage both theoretically and experimentally by several authors [1,2,4,3]. However, since the density of adsorbed antibodies is known to affect their orientation, accessibility and binding ability, it is often not clear which of these properties has a greater impact on the assay signal, and their separate assessment can be difficult to achieve in practice [5].…”

Specific Decoration of a Discrete Bismuth Oxido Cluster by Selected Peptides towards the Design of Metal Tags

“…[8] As there is only one detectable lanthanidep er taggingu nit in these mononucleartags, they are usually limited in their ultimate sensitivity,w hicht riggered investigations on polymerbased tags [9] and nanoparticles. [10] Yet, ap recise quantification of biomolecules was not realized due to the broad size distributiono ft hese systems. [11] An obviousa dvancement wouldb e the employment of clearly defined clusters:t he design of water soluble, multi-nuclear metal tags would increase the overall analytical performance, and investigations with molecular chemistry methods would be possible.…”