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<p>Protein-protein interactions govern the biomolecular logic of immunity, signalling, and disease. Elementary rates of association, dissociation, and inhibition underpin our understanding of life processes and remain a limiting factor at the frontier of therapeutic discovery. Yet existing assays infer these processes indirectly through ensemble-averaged signals or labels that obscure native dynamics. Here, we introduce a label-free, real-time, mass-resolved single-molecule immunoassay based on interferometric scattering microscopy (iSCAT) that directly observes individual protein-protein binding events in complex biological samples. By detecting light scattered from single proteins as they bind to an antibody-functionalized surface, we resolve discrete antibody-antigen interactions with single-molecule sensitivity and molecular-weight discrimination. Using IgM as a model system, we demonstrate real-time detection of individual binding events, with measured association rates that scale linearly with concentration over three orders of magnitude. Direct counts of IgM binding events in human serum yield quantitative concentrations that agree with bulk measurements obtained by enzyme-linked immunosorbent assay (ELISA). Spatially resolved tracking of individual binding and unbinding events captures the elementary dissociation rate constant, <InlineEquation ID="IEq1"><EquationSource Format="TEX">\(k_{\textrm{off}}\)</EquationSource></InlineEquation>, from the distribution of single-molecule dwell times. This bioaffinity iSCAT platform unifies molecular specificity, label-free detection, real-time kinetics, and mass-resolved single-molecule sensitivity, to offer a general framework for quantitative, single-molecule immunoassay.</p>

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Interferometric scattering microscopy supports real-time mass-resolved label-free single-molecule immunoassay

  • 期刊论文

  • 出版模式：

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  • 发表日期：

    2026年5月25日

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  • Carraugh C. Brouwer,
  • Flaminia M. Muratori,
  • Luke Melo,
  • Luigi Anastasia,
  • Carlo Pappone,
  • Edward Grant

摘要

Protein-protein interactions govern the biomolecular logic of immunity, signalling, and disease. Elementary rates of association, dissociation, and inhibition underpin our understanding of life processes and remain a limiting factor at the frontier of therapeutic discovery. Yet existing assays infer these processes indirectly through ensemble-averaged signals or labels that obscure native dynamics. Here, we introduce a label-free, real-time, mass-resolved single-molecule immunoassay based on interferometric scattering microscopy (iSCAT) that directly observes individual protein-protein binding events in complex biological samples. By detecting light scattered from single proteins as they bind to an antibody-functionalized surface, we resolve discrete antibody-antigen interactions with single-molecule sensitivity and molecular-weight discrimination. Using IgM as a model system, we demonstrate real-time detection of individual binding events, with measured association rates that scale linearly with concentration over three orders of magnitude. Direct counts of IgM binding events in human serum yield quantitative concentrations that agree with bulk measurements obtained by enzyme-linked immunosorbent assay (ELISA). Spatially resolved tracking of individual binding and unbinding events captures the elementary dissociation rate constant, \(k_{\textrm{off}}\), from the distribution of single-molecule dwell times. This bioaffinity iSCAT platform unifies molecular specificity, label-free detection, real-time kinetics, and mass-resolved single-molecule sensitivity, to offer a general framework for quantitative, single-molecule immunoassay.