Electron Microscopy Provides Quantitative Insights into Modified Magnetic Bead Layers for Electrochemical Immunoassays

Abstract

Sensitive cytokine quantification is essential for understanding inflammatory disease mechanisms and guiding diagnostic development. Here, we characterize a magnetic bead electrochemical sandwich assay (MBESA) based upon 2.8 μm magnetic Dynabeads for the rapid electrochemical detection of the inflammatory cytokine interleukin-1β (IL-1β), a key mediator of immune signaling. Scanning transmission electron microscopy coupled with energy-dispersive X-ray spectroscopy (STEM-EDX) provided high-resolution visualization and quantitative mapping of conjugated MBESA layers. Incorporation of streptavidin-gold nanospheres provided direct, nanoscale evidence of antibody and antigen bioconjugation, revealing binding heterogeneity marked by a triplicate increase in sulfur content. This work demonstrates precise quantification of assay bioconjugation, addressing a critical gap in the structural characterization of bead-based immunoassays. By bridging biomolecule arrangement to assay performance, the MBESA positions itself as a leading electrochemical platform for inflammatory cytokine detection.