# Radical-Mediated In Situ Fluorescence Dye Deposition: A Simple Interfacial Signal Amplification Reaction for Ultrasensitive Immunoassay on Barcode Beads

Article · Zhang J, Wang Y, Huang X, Wu H, Lin Q, Gu H, Jiang L, Zhu L, Xu H

- Archive id: doi:10.1002/advs.76670
- Published: 2026-07-20
- Venue: Advanced science (Weinheim, Baden-Wurttemberg, Germany)
- DOI: https://doi.org/10.1002/advs.76670
- PMID: 42474120
- PMCID: PMC13383694
- Citations: 0
- Source URL: https://doi.org/10.1002/advs.76670
- PDF: https://europepmc.org/articles/PMC13383694/pdf
- Provenance: europepmc

## Abstract

Ultrasensitive detection of low-abundance protein biomarkers is crucial for early disease diagnosis but remains challenging for the conventional barcode beads-based suspension chip platform due to the limited detection sensitivity. Here, we report a conceptually novel reaction termed "radical-mediated in situ fluorescence dye deposition" (RIFD) as a simple interfacial signal amplification strategy to overcome the limitation. This first discovered RIFD follows a universal "three-element principle", where the coexistence of beads, free radicals, and dyes suffices for fluorescence labeling, eliminating the pre-conjugation of dyes to detection probes required in traditional methods. Mechanistic studies reveal that this radical-triggered RIFD possibly follows three distinct pathways, including amide condensation on lysine residues, covalent biphenyl formation on tyrosine residues, or radical-dye co-deposition. It facilitates local and ultrafast (within 5 min) dye-trapping specifically on target-positive barcode beads. Consequently, the established RIFD-based immunoassay achieves a limit of detection of 12 fg/mL for IL-10, a 100-fold improvement over the conventional suspension chip method, and also successfully differentiates Alzheimer's disease patients from healthy controls by quantifying low-abundance plasma p-Tau217. Multiplexed detection is further validated with a three-plex cytokines panel. Our reported RIFD represents a powerful in situ fluorescence labeling tool, advancing protein biomarker detection toward the sub-pg/mL level with broad implications for clinical diagnostics.

_Abstract reproduced under CC-BY (article license as recorded by Europe PMC; abstract reproduced unmodified apart from markup removal)._

Topics: [Alzheimer's, Parkinson's & Neurodegeneration](https://space-kitty.com/topics/neurodegeneration)

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