Conformational Transduction Amplification in a Biomimetic Polyelectrolyte for Ultrasensitive Imaging of Iron...

Proteins exert sophisticated functions through stimulus-responsive conformational changes. Mimicking this structural control and functional integration in synthetic, water-soluble polymers has been a fundamental challenge, largely due to the conflict between charge repulsion and conformational order. Here, we report a peptidomimetic polyelectrolyte that overcomes this limitation, maintaining stable and well-defined helical and sheet-like conformations across the entire physiological pH range despite its high charge density. This intrinsic conformational order creates through-space conjugated carbonyl clusters that function as non-classical chromophores, enabling excitation-dependent near-infrared fluorescence with an exceptionally large Stokes shift. More importantly, the sheet-like conformation enables cooperative, multidentate chelation of Fe^{3 +} ions, which triggers an allosteric transition to a helix and results in nonlinear and ultrasensitive fluorescence quenching. Leveraging this unique "conformational transduction amplification" mechanism, we achieve real-time visualization and tracking of iron ion distribution and metabolic pathways at subcellular and whole-organism levels. This work establishes a paradigm of allosteric control in synthetic polyelectrolytes, opening avenues for the design of intelligent biomimetic materials for advanced sensing and imaging.