Preparation and redox-controlled reversible response of ferrocene-modified poly(allylamine hydrochloride) microcapsules.

Single-component microcapsules were fabricated by the in situ reaction of ferrocenecarboxaldehyde (Fc-CHO) with poly(allylamine hydrochloride) (PAH) doped inside CaCO(3) microparticles, followed by core removal. The PAH-Fc microcapsules had very thick shells with remnant PAH-Fc inside, leading to a robust capsule structure that is less collapsed in the dry state. This single-component microcapsule is stabilized by the hydrophobic aggregation of Fc moieties and the protection of hydrophilic PAH backbones. Because of the excellent redox properties of Fc, the PAH-Fc microcapsules showed redox sensitivity to oxidation and reduction, as confirmed by UV-vis absorption spectroscopy and confocal laser scanning microscopy, resulting in reversible swelling and shrinking (11.7 vs 5.5 μm) in their size. Consequently, the permeability was also reversibly tuned, leading to the controlled loading and release of desired substances such as dextran.