Responsive microcapsule reactors based on hydrogen-bonded tannic acid layer-by-layer assemblies

We explore responsive properties of hollow multilayer shells of tannic acid assembled with a range of neutral polymers, poly( N -vinylpyrrolidone) (PVPON), poly( N -vinylcaprolactam) (PVCL) or poly( N -isopropylacrylamide) (PNIPAM). We found that properties of the nanoscale shells fabricated through hydrogen-bonded layer-by-layer (LbL) assembly can be tuned changing the interaction strength of a neutral polymer with tannic acid, and by a change in counterpart hydrophobicity. Unlike most hydrogen-bonded LbL films with two polymer components, the produced tannic acid-based multilayer shells are extremely stable in the wide pH range from 2 to 10. We demonstrate that gold nanoparticles can be grown within tannic acid-containing shell walls under mild environmental conditions paving the way for further modification of the capsule walls through thiol-based surface chemistry. Moreover, these shells show reversible pH-triggered changes in surface charge and permeability towards FITC-labeled polysaccharide molecules. The permeability of these LbL containers can be controlled by changing pH providing an opportunity for loading and release of a functional cargo under mild conditions. Tannic acid-based assemblies show pH-switchable surface charge/permeability. They can produce gold nanoparticles allowing further film modification and can be potentially useful as responsive coatings for biochemical sensing or biotechnology applications.