Capsules as Miniature Factories: On-Demand Synthesis in Prepackaged Capsules Enabled by Switching on a Catalytic Reaction

Biological cells convert reactants into products using enzymatic catalysis-moreover, such synthesis is done as needed. This paper presents a platform of polymer capsules that emulate the ability to synthesize products on-demand (i.e., these miniature factories remain dormant at the outset, but can be switched on when needed). The structures created are multicompartment capsules (MCCs) having one or more internal compartments. Hydrophilic solutes are hermetically sealed in the compartments by constructing a hydrophobic wax shell around the aqueous core. While such a shell is initially impermeable, solute transport can be activated by a thermal switch, i.e., by melting the shell. The MCC factory is used to synthesize fluorescent nanoclusters (NCs) of gold and cadmium, which are useful as sensors and in bioimaging. The reaction is triggered by releasing a base from its compartment, whereupon a protein in the MCC lumen catalyzes the NC synthesis. In another example, a chemical fuel (H2O2) is released into the MCC lumen, where catalytic silver particles decompose the fuel to generate oxygen gas. The gas induces the MCC to inflate and eventually rupture-the MCC thus exhibits an emergent autonomous response that is the property of the whole, but not of any component parts.

Automated summary

This paper presents a platform of polymer capsules that can synthesize products on-demand. The capsules are multicompartment structures that can transport solutes and trigger reactions using a thermal switch. The platform was used to synthesize fluorescent nanoclusters and demonstrate the autonomous response of the capsules.