pH-Responsive Catalytic Janus Motors with Autonomous Navigation and Cargo-Release Functions

The fabrication of multifunctional polymeric Janus colloids that display catalytically driven propulsion, change their size in response to local variations in pH, and vary cargo release rate is demonstrated. Systematic investigation of the colloidal trajectories reveals that in acidic environments the propulsion velocity reduces dramatically due to colloid swelling. This leads to a chemotaxis-like accumulation for ensembles of these responsive particles in low-pH regions. In synergy with this chemically defined accumulation, the colloids also show an enhancement in the release rate of an encapsulated cargo molecule. Together, these effects result in a strategy to harness catalytic propulsion for combined autonomous transport and cargo release directed by a chemical stimulus, displaying a greater than 30 times local cargo-accumulation enhancement. Lactic acid can be used as the stimulus for this behavior, an acid produced by some tumors, suggesting possible eventual utility as a drug-delivery method. Applications for microfluidic transport are also discussed.