Superassembled Biocatalytic Porous Framework Micromotors with Reversible and Sensitive pH-Speed Regulation at Ultralow Physiological H2O2 Concentration

Synthetic nano/micromotors are a burgeoning class of materials with vast promise for applications ranging from environmental remediation to nanomedicine. The motility of these motors is generally controlled by the concentration of accessible fuel, and therefore, engineering speed-regulation mechanisms, particularly using biological triggers, remains a continuing challenge. Here, control over the movement of superassembled porous framework micromotors via a reversible, biological-relevant pH-responsive regulatory mechanism is demonstrated. Succinylated -lactoglobulin and catalase are superassembled in porous framework particles, where the -lactoglobulin is permeable at neutral pH. This permeability allows the fuel (H2O2) to access catalase, leading to autonomous movement of the micromotors. However, at mild acidic pH, succinylated -lactoglobulin undergoes a reversible gelation process, preventing the access of fuel into the micromotors where the catalase resides. To one's knowledge, this study represents the first example of chemically driven motors with rapid, reversible pH-responsive motility. Furthermore, the porous framework significantly enhances the biocatalytic activity of catalase, allowing ultralow H2O2 concentrations to be exploited at physiological conditions. It is envisioned that the simultaneous exploitation of pH and chemical potential of such nanosystems could have potential applications as stimulus-responsive drug delivery vehicles that benefit from the complex biological environment.