(96h) Chemo and Phototactic Nano/Microbots

One of the most interesting scientific challenges is the design of synthetic motors on the nano and micrometer scales which could be used for drug delivery, self-assembly of superstructures, roving sensors, and other emerging applications. Our group was the first to report purely synthetic nano/micromotors. These autonomous motors consist of bimetallic segments which utilize hydrogen peroxide to power their movement through the solution. The mechanism of motion was determined to be self-electrophoresis, in which redox reactions catalyzed at the two metals create an electric field in solution which acts back on the rod.

We have achieved the attachment, transport, and delivery of a prototypical cargo, polymer microspheres, using bimetallic nanomotors. This may find application in bottom-up assembly of colloids or for delivery of materials at a specific location whereupon further binding events may be triggered depending on cargo surface functionality. Finally, an object that moves by generating a continuous surface force in a fluid can, in principle, be used to pump the fluid by the same catalytic mechanism. Thus, by immobilizing these bimetallic nanomotors, we have developed micro/nanofluidic pumps that transduce energy catalytically.

We have also explored an alternative mechanism to power synthetic micro/nanomotors, self-diffusiophoresis. In our case, each particle generates its own gradient of electrolyte that then acts back on the particle. We have shown that particles that release ions under UV illumination exhibit the phenomenon of phototaxis, the first examples outside living systems. Further, the gradients produced by adjacent particles interact and the particles began to swarm into concentrated groups. In this respect, the particles are reminiscent of quorum sensing organisms that swarm in response to a minimum threshold concentration of a signaling chemical.