Micro-environmental influences on artificial micromotors

The team's discoveries could help researchers to engineer micromotors which can traverse highly complex biological environments. These particles would prove invaluable for cutting-edge medical techniques including drug delivery and nano-surgery. In their study, Baraban and colleagues prepared two types of Janus sphere: the first one with a negatively charged surface, the second, with a positive charged coating. When placed in deionized water, both types generated an ion concentration gradient, and propelled themselves in opposite directions. Nearby, the researchers also placed a glass substrate carrying a variety of charge densities. When both substrate and particle coating had alike charges, the negative particles propelled themselves away from the surface at varying velocities.

For positively-charged substrates and particle coatings, Baraban's team found that these speeds showed a positive correlation with the substrate's charge density. According to the researchers, this behaviour arose since chemical reactions on the positively-charged coatings created their own ion concentration gradients in the surrounding fluid. This generated 'osmotic' flows along the charged substrate, causing the Janus particle to speed up. The discovery is a crucial step forward in our understanding of how self-propelled particles are influenced by the surrounding microenvironment. With further research, this could soon enable researchers to engineer Janus particles with specific speeds and directions, making them better suited to navigating complex environments.