In the past years, there has been a thriving enthusiasm on seeking efficient enzyme-powered micromotors1 for their encouraging biomedical applications promoted by self-propulsion, for instance targeted delivery,2 sensing, surgery, and detoxification.3
However, a better understanding of the fundamental aspects of enzyme-powered self-propulsion is required before any feasible implementation. Enzymatic reactions are divided in two steps: the binding-unbinding processes of an uncatalyzed substrate and its catalysis into a product. The approach of this project addresses the question of which is the role of each step for the self-propulsion of micromotors.
First, to determine the importance of catalysis, multiple enzymes are selected based on their different turnover numbers (kcat, catalytic rate per active site): urease, acetylcholinesterase, glucose oxidase and aldolase. These enzymes are attached to Hollow Silica Microparticles (HSMP) and a detailed characterization is performed prior to motion analysis. After comparing their motion dynamics, a clear correlation between the velocity of the micromotor and the kcat of its enzyme is observed. This points the catalysis as a crucial step for self-propulsion generation of microstructures.
On the other hand, to study the binding-unbinding processes and determine if they are enough by themselves to produce self-propulsion, the urease micromotors are exposed to different concentrations of acetohydroxamic acid -a competitive reversible inhibitor- which interacts with the active site but is never catalyzed. No self-propulsion is observed, but to detect any minor contribution of these processes even with catalysis taking place, the urease micromotors are exposed again to different concentrations of acetohydroxamic acid but with urea present in excess. This allows to establish a positive correlation between the velocity of the micromotors and their enzymatic activity, confirming catalysis as the pivotal step of the reaction without any detectable contribution of the binding-unbinding processes.
- Ma, X.; Hortelao, A.C.; Patiño, T.; Sánchez, S. Enzyme catalysis to power micro/nanomachines. ACS Nano 2016, 10, 9111–9122.
- Hortelão, A.C.; Patiño, T.; Pérez-Jimenez, A.; Blanco, A.; Sánchez, S. Enzyme-powered nanobots enhance anticancer drug delivery. Adv. Funct. Mat. 2017, 1705086.
- Li, J.; Esteban-Fernández de Ávila, B.; Gao, W.; Zhang, L.; Wang, J. Micro/nanorobots for biomedicine: Delivery, surgery, sensing, and detoxification. Sci. Robot. 2017, 2, eaam6431.