AFM Measurement of Self-Propulsion Forces Generated by A Janus Particle

Abstract

The behavior of Pt-coated Janus particle in aqueous hydrogen peroxide is studied using the atomic force microscopy (AFM) measurement. The catalytic chemical reaction between platinum and hydrogen peroxide generates the propulsion force to propel the Janus particle in the liquid. To characterize the self-propelling of Janus particle, a modified AFM probe with hanging Janus particle is newly designed and assembled. The self-propulsion force generated by Janus particle is then measured by recording and analyzing the force-versus-travel-distance curve and the power spectrum at an optimized immersion depth. Meanwhile, the theoretical origin of the propulsion force is thoroughly deducted. The propulsion peaks in power spectrum ranging from 100 to 300 Hz are analyzed to yield the concentration dependence of the propulsion peak location and height, the oscillation scale of the Janus particle, and the catalytic chemical reaction rate of Pt and hydrogen peroxide. Compared to the traditional method of optical tracking, the AFM measurement is faster and more accurate, and also suggests a new way of determining chemical reaction rate.