Extracted Active Fluctuations from an Active-Passive Mixture Reveal the Dynamic Class of Active Materials

Dynamic class of active materials, i.e., run-and-tumble, active Brownian, etc., can be characterized by the histograms of their active fluctuations. However, active fluctuations cannot be directly measured because they are always mixed with thermal fluctuations in experiments. Extracting the active fluctuations from that of a mixture is nontrivial because the histogram is not a linear superposition of the histograms of the active and passive fluctuations. We developed a deconvolution method to extract the active fluctuations from that of a mixture. Our deconvolution method is verified by Langevin-based numerical simulation of an active Brownian particle (ABP) in quadratic confinement. Using our method, we have extracted active fluctuations from an ICEP-driven particle in an optical trap, which reveals expected ABP dynamics. We have also extracted active fluctuations from a probe particle embedded in a suspension of E. coli, which reveals an unexpected run-and-tumble dynamic of the probe particle.