Fig. 2

Optofluidic particle trapping and its unperturbed steady-state dynamics. a Reproducible counterflow trapping (magenta) and free Brownian diffusion (green), illustrating the restoring effect of the thermoviscous trap and its role in limiting the spatial region sampled by the probe. b A histogram (heatmap) of the phase space explored by the trapped 3-\(\mu\)m particle in deionised water that indirectly shapes the outlines of the trap profile. c Similarly to optical tweezers, power spectral density analysis can be used to obtain a Lorentzian fit to the Fourier-transformed flow-trapping data and thus yield an accurate trap stiffness estimate along each transverse coordinate. The trap symmetry is evident from the agreement between the two in-plane stiffnesses, which overlap within the calculated uncertainties. The errors were calculated following a logarithmic binning procedure, where the magnitude of the standard deviation is inversely related to the number of data points comprising each bin