Conceptual schematic of the microfluidic-based magnetic-field-driven manipulation of the liquid metal: (a) coating with Fe particles, (b) HCl treatment and suction of the liquid metal, (c) HCl-treated liquid metal injection into the PDMS-based microfluidic channel filled with HCl or NaOH, and (d) on-demand magnetic manipulation of the HCl-treated liquid metal.