A target extraction system, comprising: (i) a flow cell, comprising: a chamber enclosing an interior and comprising a fluid inlet, a fluid outlet, and an inside surface facing the interior; and a plurality of surface-attached structures with a fixed end attached to the inside surface at a plurality of respective attachment sites and having an elongated geometry with a free end extending into the interior therefrom, each surface-attached structure comprising a flexible body and a metallic component disposed on or in the body, wherein the plurality of surface-attached structures are positioned in the fluid flow path established by the flow cell between the fluid inlet and fluid outlet of the chamber; and wherein the flow cell comprises a binding agent configured for binding to a target present in the interior, the binding agent selected from the group consisting of: a binding agent disposed on or integrated with an outer surface of at least some of the surface-attached structures; a binding agent disposed on or integrated with the inside surface; and both of the foregoing; the target extraction system being characterized by (ii) a driver configured for applying and rotating a magnetic or electric field to the interior of the flow cell to actuate gyratory movement of the surface-attached structures relative to the corresponding attachment site. (i) a flow cell, comprising: a chamber enclosing an interior and comprising a fluid inlet, a fluid outlet, and an inside surface facing the interior; and a plurality of surface-attached structures with a fixed end attached to the inside surface at a plurality of respective attachment sites and having an elongated geometry with a free end extending into the interior therefrom, each surface-attached structure comprising a flexible body and a metallic component disposed on or in the body, wherein the plurality of surface-attached structures are positioned in the fluid flow path established by the flow cell between the fluid inlet and fluid outlet of the chamber; and wherein the flow cell comprises a binding agent configured for binding to a target present in the interior, the binding agent selected from the group consisting of: a binding agent disposed on or integrated with an outer surface of at least some of the surface-attached structures; a binding agent disposed on or integrated with the inside surface; and both of the foregoing; the target extraction system being characterized by a chamber enclosing an interior and comprising a fluid inlet, a fluid outlet, and an inside surface facing the interior; and a plurality of surface-attached structures with a fixed end attached to the inside surface at a plurality of respective attachment sites and having an elongated geometry with a free end extending into the interior therefrom, each surface-attached structure comprising a flexible body and a metallic component disposed on or in the body, wherein the plurality of surface-attached structures are positioned in the fluid flow path established by the flow cell between the fluid inlet and fluid outlet of the chamber; and wherein the flow cell comprises a binding agent configured for binding to a target present in the interior, the binding agent selected from the group consisting of: a binding agent disposed on or integrated with an outer surface of at least some of the surface-attached structures; a binding agent disposed on or integrated with the inside surface; and both of the foregoing; the target extraction system being characterized by a binding agent disposed on or integrated with an outer surface of at least some of the surface-attached structures; a binding agent disposed on or integrated with the inside surface; and both of the foregoing; the target extraction system being characterized by (ii) a driver configured for applying and rotating a magnetic or electric field to the interior of the flow cell to actuate gyratory movement of the surface-attached structures relative to the corresponding attachment site.