A wearable device includes a mount configured to mount the wearable device to an external body surface proximate to a vessel, a downstream clamp configured to apply a force to the vessel sufficient to inhibit a flow of fluid through the vessel beyond the downstream clamp, and an upstream clamp, positioned upstream of the downstream clamp, configured to apply a force to the vessel sufficient to accelerate a volume of fluid in a downstream direction with respect to a direction of fluid flow through the vessel. A detector may also be provided for detecting a response signal transmitted from a probe region of the vessel positioned upstream of the first clamp. The response signal is related to the presence or absence of one or more target analytes in the vessel.
