A wearable device includes a mount to mount the wearable device on a living body and a detector to detect an analyte response signal transmitted from tissue in the living body. The tissue contains a biologically active agent in an inactive state and functionalized particles. The biologically active agent can be converted to an active state that can affect a biological state of the living body. The functionalized particles are configured to bind with a target analyte, the presence or absence or concentration or abundance of which is correlated with the biological state. The analyte response signal is related to interaction of the target analyte with the functionalized particles. A source can apply directed energy into the tissue that is sufficient to convert the biologically active agent from the inactive state to the active state. A processor can determine a presence or absence or concentration or abundance of the analyte based on the analyte response signal.
