Disclosed herein is a two-piece sensor assembly that includes an attachment collar configured to attach to a body surface of a patient and comprising at least one opening, and a skin sensor configured to seat into the at least one opening in the attachment collar. The skin sensor includes at least one radiation source configured to irradiate the body surface with at least one interrogation light, and at least one detector configured to detect at least one response light incident from the direction of the body surface.
