A method for measuring or identifying a component of interest in a biological system is disclosed herein. The method includes positioning a fiber within the biological system, the fiber being at least partially coated with a polymeric extraction phase for adsorbing the component of interest from the biological system, the extraction phase being positioned within the biological system; adsorbing the component of interest onto the extraction phase; removing the fiber from the biological system; inserting the fiber into a nanospray needle; flowing solvent through the nanospray needle; desorbing the component of interest from the extraction phase into the solvent; and nanospraying the desorbed component of interest into an analytical instrument for measurement or identification.