A fiber-optic (FO) element-based sensing probe for use in monitoring parameters of a biological environment. A straight FO-element, embedded and cast in a polymeric body of the probe delivers excitation light from a light source on one side of the FO-element to a chamber, inside the body, that is filled with an indicator matrix responsive to the excitation light and to the presence of a biological environment. The same straight FO-element collects light from the chamber and delivers it, in an opposite direction, from the chamber to an optical detector. The chamber may be configured to be co-axial with the FO-element and to have a transverse dimension, across the axis of the FO-element, exceeding the outer diameter of the core of the FO-element. A membrane permeable to an analyte of the biological environment is disposed in a recess of the chamber adjoining the aperture defined by the chamber in an outer side surface of the polymeric body.