Abstract: Methods for making optical fiber sensor probes for measuring or monitoring parameters of fluids, including but not limited to measuring blood gas concentrations and pH either in a vessel in vitro or in a human artery. Such probes, in one aspect, have one or more optical fibers with one or more chambers with a chemical indicating materialtherein which changes in response to light transmitted therethrough. In one aspect such probes have a probe body including a plurality of fibers having a substantial portion of their surfaces covered with an opaque material to enhance light signal transmission therethrough. Such probes may also have a coating thereon of an anti-thrombogenic mnaterial.