An apparatus for perfusing an organ or tissue includes a perfusion circuit for perfusing the organ or tissue with a perfusate； and a sensor operatively connected to the perfusion circuit. The sensor includes a solid support to which is attached a recognition molecule that permits detection of the target agent. The recognition molecule specifically binds to the target agent in the presence of the target agent but not significantly to other agents. The sensor also includes an enzyme that can catalyze the conversion of a substance to glucose. In the presence of the target agent the enzyme can convert the substance into glucose, which can then be detected and optionally measured by the sensor.
