We report on a reflection-mode fiber-optic oxygen sensor based on the O42 quenching of the red emission from hexanuclear molybdenum chloride clusters. Measurements of the probe operating in a 0%–21% gaseous oxygen environment have been obtained, a range suitable for biological and automotive applications. The luminescence signal increases with decreasing oxygen concentration in accordance with theory. We observe clearly resolvable steps in the sensor response for changes of 0.1% absolute oxygen concentration in the 0%–1.0% range. The response time of the fiber probe is theoretically predicted to be 1 s.

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The charge of the electron can be determined by simply placing a known number of electrons on one electrode of a capacitor and measuring the voltage, Vs, across the capacitor. If Vs is measured in terms of the Josephson volt and the capacitor is measured in SI units then the fine-structure constant is the quantity determined. Recent developments involving single electron tunneling, SET, have shown bow to count the electrons as well as how to make an electrometer with sufficient sensitivity to measure the charge.

We report on an optical oxygen sensor for aqueous media. The phosphorescent signal from the indicator, K 2 Mo 6 Cl 14 , immobilized in a polymer matrix, is quenched by ground state 3 O 2. Continuous measurements ͑⌬t=10 s͒ over 36 h in oxygen atmospheres ͑0%-21%͒ were obtained with a signal to noise ratio better than 150. Photobleaching was not observed over ϳ13 000 measurements. The senor response at 10, 22, and 37°C water is governed by bimolecular collisional quenching, as evidenced by a linear fit to the Stern-Volmer equation for dissolved oxygen in the range 0 Ͻ ͓O 2 ͔ Ͻ 3 ϫ 10 −4 .

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