Quantitative Detection of Molecular Oxygen in the Gas Phase with Fluorescent Nanodiamonds

ABSTRACT Quantitative detection of paramagnetic molecular oxygen (O 2 ) in gas mixtures was achieved via optically detected magnetic resonance (ODMR) of negatively charged nitrogen‐vacancy (NV − ) centers in fluorescent nanodiamonds. Diamonds approximately 70 nm in diameter were deposited in a microfluidic channel, and the oxygen concentration was varied from 0% to 100% (0 to 760 mmHg O 2 partial pressure) by mixing O 2 and N 2 gases at ambient pressure. ODMR contrast was measured using a double‐modulation lock‐in detection scheme applied to both optical and microwave excitations. ODMR contrast decreases linearly with oxygen partial pressure, with a sensitivity coefficient k of (‐10.1 × ± 0.3) × 10 −4 % mmHg −1 . The oxygen detection limit of the experimental setup was estimated to be approximately 8 mmHg O 2 partial pressure (corresponding to ca. 1% O 2 ). Cycling O 2 content in the gas mixture in the range of 0‐5 % revealed a hysteresis and corresponding repeatability of 0.006 in percent ODMR contrast. Fluorescence quenching and slow response (several to tens of minutes) upon oxygen concentration changes suggest physisorption of gas molecules on the nanodiamond surfaces contributes to equilibration dynamics. Transient bursts of molecular oxygen generated by enzyme‐catalyzed decomposition of hydrogen peroxide were also detected.