Nitric oxide (NO) sensors are of great interest because of the role NO plays in regulating chemical and biological processes, including vasodilation, neurotransmission and immune response. Research reported in Applied Physics Letters describes a new optogalvanic gas sensor for NO based on Rydberg excitations that could be an improvement over existing detection methods.

Based on results from a proof-of-concept study, a sensor prototype detected NO concentrations lower than 10 parts per million in gas volumes as small as 10−4 liters. The sensor is operated at room temperature and can be used at normal atmospheric pressures — improving on current NO detection methods that require liter-scale gas volumes and can suffer from cross-sensitivities to similarly sized molecules and changes in temperature or pressure.

The sensor prototype consists of a glass chamber containing NO and helium gas, two metal electrodes, a high-bandwidth and temperature-compensated transimpedance amplifier (TIA), and two Nd:YAG-pumped dye lasers specifically tuned to form a Rydberg gas of NO. Laser pulses entering the glass chamber create Rydberg-excited NO molecules. The electron of a Rydberg-excited NO molecule is only weakly bound, so that any low-energy collision that happens to it in the chamber can lead to ionization. This ionization is picked up by the electrodes as an electrical charge that is amplified and converted into a voltage reading by the TIA. Since only the NO molecules in the gas mixture are Rydberg-excited, any electrical charge picked up by the sensor’s electrodes is an indication of the presence of NO.

While the sensitivity of the new sensor does not exceed other NO gas sensors, the proof-of-concept results show promise for the proposed Rydberg detection scheme.

Source: “Proof of concept for an optogalvanic gas sensor for NO based on Rydberg excitations,” by J. Schmidt, M. Fielder, R. Albrecht, D. Djekic, P. Schalberger, H. Baur, R. Löw, N. Fruehauf, T. Pfau, J. Anders, E. R. Grant, and H. Kübler, Applied Physics Letters (2018). The article can be accessed at