Ultra-Sensitive, Selective, and Humidity Resistant Detection of Nitric Oxide

Case ID:

This invention is a Whispering-Gallery Mode (WGM) microtoroidal optical resonator designed for ultra-sensitive detection of nitric oxide gas, achieving remarkable precision with a detection limit as low as 2.34 parts per trillion (ppt). This exceptional sensitivity is achieved through the utilization of ferrocene-containing polymeric coatings created via RAFT polymerization, which enhance selectivity for the target analyte, nitric oxide. The system, known as the Frequency Locked Optical Whispering Evanescent Resonator (FLOWER), tracks the real-time shifts in resonance with sub-femtometer resolution as nitric oxide gas is introduced, allowing for both reversible and irreversible sensing within a concentration range of 6.4 ppt to 240 ppt and even higher concentrations. Notably, the device also exhibits robust resistance to humidity, maintaining its sensing performance effectively up to 47% humidity. The study evaluates the impact of different chemical compositions and molecular weights of the ferrocene-containing polymeric coatings on sensing performance. This invention represents a significant advancement in gas sensing technology, enabling the detection of extremely low concentrations of nitric oxide with high precision and selectivity.

Systems for the selective and rapid detection of gases are important tools used to monitor environmental impacts, occupational safety, and human biomarkers. Nitric oxide is a common byproduct of vehicle exhaust and industrial processes involving combustion, making it a major emission contributing to ozone layer depletion. In addition to its environmental impacts, nitric oxide also serves as an important biomarker of respiratory health associated with asthma and Chronic Obstructive Pulmonary Disease (COPD). Furthermore, nitric oxide is easily oxidized in air to nitrogen dioxide, which is highly corrosive, toxic, and a danger to human respiratory health. To mitigate injury due to gas exposure and monitor the environmental impacts of industrial processes, selective sensors for nitric oxide detection must be developed and deployed.

Current solutions for nitric oxide detection typically rely on various methods, including chemiluminescence, electrochemical sensors, and optical sensors such as cavity ring-down spectroscopy. However, these methods often struggle to achieve the level of sensitivity and selectivity needed for accurately measuring trace concentrations of nitric oxide in complex environments. This technology is capable of real-time, reversible and irreversible sensing over a wide concentration range while maintaining resistance to humidity, making it a versatile and highly effective tool for nitric oxide detection, surpassing the limitations of traditional detection methods.


  • Nitric oxide detection
  • Industrial safety
  • Occupational safety
  • Environmental impact and research
  • Biomedical research


  • Increased sensitivity 
  • Wide detection range
  • Resistant to humidity
Patent Information:
Contact For More Information:
Richard Weite
Senior Licensing Manager, College of Optical Sciences
The University of Arizona
Lead Inventor(s):
Tsu-Te Su
Yinchao Xu
Allison Stanko
Chloe Cerione
Trevor Lohrey
Euan Mcleod
Brian Stoltz