Response Characteristics and Mathematical Modeling for a Nitric Oxide Fiber-Optic Chemical Sensor

Abstract

A novel fiber-optic sensor for nitric oxide is constructed by holding a small amount of an internal reagent solution at the tip of a fiber-optic bundle with a piece of gas-permeable membrane. Nitric oxide diffuses across the membrane into this internal solution, where a chemiluminescent reaction between nitric oxide, hydrogen peroxide, and luminol takes place. The resulting light intensity is related to the concentration of nitric oxide in the sample. Results are presented from experiments to optimize the magnitude and rate of the sensor response. The resulting sensor possesses a limit of detection of 1.3 μM, a response time of 8-17 s, and a dynamic range from 5 to 40 μM. A mathematical model is derived to explain the sensor response as a function of time. Oxidation of nitric oxide by ambient oxygen and mass transport of nitric oxide through the gas-permeable membrane are considered in this model. The excellent agreement between experimental data and model predictions indicates that the oxidation of nitric oxide by oxygen is a major factor in this measurement, regardless of transducer element The model further indicates a reaction rate constant for the oxygen oxidation of nitric oxide of 9.5(±0.5) x 10 6 M -2 s -1 and a diffusion coefficient for nitric oxide in the silicone membrane of 5.0(±0.2) x 10 -11 m 2 s -1 at 30 °C.