A new optical sensing reaction for nitric oxide

Based on the reaction between the Cu(II) complex of Eriochrome cyanine R (ECR) and nitric oxide (NO) in phosphate buffer (pH 7.4), a new colorimetric method for the determination of NO concentration has been developed. The linear calibration range for NO was 0–60 μM with a detection limit of 1.24 μM. This reaction was then used as the basis in the development of a fibre optic chemical sensor for NO gas. The copper complex was incorporated into silicone rubber membranes and exposed to NO gas after incubating the films in phosphate buffer (pH 7.4). A linear calibration for NO gas between 0 and 6 ppm was obtained with a detection limit of 0.227 ppm (1 μM ≃ 0.031 ppm NO in solution). The sensor response was shown to be reproducible and reversible (2.77%, R.S.D., n=4) upon exposure to aqueous phosphate buffer (pH 7.4). The sensor response was also found to be pH independent between 7 and 10.