Inline Mach–Zehnder interferometer with ZnO nanowires coating for the measurement of uric acid concentrations

• This paper is our original unpublished work describing the use of dumbbell shaped MZI coated with ZnO nanowires for detecting the various concentration of uric acid in distilled water.
• Various concentration of uric acid in distilled water is detected using a dumbbell shaped MZI coated with ZnO nanowires.

A simple optical fiber sensor is proposed and demonstrated using a dumbbell shaped inline Mach–Zehnder interferometer (MZI), which is coated with ZnO nanowires for measuring different concentrations of uric acid in de-ionized water. It is found that the interference spectrum of the sensor is red-shifted when the concentration of uric acid rises from 0 to 500 ppm. The peak-wavelength shift linearly increases with the increment in uric acid concentration. The sensitivity of the MZI sensor coated with ZnO is recorded at 0.001 nm/ppm with a good slope of linearity of more than 99% for a limit of detection (LOD) of 5.74%. On the other hand, the sensitivity of MZI-sensor without ZnO coating is 0.0005 nm/ppm with a slope of linearity of more than 99% and an LOD of 8.55%. It can be deduced that the sensitivity of the MZI-coated with ZnO is higher than the one without. This is due to the presence of the ZnO nanowires that trap water molecules within their mesh thereby improving the sensor’s response. These results show that the proposed sensor is applicable and useful for measuring the concentration of biochemical such as uric acid, glucose and fructose.