Fabrication and characterization of a surface plasmon resonance based fiber optic urea sensor for biomedical applications

The fabrication and characterization of a surface plasmon resonance based fiber optic sensor for the detection of urea in liquid are reported. The probe is fabricated by coating three layers namely of silver, silicon and the enzyme, urease, over about 1 cm length of the unclad core of an optical fiber. The silicon layer protects silver from oxidation and enzyme from deactivation in addition to enhance the sensitivity of the sensor. The wavelength interrogation method is used to characterize the sensor. It is observed that the resonance wavelength decreases as the concentration of urea increases. The sensor operates in the urea concentration range of 0–160 mM, which is close to the physiological range of urea in blood and hence can be used in medical sciences. Further, the effects of concentration of urea on the sensitivity and detection accuracy of the sensor are studied. It is found that the sensitivity decreases with the increase in the concentration of urea whereas the detection accuracy is nearly independent of the urea concentration.