Surface plasmon resonance based fiber optic ethanol sensor using layers of silver/silicon/hydrogel entrapped with ADH/NAD

In this study an approach for the fabrication and characterization of a surface plasmon resonance (SPR) based fiber optic sensor for the detection of ethanol in 0–10 mM concentration range has been reported. The sensing probe has been prepared by coating films of silver and silicon over the unclad portion of an optical fiber followed by immobilization of enzyme (ADH) and coenzyme (NAD) entrapped hydrogel layer. The sensor works on spectral interrogation mode of operation. The resonance wavelength has been found to decrease with the increase in ethanol concentration. For the concentration range 0–10 mM, a 30 nm shift in resonance wavelength has been observed. The maximum sensitivity of the sensor has been found to be 21.70 nm/mM near zero concentration of ethanol solution. The calculated values of limit of detection (LOD) and limit of quantification (LOQ) of the sensor are 15.34 μM and 29.63 μM respectively. In addition, the sensor has high selectivity, repeatability and stability. Further, the sensor has various other advantages such as ease of operation, low cost, and fast response. Since the probe has been fabricated on optical fiber, it can work for online monitoring and remote sensing of analyte without any interference of electromagnetic fields.