Phenol Sensing Based on Plasmonic Refractive Index Optical Sensor Incorporated Sodium Carboxymethyl Cellulose

The industrial sectors have experienced substantial growth to meet the demands of human society. However, this expansion has come at a cost to living organisms, including humans, due to the extensive discharge of phenol, an essential raw material in these sectors, into aquatic environments as a by-product. This has subsequently prompted the development of various techniques for phenol detection. Nonetheless, certain techniques have encountered flaws, such as being costly and challenging to execute. Consequently, surface plasmon resonance (SPR) has emerged as a valuable optical sensor to address the limitations of previous methods. In this study, this plasmonic refractive index sensor has been incorporated with sodium carboxymethyl cellulose (NaCMC) for phenol sensing. The performance of the sensor was evaluated over a wide range of phenol concentrations from 0.01 to 100 fM. Increased phenol concentrations led to a notable rightward shift in the SPR curves. It also demonstrated a commendable sensitivity value of 0.00895°/M (R2 = 0.99) with the lowest detectable concentration of 0.01 fM. Additionally, the optical properties of the sensor film and phenol were determined by fitting the experimental SPR curves to theoretical data. It was revealed that the values of the real and imaginary parts of the refractive index for all phenol concentrations were the same as those for deionized water. On the other hand, the real part of the refractive index and the thickness of the NaCMC layer increased with rising phenol concentrations, while the imaginary part of the refractive index decreased. Besides, atomic force microscopy analysis confirmed the variations in sensor surface roughness and structure, validating the adsorption of phenol on the sensing layer. This NaCMC-based SPR sensor demonstrates superior sensing performance when compared to the previously developed optical sensors, establishing it as a promising technology for applications in environmental monitoring.