Abstract

Phenolic compounds are notable for its noxious effects on human beings, animals as well as on plants. These compounds can be seen commonly in sewage water and industrial byproducts and release toxic products while decomposing, especially in a fire. Thus different phenolic compounds such as catechol, phenol, m-cresol, 4-chlorophenol, p-cresol, o-cresol have been reported in large quantities in the environment which creates potential hazard to life mainly from oral exposure. Of these, para-cresol (p-cresol) also known as 4-methyl phenol is an organic compound, that comes in the phenolic family, which has reported its adverse effects especially for human life [1]. It has been used as an intermediate product in industries for producing chemicals, antioxidants, as disinfectants, adhesives, corrosion inhibitors, preservatives in cleaning agents etc. The LD50 values of the phenolic compounds are in the range of 200 to 2050 mg/kg/day in several species in acute oral toxicity studies. Drastic exposure of cresol can affect nervous system, brain functioning and respiratory failure which may lead to death. There are various standard methods in use around the world for monitoring the level of these unsafe compounds such as amperometric detection, spectrophotometry, liquid chromatography etc. All these methods have some disadvantages like time consumption, low sensitivity, demand of expert to monitor it, electrode fouling, high cost etc [1,2]. Here, an optical method has been used with optical fiber employing the technique of surface plasmon resonance (SPR), which has numerous advantages such as online monitoring, low cost, remote sensing, real time detection, better sensitivity and limit of detection [2]. Surface plasmons are excited by the evanescent field generated by a TM wave at the metal dielectic interface by satisfying the TIR condition. The maximum transfer of light energy occurs at the resonance wavelength for spectral interrogation method in optical fiber based systems. A change in the dielectric nature of the sensing layer results in a shift in the resonance wavelength. Measuring the change in resonance wavelength and dip in the SPR curve gives a measurement of the change in the sensing layer refractive index [2]. In the present paper, an exploratory work has been reported for para-cresol sensing using optical fiber and SPR. The enzyme that has been reported for phenolic compound sensing is tyrosinase [1]. The sensor has been designed by using zinc oxide (ZnO) nanoparticles which acts a matrix for direct physical adsorption. Zinc oxide nanoparticle has been used that has a high IEP of 9.5, thus facilitating direct physical adsorption of the enzyme having low IEP. A natural polymer chitosin is also used with ZnO to enhance its adhesive property [1]. The proposed sensor operates in the range of 0 µM to 1000 µM of p-cresol.

© 2015 Japan Society of Applied Physics, Optical Society of America