Optical Fiber Probe for the Selective Plasmonic Sensing of Catechol Utilizing ZnO Decorated MWCNTs

The widespread use of dihydroxybenzenes in various industries like photography, pesticides, dyes, antioxidants and medicines has lead their inadvertent disposal in soil and water. Catechol is an isomer of dihydroxybenzene whose disposal in ground and river water has necessitated requirement of its highly sensitive sensor due to its toxic effects. Being of polar nature it is easily uptaken by cells but not released properly leading to its accumulation in cells. It is regarded as human group 2B carcinogen by IARC with severe effect on central nervous system. Due to its toxicity, co-carcinogenic activity and low biodegradability it is declared as serious threat for ecology by USEPA and Europian Union [1, 2]. Therefore, we report, here, a selective and sensitive surface plasmon resonance (SPR) based catechol sensor utilising zinc oxide decorated multi-walled carbon nanotubes (MWCNTs) functionalised with CTAB (cetyl trimethyl ammonium bromide) as a sensing layer on an optical fiber probe. Surface plasmon technique makes the sensor highly sensitive, whereas use of an optical fiber provides the advantage of miniaturised probe with facility of continuous online monitoring. The sensor fabrication broadly consists of three steps. The first step involves the chemical route for the preparation of nanocomposite. Firstly, ZnO nanoparticles were prepared through the reduction of zinc acetate by NaOH. Then the nanoparticles were decorated on sidewall functionalised MWCNTs followed by functionalization with CTAB [3]. The TEM image of ZnO decorated MWCNTs is shown in fig.1(a). The second step involves the thermal deposition of silver on 1 cm uncladded region of the fiber probe. Finally, the nanocomposite was coated on the fiber probe by dip coating method. All the steps of probe fabrication are schematically depicted in fig.1(b). To characterize, the probe was fixed in a flow cell having the facility of inlet and outlet for the samples. Polychromatic light was launched from one end of the probe and the SPR spectrum of the catechol sample of a given concentration in the flow cell was recorded by the spectrometer at the other end.