Fibre Optic SPR Sensor Using Functionalized CNTs for the Detection of SMX: Comparison with Enzymatic Approach

Abstract

A novel approach for the detection of sulfamethaxazole (SMX) based on fibre optic surface plasmon resonance (SPR) technique and functionalized carbon nanotubes (CNTs) is proposed for 0 to 200 μM concentration range. The probe is prepared by immobilizing functionalized CNTs over silver coated unclad core of the fibre. The sensor’s performance is compared with a fibre optic enzyme-based SPR sensor. In the enzyme-based sensor, layer of functionalized CNTs is replaced by the layer of tyrosinase enzyme embedded polyacrylamide gel. It is found that the resonance wavelength in case of enzyme-based probe and the peak absorbance wavelength in the case of CNT-based probe show a red shift as the concentration of SMX is increased. Both the probes are characterized and optimized in terms of sensitivity, limit of detection, selectivity, pH and repeatability. The maximum sensitivities for enzyme and CNT-based sensors are found to be 0.29 and 0.37 nm/μM, respectively. Further, the corresponding limits of detection (LODs) are 1.137 and 0.8918 μM, respectively. The values of LOD are compared with the values reported in the literature for SMX sensors based on other methods/techniques. The proposed sensor utilizing CNTs is found to be the best in terms of LOD. The other advantages of proposed sensor are low cost, high sensitivity and better selectivity in addition to the advantages of remote sensing, real time monitoring, miniaturized probe and ease of handling which are due to the use of optical fibre as substrate for probe fabrication.