Graphene oxide coated U-bent plastic optical fiber based chemical sensor for organic solvents

Abstract

This study describes the development of a refractive index (RI) based fiber optic chemical sensor using a U-bent plastic optical fiber (BPOF) probe made of 0.5 mm polymethylmethacrylate (PMMA) core and optimum bend diameter of 1.4 mm coated with graphene oxide (GO) film. GO film on BPOF sensor surface significantly enhance the RI sensitivity of the sensor as well as its chemical resistance due to improved refractive index contrast and (PMMA) surface passivation by GO respectively. GO was chemisorbed to hexamethylenediamine (HMDA) functionalized BPOF probe surface by identifying the optimum GO concentration (100 μg/ml) and incubation time (24 h). An enhanced RI sensitivity of 9.42 ± 0.37 (ΔA845nm/ΔRIU) was achieved using GO coating of thickness 3.3 μm, which is 3.6 times higher than that of the bare BPOF probe. The RI sensitivities in presence of organic solvents including methanol, ethanol and isopropyl alcohol are found to be 12.75 ± 1.19, 9.97 ± 0.66 and 13.93 ± 0.92 (ΔA845nm/ΔRIU) respectively. GO film over BPOF was stable even after incubation of the probes in the alcohols over 12 h. In addition, GO-BPOF probes were able to tolerate acetone environment for a prolonged duration of 30 min as opposed to 10 min in case of the bare probes due to improved chemical resistance. Hence, the GO-BPOF could potentially be utilized as a sensitive RI sensor not only for aqueous solutions but also for reactive organic solvents such as alcohols and acetone which are known to damage the PMMA surface.