Graphene Oxide Doped Alginate Coated Optical Fiber Sensor for the Detection of Perfluorooctanoic Acid in Water

A novel and easy to fabricate graphene doped alginate thin film (Alg/GO) capable of binding with perfluorooctanoic acid (PFOA) and working on the principle of a Fabry-Perot interferometry (FPI) type optical fiber sensor (OFS) is presented here. Utilizing a simple dip coating technique, the Alg/GO coating was deposited on the freshly cleaved fiber end-face followed by cross-linking in calcium chloride. The experimental results from two independent data analysis techniques, including Fourier-transform infrared (FTIR) spectroscopy and analytical adsorption tests were used to confirm that the developed graphene-doped alginates can adsorb PFOA. It was also found that GO-doped alginate coating adsorbs twice as much PFOA compared to alginate alone. Similarly, experimental results of the developed FPI sensor demonstrate the sensitivity to PFOA in aqueous solutions with a limit of detection (LOD) of 0.4 ppb and a non-linear correlation between 0 and 2 ppb with increasing concentrations of PFOA in water. The response time at this concentration was estimated to be 17 s, considering a thin film coating thickness of approximately 30
$\mu \text{m}$
as determined via imaging with the aid of differential interference contrast (DIC) microscopy. The relatively high sensitivity and ease of formation of the coating offer the potential for the future development of portable optical sensors for emerging environmental contaminants.