High sensitivity detection of different pH ranges with rGO-nanocomposite coated eFBG sensor

In the proposed work, a highly sensitive reduced graphene oxide (rGO) coated etched fiber Bragg grating (eFBG) pH sensor is developed and characterized. To create the sensing probe, a nanocomposite layer of rGO is coated over the unclad area of the eFBG. The analysis of rGO material has been done using different characterization tools such as UV-VIS-NIR spectroscopy, x-ray diffraction (XRD), and field emission scanning electron microscopy (FESEM). Experiments are performed using pH samples ranging from pH 2 to pH 12 to validate the operational sensing range of the proposed sensor. The effectiveness of the proposed sensor is evaluated with various pH values by monitoring the shift in the resonance peak of the sensor's reflection spectrum in a real-time interrogation system. The sensor performs well in both low and high pH ranges, with a maximum sensitivity of 0.232 nm/pH at pH 12. Due to a shift in the rGO's optical band-gap at both low and high pH values in the samples, the sensor can detect minimal changes in concentration. In the reflected spectrum, the Bragg wavelength (λ _B) shifts as a result of the change in the refractive index. The λ _B is observed to change as the pH of the aqueous solution is changed experimentally. Its performance is shown to be minimally affected by the ambient temperature (in the range of 19-21^∘ C). The sensor also has the capacity for remote sensing, a quick response time, a small size, a low cost, a miniaturized probe, and the ability to reuse the probe.