Diphenylalanine Nanotube Coated Fiber Bragg Grating for Methanol Vapor Detection

Etched fiber Bragg grating (EFBG) was coated with diphenilalanine nanotubes (DNT) to produce sensors capable of detecting methanol in methanol-ethanol blend vapors. The DNT was studied in two phases, hexagonal and orthorhombic, which were observed by Raman spectroscopy and scanning electron microscopy (SEM). The temperature transition between the phases was determined through small angle x-ray scattering (SAXS). Considering the methanol concentration in the vapor, the orthorhombic phase showed a sensitivity of -7.3 ± 0.8pm / (%v/v), which was 33 times greater than that observed for the hexagonal phase, with approximately the same response time. The maximum wavelength shift measured was -0.98 ± 0.02nm. Additionally, we proposed a mathematical model to describe the sensor's response, and we hypothesized the mechanisms that could lead to its nonlinear behavior.