LPFG sensor for rapid and accurate in-situ detection of H2O2

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To achieve online, rapid, selective, and accurate detection of H 2 O 2 in UV/H 2 O 2 -based photo-oxidative processes for optimizing •OH production, this study developed a long-period fiber grating (LPFG)-based H 2 O 2 sensor using a graphene oxide (GO)-loaded two-line ferrihydrite (2L-Fht) nanozyme. The GO/2L-Fht sensing layer was synthesized via surface precipitation and immobilized onto the grating surface through a combination of chemical bonding and physical adsorption techniques. Acting as a peroxidase-like nanozyme with high enzymatic activity over a wide pH range, 2L-Fht catalyzes the decomposition of H 2 O 2 , releasing water molecules. GO interacts with these water molecules, altering its effective refractive index and inducing a resonance wavelength shift in the LPFG transmission spectrum. The H 2 O 2 concentration was determined by monitoring the wavelength shift. The effects of doping content, coating thickness, and the pH of the solution on sensor performance were investigated. The results demonstrated at a 2L-Fht doping content of 25 wt%, a coating thickness of 958 nm, and a pH of 7.0, the sensor achieved sensitivities of 95.18 and 285 pm/lg( c ) for H 2 O 2 concentration ranges of 10⁻ 8 to 10⁻ 2 M and 0.01 to 1 M, respectively. Additionally, it exhibited a detection limit as low as 3.99 nM and a response time of 6–14 s. The sensor also exhibited high selectivity and repeatability. This study presents the first use of GO/2L-Fht composites for H 2 O 2 sensing, offering an effective approach for rapid and sensitive detection across a pH range of 5–9 and broadening the applications of fiber optic sensing technology.