Fig. 1. Scheme diagrams of HRP-coated fiber-optic SPR sensor and light transmission in fiber. (a) Internal environment of sensor without H₂O₂; (b) internal environment of sensor with H₂O₂

Fig. 2. Flowchart of fabrication of sensor

Fig. 3. Schematic diagram of sensor measurement system

Fig. 4. SEM images of surface topography. (a) Bare fiber; (b) polymerized polydopamine fiber; (c) gold-coated fiber; (d) secondary polymerized polydopamine fiber; (e) HRP-coated fiber; (f) phenol oxidation product attached fiber

Fig. 5. EDS energy spectra of optical fiber surface. (a) Bare fiber; (b) polymerized polydopamine fiber; (c) gold-coated fiber; (d) secondary polymerized polydopamine fiber; (e) HRP-coated fiber; (f) phenol oxidation product attached fiber

Fig. 6. Output spectra and sensitivity of prepared sensors under different polydopamine polymerization time and temperatures. (a) Output spectrum and (b) sensitivity of prepared sensors under different polydopamine polymerization time; (c) output spectrum and (d) sensitivity of prepared sensors under different polydopamine polymerization temperatures

Fig. 7. Output spectrum and sensitivity of prepared sensors under different AuNPs adsorption time. (a) Output spectrum; (b) sensitivity

Fig. 8. Output spectra and sensitivity of prepared sensors under different HRP concentration and fixation time. (a) Output spectrum and (b) sensitivity of prepared sensors under different HRP concentration; (c) output spectrum and (d) sensitivity of prepared sensors under different HRP fixation time

Fig. 9. Sensitivity, response time, repeatability, selectivity, and low limit of detection (LOD) of sensor. (a) Response sensitivity of sensor to phenol solution with and without H₂O₂ in internal environment during measurement of sensor (sampling interval is 300 s); (b) response time of sensor to 20 mg/L phenol solution; (c) effect of PPM on detection of 20 mg/L phenol solution; (d) selectivity and LOD of sensor for phenol solution (sampling interval is 300 s)