High-Performance Oxygen Sensing Films with Enhanced Quenching Efficiency and Fluorescence Stability via FITC–PtOEP FRET and Imidazole Modification

Fluorescence resonance energy transfer (FRET) was implemented in a photonic crystal-structured oxygen sensing film by incorporating fluorescein isothiocyanate (FITC) with platinum octaethylporphyrin (PtOEP). The highest Stern-Volmer quenching constant (K_SV = 20.20 ± 0.25) and maximum quenching ratio (21.81 ± 0.21) were achieved at a PtOEP:FITC molar ratio of 1:1. Compared to the control, the K_SV and maximum quenching ratio increased by 56.8% and 48.4%, respectively. Additionally, imidazole was introduced into the oxygen-sensing film via a casting method. The results demonstrated that imidazole effectively modulates the energy transfer efficiency between oxygen molecules and PtOEP. Under 20% O₂ and 100% O₂ atmospheres, the fluorescence intensity of the imidazole-modified film increased by 18.4% and 52.4%, respectively. Furthermore, imidazole provided excellent protection for PtOEP, yielding a fluorescence retention rate of 99.77% ± 0.18%.