Efficient Peroxide Nanosensors via Both Optical Fluorescence and Second Harmonic Generation (SHG) Conversion Processes

The scope of using cerium oxide–gold nanoparticles (CeO₂–Au NPs) as an optical sensor is studied via the fluorescence quenching technique. Under violet excitation, ceria NPs have a strong emission in the visible region (~530 nm), which clearly proves its strong fluorescent behavior. Here, Au NPs are embedded in situ with CeO₂ NPs. In addition, the second harmonic generation (SHG) of poly{1-[p-(3′-carboxy-4′-hydroxyphenylazo)benzenesulfonamido]-1,2-ethandiyl, sodium salt} (PCBS) and its fluorescence response with light emitting diode (LED) excitation at 780 nm were studied. The Stern–Volmer constant of PCBS in peroxide detection is 0.0987 M⁻¹, lower than the value of ceria, which is 0.1419 M⁻¹. Afterwards, the system is applied in the field of peroxide sensing in aqueous media. The fluorescence intensity is found to be affected by the addition of peroxides into CeO₂-Au NPs. The Stern–Volmer quenching constants were found to be 0.0987 M⁻¹ for PCBS, 0.1419 M⁻¹ for undoped ceria, and 0.1763 M⁻¹ for Au-doped ceria, indicating a 26.72% enhancement in sensitivity. The sensitivity of ceria NPs in peroxide quencher detection is found to be enhanced considerably by the addition of Au NPs. This is because of the plasmonic resonance of Au NPs as it is optically coupled with the fluorescence emission spectrum of ceria. The bandgap of ceria is also found to be decreased by the addition of Au NPs, which is due to the creation of more oxygen vacancies inside the nonstoichiometric crystalline structure of ceria. The sensitivity of the optical sensing material, ceria–gold NPs with added peroxide, is characterized by the Stern–Volmer constant and is found to be 0.1763 M⁻¹ which is higher than the case of using ceria NPs only. Ceria–gold NPs with enhanced optical sensitivity can be employed as an optical sensing host for peroxides, which plays a major role in many important applications such as biomedicine and water quality monitoring. This work introduces a novel dual-mode optical sensing platform by integrating the SHG response of PCBS thin films and the plasmon-enhanced fluorescence quenching behavior of Au-doped CeO₂ nanoparticles. The combined system demonstrates a 26.72% increase in peroxide sensitivity compared with pure ceria, making it a promising approach for efficient, low-cost detection in aqueous environments.