Oxidized Salicylaldoxime: A Candidate for Metal-Enhanced Fluorescence with Sensing Applications

Metal-enhanced fluorescence (MEF), especially originating from inexpensive copper, involving novel fluorophores, is an active area of research. Salicylaldoxime (SDX) was disclosed here as an efficient and cost-effective candidate for producing MEF. As a result of the reduction of Cu²⁺ to copper nanoparticles (CuNPs), SDX was oxidized to its quinone form. The in-situ-produced quinone exhibited MEF with in-situ-produced CuNPs. Uric acid quenched the fluorescence, while H₂O₂ restored the fluorescence exclusively. Tuning of MEF was done to design an H₂O₂ sensor with a linear detection range of 0-10⁻⁶ M and a limit of detection 1.74 × 10⁻⁷ M. The lightning rod effect and enhanced scattering cross-section (associated with aggregation) were pivotal for MEF, while the disintegration of particles with lower scattering cross-section was responsible for fluorescence quenching. This work may open a new window for identifying new fluorophores in the context of MEF, linked to environmental monitoring.