Nanoparticle core size and spacer coating thickness-dependence on metal-enhanced luminescence in optical oxygen sensors.

Metal-enhanced luminescence (MEL) originated from near field interactions of luminescence with the surface plasmon resonance (SPR) of nearby metallic nanoparticles (NPs) is an effective strategy to increase luminescence detection sensitivity in oxygen sensors. Once the excitation light induces SPR, the generated enhanced local electromagnetic filed will result in an enhanced excitation efficiency and an increased radiative decay rates of luminescence in close proximity. Meanwhile, the nonradioactive energy transfer from the dyes to the metal NPs, leading to emission quenching, can also be affected by their separation. The extent of the intensity enhancement depends critically on the particle size, shape and the separation distance between the dye and the metal surface. Here, we prepared core-shell Ag@SiO2 with different core sizes (35 nm, 58 nm and 95 nm) and shell thickness (5-25 nm) to investigate the size and separation dependence on the emission enhancement in oxygen sensors at 0-21% oxygen concentration. Intensity enhancement factors of 4-9 were observed with a silver core size of 95 nm and silica shell thickness of 5 nm at 0-21% O2. In addition, the intensity enhancement factor increases with increasing core size and decreasing shell thickness in the Ag@SiO2-based oxygen sensors. Using Ag@SiO2 NPs result in brighter emission throughout the 0-21% oxygen concentration. Our fundamental understanding of MEP in the oxygen sensors provides us the opportunity to design and control efficient luminescence enhancement in oxygen and other sensors. .