The interest in optical properties of colloidal metals is driven by their applications to chemistry and optics. Metallic nanoparticles have the ability to enhance the local optical fields and change the spectroscopic properties of organic molecules as well as allow for design new optical devices. Metal-enhanced fluorescence (MEF) is yielding enormous opportunities for enhanced fluorescence sensing and imaging in microfluidics, lab-on-a-chip, clinical diagnostics, microarrays, and cellular applications. MEF is a through-space phenomenon relying on interaction of fluorophores with metallic nano-particles in the presence of excitation light. MEF can be utilized to produce new fluorometric devices with dramatically increased sensitivity.
We report on metal-enhanced fluorescence measured on a silicon surface with silver nanoparticles patterned with electron beam lithography. We employ a combinatorial approach, depositing silver particles ranging in size, shape, inter-particle spacing, and nominal thickness. Two nanoparticle shapes were investigated, square and triangular in cross section with side dimensions ranging from 50 nm to 130 nm and spaced at distances ranging from 150 nm to 390 nm center-to-center. The fluorescence enhancement of several fluorophores was measured with excitation sources consisting of an Ar ion laser at 488/514 nm and a HeNe laser at 633 nm. This approach allows an easy and direct comparison of the fluorescence enhancement to the particle size, shape, inter-particle spacing, and excitation wavelength.