Two-Color Metal-Enhanced Fluorescence Using Gold Slotted Nanogratings

We demonstrate enhanced fluorescence from multiple types of fluorescent molecules on a single metal enhancing fluorescence (MEF) substrate. Two fluorescent molecules were simultaneously enhanced using gold wire nanogratings. MEF substrates support two mechanisms of fluorescence enhancement: enhanced excitation of the fluorescent molecules and an increase in the quantum yield through a reduction in excited state lifetime. Gold wire nanogratings with a period of 500 nm were fabricated such that they supported a range of surface plasmon wavelengths that spanned the visible spectrum. The fluorescent molecules were chosen such that their absorption and emission spectrum overlapped minimally. The fluorescent molecules were excited with different excitation lasers and both showed enhanced emission consistently over a broad range of wavelengths. Because of the periodicity of the gratings, the enhanced fluorescence beamed out of the sample at angles determined by the wavelength dependent dispersion relationship for the surface plasmons, potentially simplifying fluorescence detection. Both molecules showed similar enhancements, despite different excitation efficiencies.