Broad Wavelength Range Metal-Enhanced Fluorescence Using Nickel Nanodeposits

We describe the use of surface-deposited nickel nanoparticles to enhance the fluorescence signatures of fluorophores. Different density Ni nanoparticulate substrates were fabricated and characterized using both AFM and optical absorption techniques. When fluorophores were placed in close proximity to the substrates, metal-enhanced fluorescence (MEF) was observed. The wavelength dependence of the metal-enhanced fluorescence corresponded with numerical finite-difference time-domain simulations also showing a broad range (500-800 nm) for the enhanced electric field of Ni nanoparticles as compared with traditionally ≈400 to 500 nm for the widely used Ag nanoparticles. This broad wavelength range for an enhanced electric field enables nickel nanoparticles to enhance near-field dipoles in the visible to the infrared region. In addition, the decay times of fluorophores were also reduced near the Ni substrates, suggesting both an enhanced electric field and a plasmon-coupling component are the mechanisms for fluorescence enhancement, similar to MEF substrates made from silver, copper, and gold nanoparticles. Our results show that nickel nanoparticles are suitable for enhancing near-infrared fluorescence, to a similar degree as Ag nanoparticles, and, therefore, are particularly applicable to the many whole blood biological assays in use today.