Surface plasmons on metal nanostructures have been found to affect emission of nearby fluorophores,increasing the radiative decay rate of the excited fluorophores,thus enhancing the fluorescence intensity.This phenomenon is called metal-enhanced fluorescence(MEF)and has been reported for various organic fluorophores and quantum dots proximal to gold or silver substrates or other metal nanostructures(1).It has also been found that the metal nanoparticles(NPs)can affect fluorescence intensity,which mostly depends on the distance between the metal nanostructures and fluorophores(2).