Platinum plasmonic nanostructure arrays for massively parallel single-molecule detectionbased on enhanced fluorescence measurements

Abstract

We fabricated platinum bowtie nanostructure arrays producing fluorescence enhancementand evaluated their performance using two-photon photoluminescence and single-moleculefluorescence measurements. A comprehensive selection of suitable materials was exploredby electromagnetic simulation and Pt was chosen as the plasmonic material forvisible light excitation near 500 nm, which is preferable for multicolor dye-labelingapplications like DNA sequencing. The observation of bright photoluminescence (λ = 500–600 nm) from each Pt nanostructure, induced by irradiation at 800 nm with a femtosecondlaser pulse, clearly indicates that a highly enhanced local field is created nearthe Pt nanostructure. The attachment of a single dye molecule was attemptedbetween the Pt triangles of each nanostructure by using selective immobilizationchemistry. The fluorescence intensities of the single dye molecule localized on thenanostructures were measured. A highly enhanced fluorescence, which was increasedby a factor of 30, was observed. The two-photon photoluminescence intensityand fluorescence intensity showed qualitatively consistent gap size dependence.However, the average fluorescence enhancement factor was rather repressed even inthe nanostructure with the smallest gap size compared to the large growth ofphotoluminescence. The variation of the position of the dye molecule attached to thenanostructure may influence the wide distribution of the fluorescence enhancement factorand cause the rather small average value of the fluorescence enhancement factor.