Abstract
The near infrared (NIR) fluorescence enhancement by local surface plasmon resonanoce from arrayed gold (Au) nanoblocks was investigated by NIR fluorescent dyes, IR780, immobilized in hydrophobic DNA thin film on glass substrates, to clarify the gap mode effect on the fluorescence enhancement. In the substrate with Dimer type Au nanoblock arrangement, average total fluorescence intensity was larger by 10.0, 2.4, and 12.4 times for non-polarized, P- and S- polarization as compared with that on a glass substrate alone, respectively. These findings suggested that enhancement of excitation light intensity at nanogap in the Dimer type Au nanoblock arrangement affected the fluorescence intensity. Average total fluorescence intensity, on the other hand, was smaller by 0.63 times as compared with that on a glass substrate alone in the checkerboard type Au array. It is suggested that the fluorescence quenching was caused by the energy transfer from the excited state of IR780 to Au nanoblocks or by the increased deactivation of excited dye molecules induced by resonance with Au nanoblocks at the checkerboard arrangement. We have firstly achieved the NIR fluorescence enhancement by LSPR due to the gap mode.
Highlights
Local surface plasmon from metal nano structures provides strong photon-molecule coupling fields [1], which markedly assist photochemical reaction such as photocatalysis [2], photovoltaic cell [3], photochromic reaction [4,5], and optical excitation process [6]
It is suggested that the fluorescence quenching was caused by the energy transfer from the excited state of IR780 to Au nanoblocks or by the increased deactivation of excited dye molecules induced by resonance with Au nanoblocks at the checkerboard arrangement
Checker board structure caused the fluorescence quenching rather than fluorescence enhancement, which means the fluorescence quenching originates from the energy transfer from the excited state of IR780 to Au nanoblocks or the increased deactivation of excited dye molecules induced by resonance with Au nanoblocks
Summary
Local surface plasmon from metal nano structures provides strong photon-molecule coupling fields [1], which markedly assist photochemical reaction such as photocatalysis [2], photovoltaic cell [3], photochromic reaction [4,5], and optical excitation process [6]. The. energy transfer from porphyrin to NIR fluorescent dyes along the DNA double helix was investigated upon excitation at the visible region in order to overcome these disadvantages [10]. We reported the application of confined and electric field enhanced light at surface plasmon resonance (SPR) condition to highly sensitive fluorescence detection of dyes in DNA ultrathin films deposited on a metal film and to high performance nitrogen oxides gas sensing [11]. These results demonstrated that DNA chain is one of the most powerful tools for nanoassemblies and will give novel concepts of materials design. We report the enhancement of NIR fluorescence intensity using the regularly arranged Au nanostructures with interaction between nanostructures, which show specific absorption in the NIR region to clarify the gap mode effect on the fluorescence enhancement
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