We have investigated the effect of metal induced energy transfer from gold nanoaperture to fluorescence lifetime. We changed the orientation and position of dipole inside various diameter of nanohole and calculated relative lifetime by COMSOL Multiphysics and MATLAB. For the experiment, confocal microscopy setup was customized with blue laser at 479 nm and the nanoaperture was fabricated by both focused ion beam and e-beam lithography. Also, HPTS fluorescent dye in PVA solution was deposited on the nanoapertures by spin coating method instead of water droplets to avoid the effect from the film side and improve the contrast of the lifetime image. While the diameter of nanoapertures changed from 70 to 200 nm with 50 and 100 nm height, the maximum value of fluorescence lifetime tended to be proportional to the diameter and height due to energy transfer between dipole and metal. The maximum lifetime was 1.8 ns at 200 nm diameter which corresponded with calculation results. However, the lifetime difference between two heights was not linear tendency. The lifetime reduction factor was of about almost 10 for a 70 nm nanohole, and 3 for a 200 nm nanohole which was a maximum of 3 in the case of droplet. It is possible to distinguish the size of the nanohole using the lifetime reduction even at a scale below the diffraction limit and applied to single biomolecule detection.
|