Extreme Enhancement of Single-Molecule Fluorescence from Porphyrins Induced by Gold Nanodimer Antennas.

Porphyrins are typically weak emitters, which presents challenges to their optical detection by single-molecule fluorescence microscopy. In this contribution, we explore the enhancement effect of gold nanodimer antennas on the fluorescence of porphyrins in order to enable their single-molecule optical detection. Four meso-substituted free-base porphyrins were evaluated: two cationic, one neutral, and one anionic porphyrin. The gold nanodimer antennas are able to enhance the emission from these porphyrins by a factor of 10-10 increase in the maximum detected photon rates. This extreme enhancement is due to the combination of an antenna effect on the excitation rate that is estimated to be above 10-fold and an emission efficiency that corresponds to an increase of 2-10 times in the porphyrin's fluorescence quantum yield.