This study investigates the enhancement of single molecule fluorescence using a gold nanoparticle as an optical nano-antenna. The researchers used scanning probe technology to position the nanoparticle in front of a single molecule with nanometer precision and observed a 20-fold increase in fluorescence intensity and a 20-fold shortening of the excited state lifetime. They compared their results with three-dimensional calculations to understand the contributions of excitation enhancement, spontaneous emission modification, and quenching. They also provided direct evidence for the role of the nanoparticle's plasmon resonance in modifying molecular emission. Gold nanoparticles support plasmon resonances that can enhance the excitation and emission of molecules. The researchers found that the fluorescence signal depends on the position and orientation of the molecule relative to the nanoparticle. They used a scanning shear-force stage mounted on an inverted optical microscope to position the nanoparticle and measure the fluorescence. The results showed that the fluorescence intensity was significantly enhanced when the nanoparticle was in the near field of the molecule, and the excited state lifetime was shortened. The study also demonstrated that the nanoparticle's plasmon resonance plays a crucial role in the enhancement process. The researchers performed three-dimensional calculations to compare their experimental results with theoretical predictions. They found that the calculated values matched the experimental data well, except for a deviation in a region of 20-50 nm, which they attributed to the effect of the pT-air interface. The study concludes that the near-field coupling of a single molecule with a gold nanoparticle can quantitatively and controllably enhance single molecule fluorescence. The results demonstrate the potential of using a gold nanoparticle as a nano-antenna for various applications, including the detection of weakly fluorescing systems.This study investigates the enhancement of single molecule fluorescence using a gold nanoparticle as an optical nano-antenna. The researchers used scanning probe technology to position the nanoparticle in front of a single molecule with nanometer precision and observed a 20-fold increase in fluorescence intensity and a 20-fold shortening of the excited state lifetime. They compared their results with three-dimensional calculations to understand the contributions of excitation enhancement, spontaneous emission modification, and quenching. They also provided direct evidence for the role of the nanoparticle's plasmon resonance in modifying molecular emission. Gold nanoparticles support plasmon resonances that can enhance the excitation and emission of molecules. The researchers found that the fluorescence signal depends on the position and orientation of the molecule relative to the nanoparticle. They used a scanning shear-force stage mounted on an inverted optical microscope to position the nanoparticle and measure the fluorescence. The results showed that the fluorescence intensity was significantly enhanced when the nanoparticle was in the near field of the molecule, and the excited state lifetime was shortened. The study also demonstrated that the nanoparticle's plasmon resonance plays a crucial role in the enhancement process. The researchers performed three-dimensional calculations to compare their experimental results with theoretical predictions. They found that the calculated values matched the experimental data well, except for a deviation in a region of 20-50 nm, which they attributed to the effect of the pT-air interface. The study concludes that the near-field coupling of a single molecule with a gold nanoparticle can quantitatively and controllably enhance single molecule fluorescence. The results demonstrate the potential of using a gold nanoparticle as a nano-antenna for various applications, including the detection of weakly fluorescing systems.