We describe a simple method of fabricating gold tips for tip-enhanced near-field optical microscopy using a single step direct current electrochemical etch. Smooth gold tips with a radius of curvature approximately 40 nm and with an aspect ratio suitable for shear force measurement have been produced in a few minutes. A detailed analysis of the etching process has enabled production of reproducible high quality tips. Near field images of single quantum dots using tips etched with this technique are shown.

We report modifications to the optical properties of fluorophores in the vicinity of noble metal nanotips. The fluorescence from small clusters of quantum dots has been imaged using an apertureless scanning near-field optical microscope. When a sharp gold tip is brought close to the sample surface, a strong distancedependent enhancement of the quantum dot fluorescence is observed, leading to a simultaneous increase in optical resolution. These results are consistent with simulations of the electric field and fluorescence enhancement near plasmonic nanostructures. Highly ordered periodic arrays of silver nanotips have been fabricated by nanosphere lithography. Using fluorescence lifetime imaging microscopy, we have created high-resolution spatial maps of the lifetime components of vicinal fluorophores; these show an order of magnitude increase in decay rate from a localized volume around the nanotips, resulting in a commensurate enhancement in the fluorescence emission intensity. Spatial maps of the Raman scattering signal from molecules on the nanotips shows an enhancement of more than five orders of magnitude.Keywords scanning near-field optical microscopy · ASNOM · fluorescence lifetime imaging · FLIM · plasmon · nanoparticle · Raman · SERS