PNNL

Abstract

A new approach is demonstrated for simultaneous topographic and spectroscopic imaging applying near-field optics (NSOM) with spatial resolution beyond the optical diffraction-limit. The method combines atomic force microscopy (AFM) in the metallic-tip tapping mode and near-field scanning confocal fluorescence lifetime imaging microscopy (FILM). The AFM metallic tip was formed by sputter-coating a Si tapping mode tip with Au to form a spherulitic shape at the tip apex, allowing a high local field enhancement under laser illumination, which was necessary for a strong optical signal. A simulation used to finite element method (FEM) to further evaluate the near-field enhancement originating from the metallic Au-coated AFM tapping mode tip. We have demonstrated that spatially mapping the change in fluorescence lifetime and intensity is a promising approach to semi-quantitative and chemically specific imaging at AFM spatial resolution. The spherulitic Au-coated AFM tip not only gives adequate spatial AMF tapping-mode imaging spatial resolution but is apparently “environmentally friendly” to soft samples, such as polymeric dye-labeled nano-spheres and even biological specimens like POPO-3 labeled DNA.