Enhanced sensitivity near-field scanning optical microscopy at high spatial resolution

An apertureless near-field optical-imaging method is presented that achieves high spatial resolution as well as a ∼4000-fold increase in detection sensitivity, by exploiting the highly localized enhanced near-field interactions between the sample (e.g., Au nanospheres) and a sharp atomic force microscope tip under evanescent laser field illumination. This represents a general method for optical imaging at ⩽2 nm spatial resolution, and is applicable to both resonant (i.e., scattering) as well as nonresonant (i.e., fluorescence, Raman, etc.) spectroscopic methods.