Results

Initially, we evaluated the capacity of our approach to translate and position a microbead across an extended sample. In this case, we used a structure consisting of the letters “iit” fabricated on a gold-coated glass substrate by FIB lithography. Notably, each letter contained a sub-structure comprised of lines with a periodicity of 380 nm (Fig. 1a). An image acquired using a 50x long working distance objective (NA 0.5, working distance 10.3 mm, Olympus LMPLANFL) with transmitted 405 nm light from a blue LED is presented in Fig. 1b. We selected this particular color since it offered higher contrast and spatial resolution than white light. As expected, at these conditions the “iit” letters can be clearly resolved, but not so the lines within each letter. Note that the diffraction limit in this case is~ 405 nm, above the periodicity of the sub-structure. When using the microbead, though, the periodic lines can be resolved (Fig. 1c). In this case, the distance between microbead and sample was maintained at 50 nm. This separation was found to be the optimal tradeoff between image contrast and possibility to freely translate the nanojet while preventing the adhesion of the microbead to the sample (see Supplementary Figure 1 and Supplementary Movie 1). The image was collected with the objective focal plane located 4.5 µm below the microbead base, thus the formed image was virtual. More importantly, as shown in Supplementary Movie 2, the AFM cantilever enables to easily translate the microbead across the “iit” letters, providing a locally magnified image with enhanced resolution at user-defined positions.