Label-Free Chemical Nano-Imaging of Intracellular Drug Binding Sites.

Optical microscopy has a diffraction limited resolution of about 250 nm. Fluorescence methods (e.g. PALM, STORM, STED) beat this, but they are still limited to 10 s of nm, and the images are an indirect pointillist representation of only part of the original object. Here we describe a way of combining a sample preparation technique taken from histopathology, with a probe-based nano-imaging technique, (s SNOM) from the world of Solid State Physics. This allows us to image subcellular structures optically, and at a nanoscale resolution that is about 100 x better than normal microscopes. By adding a tuneable laser source, we also demonstrate mid-infrared chemical nano-imaging (MICHNI) in human myeloma cells and we use it to map the binding sites of the anti cancer drug bortezomib to less than 10 zL sized intracellular components. MICHNI is label free and can be used with any biological material and drugs with specific functional chemistry. We believe that its combination of speed, cheapness, simplicity, safety and chemical contrast promises a transformative impact across the life sciences.