Novel Detection of Non-absorbing Molecules by Optical Near-field Induced Thermal Lens Microscopy

This study reports a novel detection method of Thermal Lens Microscopy (TLM), in which the excitation of analytes is manipulated by Optical Near-Field (ONF) generated on nanostructures. Owning to the property of apparent higher energy than incident photons, herein the ONF allows the electronic excitation of molecules even though the energy of incident light is lower than absorption energy of molecules. As a result, the detection of UV-absorbing molecules has been realized with visible excitation. Our result promises important implications in detection of biomolecules, which usually have absorption in UV range. It is also worthy to note that the present work is novel in using ONF on nanostructures of non-metal materials, which is conceptually different from the plasmonic field enhancement on metal nanoparticles. This study is expected to open a new perspective for ONF-induced spectroscopies realized by top-down nanofabrication.