Antenna Enhanced Infrared Photoinduced Force Imaging in Aqueous Environment with Super-Resolution and Hypersensitivity

Tip-enhanced infrared(IR)spectra and imaging have been widely used in cutting-edge studies for the in-depth understanding of the composition,structure,and function of interfaces at the nanoscale.However,molecular monolayer sensitivity has only been demonstrated at solid/gas interfaces.In an aqueous environment,reduced sensitivity limits the practical applications of tip-enhanced IR nanospectroscopy.Here,we present an approach to hypersensitive nanoscale IR spectra and imaging in an aqueous environment with a combination of photoinduced force(PiF)microscopy and resonant antennas.

Substructure imaging of heterogeneous nanomaterials with enhanced refractive index contrast by using a functionalized tip in photoinduced force microscopy

The opto-mechanical force response from light-illuminated nanoscale materials has been exploited in many tip-based imaging applications to characterize various heterogeneous nanostructures.Such a force can have two origins:thermal expansion and induced dipoles.The thermal expansion reflects the absorption of the material,which enables one to chemically characterize a material at the absorption resonance.The induced dipole interaction reflects the local refractive indices of the material underneath the tip,which is useful to characterize a material in the spectral region where no absorption resonance occurs,as in the infrared(IR)-inactive region.Unfortunately,the dipole force is relatively small,and the contrast is rarely discernible for most organic materials and biomaterials,which only show a small difference in refractive indices for their components.In this letter,we demonstrate that refractive index contrast can be greatly enhanced with the assistance of a functionalized tip.With the enhanced contrast,we can visualize the substructure of heterogeneous biomaterials,such as a polyacrylonitrile-nanocrystalline cellulose(PAN-NCC)nanofiber.From substructural visualization,we address the issue of the tensile strength of PAN-NCC fibers fabricated by several different mixing methods.Our understanding from the present study will open up a new opportunity to provide enhanced sensitivity for substructure mapping of nanobiomaterials,as well as local field mapping of photonic devices,such as surface polaritons on semiconductors,metals and van der Waals materials.