Near-Field Nanoscopic Terahertz Imaging of Single Proteins

Terahertz (THz) biological imaging has attracted intense attention due to its capability of acquiring physicochemical information in a label-free, noninvasive, and nonionizing manner. However, extending THz imaging to the single-molecule level remains a challenge, partly due to the weak THz reflectivity of biomolecules with low dielectric constants. Here, the development of graphene-mediated THz scattering-type scanning near-field optical microscope for direct imaging of single proteins is reported. Importantly, it is found that a graphene substrate with high THz reflectivity and atomic flatness can provide high THz contrast against the protein molecules. In addition, a platinum probe with an optimized shaft length is found enabling the enhancement of the amplitude of the scattered THz near-field signals. By coupling these effects, the topographical and THz scattering images of individual immunoglobulin G (IgG) and ferritin molecules with the size of a few nanometers are obtained, simultaneously. The demonstrated strategy thus opens new routes to imaging single biomolecules with THz.

Automated summary

A graphene-mediated THz scattering-type scanning near-field optical microscope is developed for direct imaging of single proteins, demonstrating that a graphene substrate with high THz reflectivity and atomic flatness provides high THz contrast against protein molecules. The use of an optimized length platinum probe enhances the amplitude of scattered THz near-field signals, allowing the topographical and THz scattering images of individual IgG and ferritin molecules with a few nanometers in size to be obtained simultaneously. This strategy opens up new avenues for imaging single biomolecules with THz.