Protein layers formed on solid surfaces have a wide range of applications in the field of biosensing and biomaterials. High-resolution characterization of the morphological structures of protein forms in the process of developing protein layers has significant implications for the control of the layer’s quality as well as for the evaluation of the layer’s performance. However, it remains challenging to precisely characterize all possible morphological structures of protein in various forms. For example, although atomic force microscopy (AFM) has excellent performance in surface imaging, it fails to provide subsurface information of a protein layer.

Recently, Huabin Wang’s group (Chongqing Institute of Green and Intelligent Technology (CIGIT), the Chinese Academy of Sciences) and Jiang Li’s group (Institute of Materials Biology, Shanghai University) have jointly established a nanometer resolution terahertz morphology reconstruction microscopy (THz-MRN) technology having both surface and subsurface detection capabilities. They firstly developed a multilayer finite dipole model for a thin layer, then established a method to reconstruct the three-dimensional morphology structure of the sample based on the sample’s THz near-field image, and finally achieved the nanometer-resolved 3D morphological image of the sample. They demonstrated this technology by measuring single protein molecules, protein networks, protein monolayers and composite protein layers. The established THz-MRN has label-free and nondestructive characters, and both surface and subsurface detection capabilities. The lateral resolution of THz-MRN is comparable to that of AFM while its vertical resolution is about 0.5 nm. THz-MRN provides a novel and important approach for the study of biomolecules, functional materials, and semiconductor devices.

The above work was published as an article in ACS Nano titled "Near-Field Terahertz Morphological Reconstruction Nanoscopy for Subsurface Imaging of Protein Layers". Assistant Professor Zhongbo Yang from CIGIT is the first author, while Professors Huabin Wang and Jiang Li are corresponding authors. This work was supported in part by the National Key Research and Development Program of China, the National Natural Science Foundation of China, the University of Chinese Academy of Sciences Supported Program for Tackling Key Problems in Science and Technology, and the Natural Science Foundation of Chongqing.

Previously, they have achieved near-field THz nanoscopic imaging of single proteins (e.g., immunoglobulins and ferritin), and reported the results in Small.

Related paper links:

https://pubs.acs.org/doi/10.1021/acsnano.3c12776

https://onlinelibrary.wiley.com/doi/10.1002/smll.202005814