Kei Hosomi

Electron beam excitation assisted (EXA) optical microscopy has been developed to establish label-free imaging with sub-diffraction limit resolution under ambient atmosphere. To improve the performance of the EXA microscope, a Gd³⁺-doped YAlO₃ luminescent thin film was fabricated on a LaAlO₃ layer. The existence of the LaAlO₃ layer enhanced the intensity of cathodoluminescence (CL) of the 4f-4f transition in Gd³⁺ ions by an order of magnitude as well as inducing a broad emission related to oxygen vacancies. The improvement of the crystallinity of the YAlO₃ matrix increased the CL intensity. We demonstrated the possibility of YAlO₃:Gd³⁺/LaAlO₃ luminescent thin film as an improved optical probe for EXA microscopy.

Crystallography has been the routine technique for studying high-resolution structures of proteins for over five decades. A major bottleneck in structure determination of macromolecules is obtaining crystals of a size and quality suitable for single-crystal X-ray crystallography experiments. Many challenging proteins either fail to grow into crystals or fail to grow into crystals of a size suitable for obtaining high-resolution structures using conventional X-ray crystallography. When it comes to smaller crystals, they can be used either for seeding to get larger crystals or for serial crystallography and electron diffraction for obtaining the structures. For both purposes, a limiting step is to non-invasively image such small crystals of sub-micrometre dimensions and to screen the conditions where such crystals prevail. Here we use cathodoluminescence-based (CL-based) nanoscopy to image protein nanocrystals. We show that crystals of micrometre and submicrometre dimensions can be non-invasively imaged by the CL-based nanoscope. The results presented here demonstrate the feasibility of non-invasive imaging of protein crystals with sub-100 nm resolution.