Controlled Synthesis of Gold Nanoparticles on Fluorescent Nanodiamond via Electron-Beam-Induced Reduction Method for Dual-Modal Optical and Electron Bioimaging

Hybrid nanoparticles are emergent nanomaterials that combine particles with different characteristic properties to enhance their original functions or modulate their original physical or chemical properties for application in catalysis, sensing, and imaging. Fluorescent nanodiamonds (fNDs) have recently become more attractive for bioimaging because of their characteristic physicochemical properties and biocompatibility. Their wide applicability in bioimaging has been utilized in the single-particle tracking of biomolecules, local environmental sensors in cells, and stem cell tracking in tissues. However, the use of fNDs as multiscale spatial mapping probes for multiple biomolecules and cells in optical and electron microscopy techniques has been limited because of their broad fluorescence spectrum and composition of mainly light elements (C, O, H, N, etc.). On the other hand, metal nanoparticles (metal NPs) with unique photonic properties have been employed as functional labeling probes in bioimaging. Therefore, an efficient synthesis strategy to produce fND/metal NP nanocomposites with regulated shapes is required to develop molecular and cellular bioimaging probes with simultaneous use in multiple imaging techniques. Here, we report the synthesis of dual-modal hybrid gold NP–fND (Au-ND) nanoparticles with a mean diameter of less than 20 nm using an electron-beam-induced reduction method. The resultant Au-NDs exhibited stable Au-NP-induced plasmonic modulation of fluorescence lifetimes in cellular environments, which is useful for fluorescence lifetime imaging microscopy to detect multiple molecules or cells. Furthermore, Au NPs modified on fNDs function as surrogate markers with sub-10 nm spatial resolution for electron microscopy in mammalian cells. Our findings indicate that the electron-beam reduction method will enable us to make simplified formations of metal NPs with characteristic plasmonic structures on fNDs for multimodal bioimaging probes

Direct Synthesis of Carbon–Molybdenum Carbide Nanosheet Composites via a Pseudotopotactic Solid-State Reaction

We report the solid-state reaction of MoO₂ nanosheets, obtained from the soft-chemical delamination of Na_0.9Mo₂O₄, into metallic Mo₂C single layers that constitute a new family of versatile carbide nanosheets. This so-called pseudotopotactic reaction, i.e., conversion from nanosheet to nanosheet, is aided by the use of cationic polymers as binders for the film growth based on electrostatic self-assembly. Compared to Mo₂C in the bulk form, 2D anisotropic Mo₂C sheets having a larger surface-area-to-volume ratio are of significant use in potential electrochemical applications, and it is also worth noting that the thickness of Mo₂C sheets can be controlled in the nanometer range by altering the stacking number of the precursor nanosheets