Monitoring the dynamics of proteins in live cells on appropriate spatiotemporal scales may provide key information regarding long-standing questions in molecular and cellular regulatory mechanisms. However, tools capable of imaging the conformational changes over time have been elusive. Here, we present a single-molecule stroboscopic imaging probes by developing gyroscopic plasmonic nanoparticles, allowing for replication of protein–protein interactions and the conformational dynamics based on rotational and lateral velocities. This study fundamentally monitors the rotational motion of a membrane protein, epidermal growth factor receptor (EGFR), to decipher undiscovered structural dynamics in live cells without any molecular perturbations. This method offers a strategy to visualize assemblies and conformational changes, and provides unique insights into the mechanism underlying the molecular dynamics for receptors.
Spectroelectrochemical analysis using surface plasmon scattering can provide a great deal of information on nucleation and growth mechanisms for nanoscale materials. In this study, we combined a transparent electrochemical thin-layer cell with dark-field spectroscopy to resolve the Cu deposition process on individual Ag nanocubes. During the deposition process, both electrochemical responses and plasmon scattering images were obtained, which were directly correlated with reduction kinetics and morphological evolution, respectively. By applying linear sweep potentials with variable sweep rates, three distinct morphologies, atop tetrapods, dendritic spheres, and multiple cubes, were uniformly generated. The atop tetrapods were formed at the bulk deposition potential, −0.34 V. At lower potential sweep rates, however, the maximum scattering peak wavelength and intensity, converted from the plasmon scattering images, significantly changed in the low potential region of −0.23 to −0.33 V. The plasmon scattering simulation and scanning electron microscopy images at the fixed potentials provided evidence that nucleation occurred on the Ag surface in this potential range. Such an underpotential deposition of Cu on Ag was hardly observed in bulk but was critical to induce the distinct morphology in the nanoscale. Based on these observations, the deposition mechanism was understood in detail: the atop tetrapods were generated by selective bulk deposition, whereas the dendritic spheres and multiple cubes were formed by underpotential nucleation and growth aided by a surfactant. This spectroelectrochemical tool with dark-field spectroscopy provides real-time and in situ analysis under the actual reaction conditions and therefore, would be versatile to analyze various heterogeneous reaction systems.
Cells use gaseous molecules such as nitric oxide (NO) to transmit both intracellular and intercellular signals. In principle, the endogenous small molecules regulate physiological changes, but it is unclear how randomly diffusive molecules trigger and discriminate signaling programs. Herein, it is shown that gasotransmitters use time‐dependent dynamics to discriminate the endogenous and exogenous inputs. For a real‐time stimulation of cell signaling, we synthesized a photo‐cleavable metal–nitrosyl complex, [CoIII(MDAP)(NO)(CH3CN)]2+ (MDAP=N,N′‐dimethyl‐2,11‐diaza[3,3](2,6)pyridinophane), which can stably deliver and selectively release NO with fine temporal resolution in the cytosol, and used this to study the extracellular signal‐regulated kinases (ERKs), revealing how cells use both exogenous and endogenous NO to disentangle cellular responses. This technique can be to understand how diverse cellular signaling networks are dynamically interconnected and also to control drug delivery systems.
The galvanic replacement reaction has recently been established as a standard protocol to create complex hollow structures with various compositions and morphologies. In the present study, the structural evolution of Ag nanocubes with Au precursors is monitored at the single-particle level by means of ex situ and in situ characterization tools. We explore two important features distinct from previous observations. First, the peak maximum of localized surface plasmon resonance (LSPR) spectra abruptly shifts at the initial stage and reaches a steady wavelength of ∼600 nm; however, the structure continuously evolves to yield a nanobox even during the late stages of the reaction. This steady wavelength results from a balance of the LSPR between the red-shift by the growth of the inner cavity and the blue-shift by the deposition of Au on the interior, as confirmed by theoretical simulations. Second, the change in morphology at different temperatures is first analyzed by both ex situ and in situ monitoring methods. The reaction at 25°C forms granules on the surface, whereas the reaction at 60°C provides flat and even surfaces of the hollow structures due to the large diffusion rate of Ag atoms in Au at a higher temperature. These plasmon-based monitoring techniques have great potentials to investigate various heterogeneous reaction mechanisms at the single-particle level. ■ INTRODUCTIONFor the past several decades, metal nanostructures have been extensively studied due to their unique physical and chemical properties and versatile applications in many areas. To control the properties of metal nanostructures so as to make them suitable for specific applications, the creation of complex nanostructures with multiple components and high-dimensional morphologies has been attempted, such as core−shell, 1,2 hollow, 3,4 and branched nanoparticles. 5,6 For the fabrication of these nanostructures, solid-state chemical reactions on the nanoscale are commonly applied, including galvanic replacement, 7,8 void formation via the Kirkendall effect, 9 and cationic and anionic exchanges 10 as well as the induction of kinetic growth during the synthesis step. In particular, galvanic replacement has been established as a standard method to make complex hollow nanostructures with a variety of compositions and morphologies.Galvanic replacement is basically a redox process between two metals with distinct reduction potentials. Oxidation occurs on the metal with a low reduction potential, and the reduction and deposition concomitantly occur on the other metal with a high reduction potential. The replacement reaction is known as a major cause of the corrosion of metal surfaces in the bulk form, and Xia et al. revitalized it as a simple and versatile route for the generation of metal hollow nanostructures. 11 The formation mechanism of this reaction was elucidated through a change in the morphology as observed in TEM images along the reaction progress. These outcomes included the generation of a specific spot, a continuous hollow formation, mor...
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