Probing structural changes in single enveloped virus particles using nano-infrared spectroscopic imaging - Fig 5

<p>(A) Nano-FTIR spectra of influenza virus particles at neutral pH (green) and at pH 5 (red). Topography and hyperspectral images of a virus particle at pH 7. Topography, and spectra obtained at two different points on the particle (A and B) (a). Near-field amplitude, A₂ (b and d) and phase φ₂ (c and e) images at frequencies 1400 and 1225 cm^-1 sliced from hyperspectral data. Scale bar 100 nm.</p

Probing structural changes in single enveloped virus particles using nano-infrared spectroscopic imaging

<div><p>Enveloped viruses, such as HIV, Ebola and Influenza, are among the most deadly known viruses. Cellular membrane penetration of enveloped viruses is a critical step in the cascade of events that lead to entry into the host cell. Conventional ensemble fusion assays rely on collective responses to membrane fusion events, and do not allow direct and quantitative studies of the subtle and intricate fusion details. Such details are accessible via single particle investigation techniques, however. Here, we implement nano-infrared spectroscopic imaging to investigate the chemical and structural modifications that occur prior to membrane fusion in the single archetypal enveloped virus, influenza X31. We traced in real-space structural and spectroscopic alterations that occur during environmental pH variations in single virus particles. In addition, using nanospectroscopic imaging we quantified the effectiveness of an antiviral compound in stopping viral membrane disruption (a novel mechanism for inhibiting viral entry into cells) during environmental pH variations.</p></div

Spatial evolution of virus particles when acidity changed from pH 7 to pH 5.

<p>Topography (black & white), and near-field amplitude (A₃) and phase (φ₃) images of four virus particles at pH 7 (a) and pH 5 (b) taken at 1225 and 1665 cm^-1. Scale bar 100 nm.</p

Schematic of s-SNOM nanoimaging and nano-FTIR setup.

<p>Schematic of s-SNOM nanoimaging and nano-FTIR setup.</p

Near-Field Surface Waves in Few-Layer MoS₂

Recently emerged layered transition metal dichalcogenides have attracted great interest due to their intriguing fundamental physical properties and potential applications in optoelectronics. Using scattering-type scanning near-field optical microscope (s-SNOM) and theoretical modeling, we study propagating surface waves in the visible spectral range that are excited at sharp edges of layered transition metal dichalcogenides (TMDC) such as molybdenum disulfide and tungsten diselenide. These surface waves form fringes in s-SNOM measurements. By measuring how the fringes change when the sample is rotated with respect to the incident beam, we obtain evidence that exfoliated MoS₂ on a silicon substrate supports two types of Zenneck surface waves that are predicted to exist in materials with large real and imaginary parts of the permittivity. In addition to conventional Zenneck surface waves guided along one interface, we introduce another Zenneck-type mode that exists in multilayer structures with large dissipation. We have compared MoS₂ interference fringes with those formed on a layered insulator such as hexagonal boron nitride where the small permittivity supports only leaky modes. The interpretation of our experimental data is supported by theoretical analysis. Our results could pave the way to the investigation of surface waves on TMDCs and other van der Waals materials and their novel photonics applications

Probing structural changes in single enveloped virus particles using nano-infrared spectroscopic imaging - Fig 4

<p>Nano-FTIR spectra of influenza virus particles from three different samples at neutral pH (a) and spectra from virus particles taken on day 1 and day 7 (b). Topography, near-field amplitude (A₃) and phase (φ₃) images of two influenza virus particles on day 1 and day 7 (c). Scale bar 100 nm.</p

Probing structural changes in single enveloped virus particles using nano-infrared spectroscopic imaging - Fig 3

<p>Topography, near-field amplitude (A₃) and phase (φ₃) images of several influenza virus particles i-(a), after compound 136 interaction (15 min) i-(b), followed by acid exposure i-(c). ii-(a-b) shows a different set of virus particles at neutral pH ii-(a) and ii-(b) shows the particles after acid exposure following compound 136 incubation (1 hr.). Scale bar 100 nm.</p

s-SNOM experimental setup and near-field infrared spectral images of influenza virus at pH 7.4.

<p>(a) schematic of the s-SNOM experiment, (b) topography of four viruses (scale bar is 100 nm), (c-e) near-field phase (φ₃) spectral images at three different frequencies. Line profiles of topography (f) and phase (g) representing the red broken lines shown in the topography (b) and phase (c, e) images.</p

Infrared Nanoimaging of Hydrogenated Perovskite Nickelate Memristive Devices

Solid-state devices made from correlated oxides, such as perovskite nickelates, are promising for neuromorphic computing by mimicking biological synaptic function. However, comprehending dopant action at the nanoscale poses a formidable challenge to understanding the elementary mechanisms involved. Here, we perform operando infrared nanoimaging of hydrogen-doped correlated perovskite, neodymium nickel oxide (H-NdNiO3, H-NNO), devices and reveal how an applied field perturbs dopant distribution at the nanoscale. This perturbation leads to stripe phases of varying conductivity perpendicular to the applied field, which define the macroscale electrical characteristics of the devices. Hyperspectral nano-FTIR imaging in conjunction with density functional theory calculations unveils a real-space map of multiple vibrational states of H-NNO associated with OH stretching modes and their dependence on the dopant concentration. Moreover, the localization of excess charges induces an out-of-plane lattice expansion in NNO which was confirmed by in situ X-ray diffraction and creates a strain that acts as a barrier against further diffusion. Our results and the techniques presented here hold great potential for the rapidly growing field of memristors and neuromorphic devices wherein nanoscale ion motion is fundamentally responsible for function