Mid-infrared photothermal microscopy has demonstrated unique capabilities in the field of chemical imaging including sub-diffraction limited resolution and sub cellular imaging. Vibrational Infrared Photothermal and Phase Signal (VIPPS) introduces an additional contrast mechanism based on different thermal properties. This enables high contrast imaging of features with overlapping absorption profiles but different thermal diffusion characteristics. Our approach paves the way for high contrast sub-diffraction limited imaging of secondary protein conformations in fibroblast cells grown in a protein rich collagen matrix at the subcellular level.
X-ray Free-Electron Lasers (XFELs) offer a unique opportunity to study the structural dynamics of proteins on a
femtosecond time-scale. To realize the full potential of XFEL sources for studying time-resolved biomolecular
processes however, requires the optimization and development of devices that can both act as a trigger and a
delivery mechanism for the system of interest. Here we present numerical simulations and actual devices exploring
the conditions required for the development of successful mixing and injection devices for tracking the molecular
dynamics of proteins in solution on micro to nanosecond timescales using XFELs. The mechanism for combining
reagents employs a threefold combination of pico-liter volumes, lamination and serpentine mixing. Focusing and
delivering the sample in solution is achieved using the Gas Dynamic Virtual Nozzle (GDVN), which was specifically
developed to produce a micrometer diameter, in-vacuum liquid jet. We explore the influence of parameters such as
flow rate and gas pressure on the mixing time and jet stability, and explore the formation of rapid homogeneously
mixed jets for ‘mix-and-inject’ liquid scattering experiments at Synchrotron and XFEL facilities.
KEYWORDS: Plasmonics, Biological and chemical sensing, Polarization, Metals, Refractive index, Visible radiation, Chemical analysis, Microfluidics, Eye, Water
Plasmonic devices provide a unique sensitivity to changes in the permittivity of the immediate, near-surface environment. In this work we explore the use of dual pitch plasmonic devices combined with microfluidics for polarization enhanced colour sensing of a chemicals’ refractive index. We demonstrate that the use of cross-shaped apertures can produce polarization tunable color based sensing in the optical regime and show that the spectral variations as a function of the incident polarization can be decomposed into contributions from the two orthogonal modes that characterize the dual pitch plasmonic device. Finally we demonstrate that the use of the full colour spectrum in the visible range in combination with polarization control enables sensing ‘by-eye’ of refractive index changes below 1 × 10-3 RIU.
Nanofabrication of metamaterials based on thin metallic films have resulted in a host of different designs that support Extraordinary Optical Transmission (EOT). In contrast to the more widely studied circular-shaped apertures, cross-shaped apertures have characteristics which can be modified in response to linearly polarized light, opening up new pathways for light manipulation at the nanoscale. Here we present a systematic study of the influence of device geometry and composition on the functional characteristics of polarisation controlled optical plasmonic devices. We also discuss some issues that arise using the focused ion beam (FIB) milling technique to fabricate optical metamaterials. In particular, we show that producing high-quality patterns lead to a significant over-deposition of the substrate material. This effect significantly alters the metal surface chemistry, which poses a considerable obstacle for applications involving molecular and bio sensing. This work lays the foundation for the optimisation of the properties of optical plasmonic devices for a wide-range of applications including colour filtering and bio-sensing.
Engineered materials with feature sizes on the order of a few nanometres offer the potential for producing metamaterials with properties which may differ significantly from their bulk counterpart. Here we describe the production of plasmonic colour filters using periodic arrays of nanoscale cross shaped apertures fabricated in optically opaque silver films. Due to its relatively low loss in the visible and near infrared range, silver is a popular choice for plasmonic devices, however it is also unstable in wet or even ambient conditions. Here we show that ultra-thin layers of Diamond-Like Carbon (DLC) can be used to prevent degradation due to oxidative stress, ageing and corrosion. We demonstrate that DLC effectively protects the sub-micron features which make up the plasmonic colour filter under both atmospheric conditions and accelerated aging using iodine gas. Through a systematic study we confirm that the nanometre thick DLC layers have no effect on the device functionality or performance.
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