44 research outputs found
Infrared-spectroscopic, dynamic near-field microscopy of living cells and nanoparticles in water
Infrared fingerprint spectra can reveal the chemical nature of materials down to 20-nm detail, far below the diffraction limit, when probed by scattering-type scanning near-field optical microscopy (s-SNOM). But this was impossible with living cells or aqueous processes as in corrosion, due to water-related absorption and tip contamination. Here, we demonstrate infrared s-SNOM of water-suspended objects by probing them through a 10-nm thick SiN membrane. This separator stretches freely over up to 250~µm, providing an upper, stable surface to the scanning tip, while its lower surface is in contact with the liquid and localises adhering objects. We present its proof-of-principle applicability in biology by observing simply drop-casted, living E. coli in nutrient medium, as well as living A549 cancer cells, as they divide, move and develop rich sub-cellular morphology and adhesion patterns, at 150~nm resolution. Their infrared spectra reveal the local abundances of water, proteins, and lipids within a depth of ca. 100~nm below the SiN membrane, as we verify by analysing well-defined, suspended polymer spheres and through model calculations. SiN-membrane based s-SNOM thus establishes a novel tool of live cell nano-imaging that returns structure, dynamics and chemical composition. This method should benefit the nanoscale analysis of any aqueous system, from physics to medicine
Nanoscale mechanical manipulation of ultrathin SiN membranes enabling infrared near-field microscopy of liquid-immersed samples
Scattering scanning near-field optical microscopy (s-SNOM) is a powerful
technique for mid-infrared spectroscopy at nanometer length scales. By
investigating objects in aqueous environments through ultrathin membranes,
s-SNOM has recently been extended towards label-free nanoscopy of the dynamics
of living cells and nanoparticles, assessing both the optical and the
mechanical interactions between the tip, the membrane and the liquid suspension
underneath. Here, we report that the tapping AFM tip induces a reversible
nanometric deformation of the membrane manifested as either an indentation or
protrusion. This mechanism depends on the driving force of the tapping
cantilever, which we exploit to minimize topographical deformations of the
membrane to improve optical measurements. Furthermore, we show that the tapping
phase, or phase delay between driving signal and tip oscillation, is a highly
sensitive observable for quantifying the mechanics of adhering objects,
exhibiting highest contrast for low tapping amplitudes where the membrane
remains nearly flat. We correlate mechanical responses with simultaneously
recorded spectroscopy data to reveal the thickness of nanometric water pockets
between membrane and adhering objects. Besides a general applicability of depth
profiling, our technique holds great promise for studying mechano-active
biopolymers and living cells, biomaterials that exhibit complex behaviors when
under a mechanical load.Comment: 31 pages, 7 figures, 7 supplementary figure
Mid-infrared frequency comb spanning an octave based on an Er fiber laser and difference-frequency generation
We describe a coherent mid-infrared continuum source with 700 cm-1 usable
bandwidth, readily tuned within 600 - 2500 cm-1 (4 - 17 \mum) and thus covering
much of the infrared "fingerprint" molecular vibration region. It is based on
nonlinear frequency conversion in GaSe using a compact commercial 100-fs-pulsed
Er fiber laser system providing two amplified near-infrared beams, one of them
broadened by a nonlinear optical fiber. The resulting collimated mid-infrared
continuum beam of 1 mW quasi-cw power represents a coherent infrared frequency
comb with zero carrier-envelope phase, containing about 500,000 modes that are
exact multiples of the pulse repetition rate of 40 MHz. The beam's
diffraction-limited performance enables long-distance spectroscopic probing as
well as maximal focusability for classical and ultraresolving near-field
microscopies. Applications are foreseen also in studies of transient chemical
phenomena even at ultrafast pump-probe scale, and in high-resolution gas
spectroscopy for e.g. breath analysis.Comment: 8 pages, 2 figures revised version, added reference
Anisotropic Strain Induced Soliton Movement Changes Stacking Order and Bandstructure of Graphene Multilayers
The crystal structure of solid-state matter greatly affects its electronic
properties. For example in multilayer graphene, precise knowledge of the
lateral layer arrangement is crucial, since the most stable configurations,
Bernal and rhombohedral stacking, exhibit very different electronic properties.
Nevertheless, both stacking orders can coexist within one flake, separated by a
strain soliton that can host topologically protected states. Clearly, accessing
the transport properties of the two stackings and the soliton is of high
interest. However, the stacking orders can transform into one another and
therefore, the seemingly trivial question how reliable electrical contact can
be made to either stacking order can a priori not be answered easily. Here, we
show that manufacturing metal contacts to multilayer graphene can move solitons
by several m, unidirectionally enlarging Bernal domains due to arising
mechanical strain. Furthermore, we also find that during dry transfer of
multilayer graphene onto hexagonal Boron Nitride, such a transformation can
happen. Using density functional theory modeling, we corroborate that
anisotropic deformations of the multilayer graphene lattice decrease the
rhombohedral stacking stability. Finally, we have devised systematics to avoid
soliton movement, and how to reliably realize contacts to both stacking
configurations
Transient infrared nanoscopy resolves the millisecond photoswitching dynamics of single lipid vesicles in water
Understanding the biophysical and biochemical properties of molecular
nanocarriers under physiological conditions and with minimal interference is
crucial for advancing nanomedicine, photopharmacology, drug delivery,
nanotheranostics and synthetic biology. Yet, analytical methods struggle to
combine precise chemical imaging and measurements without perturbative
labeling. This challenge is exemplified for azobenzene-based photoswitchable
lipids, which are intriguing reagents for controlling nanocarrier properties on
fast timescales, enabling, e.g., precise light-induced drug release processes.
Here, we leverage the chemical recognition and high spatio-temporal resolution
of scattering-type scanning near-field optical microscopy (s-SNOM) to
demonstrate non-destructive, label-free mid-infrared (MIR) imaging and
spectroscopy of photoswitchable liposomes below the diffraction limit and the
tracking of their dynamics down to 50 ms resolution. The vesicles are adsorbed
on an ultrathin 10-nm SiN membrane, which separates the sample space from the
tip space for stable and hour-long observations. By implementing a transient
nanoscopy approach, we accurately resolve, for the first time, photoinduced
changes in both the shape and the MIR spectral signature of individual vesicles
and reveal abrupt change dynamics of the underlying photoisomerization process.
Our findings highlight the methods potential for future studies on the complex
dynamics of unlabeled nanoscale soft matter, as well as, in a broader context,
for host-guest systems, energy materials or drugs.Comment: 4 figures, 10 supplementary figure
Nanoscale infrared spectroscopy as a non-destructive probe of extraterrestrial samples
Advances in the spatial resolution of modern analytical techniques have tremendously augmented the scientific insight gained from the analysis of natural samples. Yet, while techniques for the elemental and structural characterization of samples have achieved sub-nanometre spatial resolution, infrared spectral mapping of geochemical samples at vibrational 'fingerprint' wavelengths has remained restricted to spatial scales >10 mu m. Nevertheless, infrared spectroscopy remains an invaluable contactless probe of chemical structure, details of which offer clues to the formation history of minerals. Here we report on the successful implementation of infrared near-field imaging, spectroscopy and analysis techniques capable of sub-micron scale mineral identification within natural samples, including a chondrule from the Murchison meteorite and a cometary dust grain (Iris) from NASA's Stardust mission. Complementary to scanning electron microscopy, energy-dispersive X-ray spectroscopy and transmission electron microscopy probes, this work evidences a similarity between chondritic and cometary materials, and inaugurates a new era of infrared nano-spectroscopy applied to small and invaluable extraterrestrial samples
Nanoscale infrared spectroscopy as a non-destructive probe of extraterrestrial samples
Advances in the spatial resolution of modern analytical techniques have tremendously augmented the scientific insight gained from the analysis of natural samples. Yet, while techniques for the elemental and structural characterization of samples have achieved sub-nanometre spatial resolution, infrared spectral mapping of geochemical samples at vibrational 'fingerprint' wavelengths has remained restricted to spatial scales >10 mu m. Nevertheless, infrared spectroscopy remains an invaluable contactless probe of chemical structure, details of which offer clues to the formation history of minerals. Here we report on the successful implementation of infrared near-field imaging, spectroscopy and analysis techniques capable of sub-micron scale mineral identification within natural samples, including a chondrule from the Murchison meteorite and a cometary dust grain (Iris) from NASA's Stardust mission. Complementary to scanning electron microscopy, energy-dispersive X-ray spectroscopy and transmission electron microscopy probes, this work evidences a similarity between chondritic and cometary materials, and inaugurates a new era of infrared nano-spectroscopy applied to small and invaluable extraterrestrial samples
All-electronic terahertz nanoscopy
Probing conductivity in a contactless way with nanoscale resolution is a pressing demand in such active fields as quantum materials, superconductivity, and molecular electronics. Here, we demonstrate a laser-and cryogen-free microwave-technology-based scattering-type scanning near-field optical microscope powered by an easily aligned free-space beam with a tunable frequency up to 0.75 THz. It uses Schottky diode components to record background-free amplitude and phase nano-images, for the first time in the terahertz range, which is uniquely sensitive for assessing conduction phenomena. Images of Si with doped nanostructures prove a conductance sensitivity corresponding to 10(16) cm(-3) mobile carriers, at 50 nm spatial resolution