arXiv subjects

Benjamin Flavel

Publications and source records attributed to Benjamin Flavel.

4 recordsLinked to original sources

arXiv2026

Two Photon excitation microscopy of individual Single-Walled Carbon Nanotubes

Two-photon fluorescence imaging achieves deep-tissue penetration through long excitation wavelengths and nonlinear excitation confinement. The 1700 nm transparency window is particularly attractive, as it optimally balances tissue scattering and absorption. However, efficient fluorophores for two-photon excitation in this window remain limited. Moreover the weak near-infrared emission of individual emitters, and the low photon detection efficiency, has so far precluded single-particle imaging. Here, we characterize the two-photon excitation properties of chirality-sorted pristine and quantum color center-functionalized single-walled carbon nanotubes under 1700 nm excitation. By measuring and comparing their two-photon action cross-sections, we identify quantum color center-functionalized (6,5) nanotubes emitting at 1140 nm, as the most promising emitter, with an exceptionally large cross-section of (57 \pm 2).103 GM. Leveraging these favorable photophysical properties, we image individual nanotubes under 1700 nm excitation, to our knowledge the first demonstration of single-particle imaging at this wavelength. These results establish quantum color center-functionalized (6,5) nanotube as a strong candidate for long-wavelength two-photon imaging and lay the groundwork for deep-tissue single-particle imaging.

physics.optics↗

arXiv2026

Resolving Scale-Dependent Diffusivity in the Brain Extracellular Space

Transport through the brain extracellular space has traditionally been summarized by effective diffusion coefficients measured over specific observation ranges. Whether local mobility remains predictive as the same molecule explores larger distances remains unresolved. Here, we track individual ultrashort carbon nanotubes in three dimensions within living hippocampal tissue, following their motion from nanometre to micrometre scales. Using freely diffusing nanotubes in water as an experimental reference, we resolve trajectory-specific crossover lengths beyond which instantaneous diffusivity decreases, with slice-level medians of 0.67 $\mu$m in the pyramidal layer and 0.52 $\mu$m in the radiatum. The pyramidal layer combines higher short-time diffusivity with an approximately twofold larger post-crossover restriction exponent than the radiatum ($\vartheta$ = 0.77 versus 0.38). This decoupling of local mobility from larger-scale exploration is incompatible with a scale-independent rescaling of transport, showing that effective extracellular diffusivity must be interpreted relative to the scale of exploration.

physics.bio-ph↗

arXiv2024

Hyperspectral near infrared imaging using a tunable spectral phasor

Hyperspectral imaging captures both spectral and spatial information from a sample. The near infrared (NIR, > 800 nm) is advantageous for biomedical imaging as it falls into the tissue transparency window but also contains vibrational overtone and combination modes useful for molecular fingerprinting. Here, we demonstrate hyperspectral NIR imaging using a spectral phasor transformation (HyperNIR). This method employs a liquid crystal variable retarder (LCVR) for tunable, wavelength-dependent sine-, cosine and no filtering that transforms optical signals into phasor space. Spectral information is thus obtained with just three images. The LCVR can be adjusted to cover a spectral range from 900 nm to 1600 nm in windows tunable from 50 nm to 700 nm. This approach enables distinguishing NIR fluorophores with emission peaks less than 5 nm apart. Furthermore, we demonstrate label-free hyperspectral NIR reflectance imaging to identify plastic polymers and to monitor in vivo plant health. The approach uses the full camera resolution and reaches hyperspectral frame rates of 0.2 per second, limited only by the switching rate of the LCVR. HyperNIR facilitates straightforward hyperspectral imaging with standard NIR cameras for applications in biomedical imaging and environmental monitoring.

physics.optics↗

arXiv2021

Moir\'e-induced Vibrational Coupling in Double Walled Carbon Nanotubes

Moir\'e patterns are additional, long-range periodicities in twisted crystalline bilayers. They are known to fundamentally change the electronic states of the layers, but similar effects on their mechanical and vibrational properties have not been discussed so far. Here we show that the Moir\'e potential shifts the radial breathing mode in double walled carbon nanotubes (DWCNTs). The change of frequency is expected to be proportional to the shift in optical transition energies, which are induced by the Moir\'e patterns. To verify our model we performed resonant Raman scattering on purified and sorted semiconducting DWCNTs. We find that the radial breathing mode shifts up to 14 cm$^{-1}$ higher in energy followed by optical transitions energies displacement up to 200 meV to lower energies, compared to the single-walled tubes. We show how to identify the strong coupling condition in DWCNTs from their phonon frequencies and construct a Kataura plot to aid their future experimental assignment.

cond-mat.mes-hall↗