Medical optical imaging | EPFL Graph Search

Medical optical imaging is the use of light as an investigational imaging technique for medical applications, pioneered by American Physical Chemist Britton Chance. Examples include optical microscopy, spectroscopy, endoscopy, scanning laser ophthalmoscopy, laser Doppler imaging, and optical coherence tomography. Because light is an electromagnetic wave, similar phenomena occur in X-rays, microwaves, and radio waves. Optical imaging systems may be divided into diffusive and ballistic imaging systems. A model for photon migration in turbid biological media has been developed by Bonner et al. Such a model can be applied for interpretation data obtained from laser Doppler blood-flow monitors and for designing protocols for therapeutic excitation of tissue chromophores. Diffusive optical imaging Diffuse optical imaging (DOI) is a method of imaging using near-infrared spectroscopy (NIRS) or fluorescence-based methods. When used to create 3D volumetric m

Photoresponsive Nanocarriers Based on Lithium Niobate Nanoparticles for Harmonic Imaging and On-Demand Release of Anticancer Chemotherapeutics

Luigi Bonacina, Dario Diviani, Sandrine Gerber, Adrian Stefan Gheata, Simon Kaiser, Jérémy Vuilleumier

Nanoparticle-based drug delivery systems have the potential for increasing the efficiency of chemotherapeutics by enhancing the drug accumulation at specific target sites, therebyreducing adverse side effects and mitigating patient acquired resistance. In particular, photo-responsive nanomaterials have attracted much interest due to their ability to release molecularcargos on demand upon light irradiation. In some settings, they can also provide complementary information by optical imaging on the (sub)cellular scale. We herein present a system based on lithium niobate harmonic nanoparticles (LNO HNPs) for the decoupled multi-harmonic cell imaging and near-infrared light-triggered delivery of an erlotinib derivative (ELA) for the treatment of epidermal growth factor receptor (EGFR)-overexpressing carcinomas. The ELA cargo was covalently conjugated to the surface of silica-coated LNO HNPs through a coumarinyl photo-cleavable linker, achieving a surface loading of the active molecule of 27 nmol/mg NPs. The resulting nanoconjugates (LNO-CM-ELA NPs) were successfully imaged upon pulsed laser excitation at 1250 nm in EGFR-overexpressing human prostate cancer cells DU145 by detecting the second harmonic emission at 625 nm, in the tissue transparency window. Tuning the laser at 790 nm resulted in the uncaging of the ELA cargo as a result of the second harmonic emission of the inorganic HNP core at 395 nm. This protocol induced a significant growth inhibition in DU145 cells, which was only observed upon specific irradiation at 790 nm, highlighting the promising capabilities of LNO-CM-ELA NPs for theranostic applications.

2022

Investigation of the Electromechanical Properties of Graphene

Mohamed Malik Benameur

This thesis studies the optical and electro-mechanical properties of novel atomically thin crystals. It deals with the carbon based material, graphene, and with layered transition metal dichalcogenides with the common formula MX2. The first part describes a new optical model for detecting ultra-thin, two dimensional nanocrystals under optical microscope. A simple optical model is used to calculate the contrast of nanolayers on SiO2. The model is extended for imaging using the green channel of a video camera. Atomic force microscopy combined with optical imaging confirms that single layers of graphene, MoS2, WSe2 and NbSe2 are detectable on 90 nm and 270 nm SiO2. The optical contrast of multi-layer nanocrystals is also reported and allows easy differentiation between single, double and triple layers. Optical imaging is proposed as a rapid, non invasive and low cost method for the detection of ultra-thin nanocrystals. The second part is devoted to studying the electromechanical properties of mono-layer and bilayer graphene. The interplay between the mechanical and the electrical properties of graphene nanoribbons is probed by nanoindentation techniques based on AFM. Deflection of monolayer graphene nanoribbons with widths ranging between 60 nm and 300 nm results in a linear increase in their electrical resistance. The sensitivity of the response increases for nar- rower ribbons and variations of the resistance up to 15% are measured. The electromechanical response of bilayer graphene shows a superposition of a linear response with oscillations of the electrical resistance. We present possible scenarios to explain the origin of these oscillations.

EPFL2012

Physics of optically driven nanojunctions

Philippe Andreas Rölli

Recent years have seen spectacular developments in the domain of nano-optics. Alongside the well-known techniques of super-resolution microscopy progress in nanofabrication has enabled important improvements in the fields of optical imaging and spectroscopy. Nowadays enhancements of specific near-field interactions by nano-antennae/cavities allows the optical readout of single molecule properties in a number of different systems. The observation of normal modes of vibration for example carries essential information on the orientation, link to the interface and environment in which the molecule is embedded. This thesis develops firstly a novel theoretical frame for these vibration-cavity interactions by following the optomechanical formalism, which has proven to be an accurate treatment of a wide variety of mechanical systems interacting with a laser field. By leveraging this framework, we investigate on the one hand several quantum limits. On the other hand, for the parameter space experimentally available and for well-designed cavities, novel regimes of interaction between the collective mode of vibration of an ensemble of molecules and an optical tone seem within reach. In parallel, this thesis experimentally explores one specific realization of such a system. In collaboration with the group of Christophe Galland we constructed the optical setups necessary to interrogate our nanostructures. The class of structures constructed, known as self-assembled nanojunctions or nanoparticles on mirror, reaches confinement of electric fields via plasmonic modes close to its fundamental limit and enables the study of many different mechanical systems whose thickness consist in a single molecule. Along this research we have developed techniques to characterize mechanical, electronic and thermal observables of nanojunctions interacting with an optical field. Our experimental study has enabled the discovery of a novel effect related to the electronic confinement of these quasi-0-dimensional structures. The characteristic photoluminescence of metallic nanostructures is found to consistently blink in nanojunctions akin to other quantum emitters. The mechanisms explaining in detail this blinking remain debatable but the numerous experimental data collected highlight the key role of the interface in the specificities of the blinking observed. This finding opens novel ways to characterize the important and to date ill-described question of the interfaces in nanojunctions. The observed modifications of the nanojunctions optical properties might constitute an interesting step towards the development of a novel class of functional materials ('gap-materials') with enhanced and tailored electro-optical properties. The last part of this thesis considers one technological application for this class of material by conceptually developing a new kind of detector based on the upconversion of an infrared photon to the visible; exploiting thus in a unique way the optical properties of the molecular system. The study of the quantum noises of these detectors highlights two exciting and technologically relevant directions for such devices : at room temperature these systems operate with levels of noise below state of the art devices, at lower temperatures these systems open an unexplored path towards single photon detection in a spectral range where this technology remains unavailable to date.

EPFL2020

Physics of optically driven nanojunctions

Philippe Andreas Rölli

EPFL2020