Institut Fresnel

Abstract Quantitative measurements performed directly in vivo are necessary to understand how forces shape living tissues, yet this remains challenging due to optical scattering and mechanical complexity. Here, we present a method for making absolute force measurements using nanoscopic optical tweezers with a sensitivity of 300 fN in optically turbid biological media. Our approach combines back focal plane interferometry operating within the optical memory effect regime with a global fluctuation-dissipation fitting framework that simultaneously calibrates position detection, trap stiffness, and viscoelastic response. This method overcomes aberration-induced biases by jointly fitting passive fluctuations and driven harmonic responses, enabling robust force reconstruction in thick, scattering tissues within the mechanically relevant frequency range below 300 Hz. We validate our approach using highly scattering Drosophila pupae and embryos, demonstrating reliable in vivo measurements of forces and mechanical properties. Operating at a 1 kHz acquisition bandwidth, the system captures relevant mechanical dynamics without requiring extended high-frequency detection. Using this framework, we quantify the increase in cortical tension during pupal morphogenesis, characterize tissue viscoelasticity, and reveal stage-dependent variations in nuclear membrane tension during embryogenesis, even in the presence of strong ATP-driven fluctuations. Beyond bulk measurements, our method enables the quantitative mechanical characterization of single cells within mechanically coupled tissues.

We present a method for fabricating a self-written waveguide (SWW) between two optical fibers that are single-mode (SM) at 850 nm (780HP/ core diameter: 4.4 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\mu$</tex-math></inline-formula>m). The basic principle consists in exposing an acrylic photopolymer formulation sensitive in the near-infrared range (NIR) to a laser beam transmitted simultaneously from both fibers placed face to face, to build a continuous, flexible and self-aligned optical link. The specificity of the presented process (NIR-SM-SWW) lies in the use of a writing wavelength identical to that intended for single- mode propagation in the fibers. This enables the creation in a single step of a SWW directly adapted to the fundamental mode to be transmitted. A precise pre-positioning stage is used to optimize the process. For best photochemical conditions, a coupling efficiency as high as 82 % (-0.86 dB loss) is demonstrated for a 300 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\mu$</tex-math></inline-formula>m-long link. The effect of fiber-to-fiber axial and lateral distances is also investigated to estimate the propagation loss and misalignment tolerance, respectively. In addition, measurements performed by quantitative phase optical microscopy indicate a homogeneous index profile in the guide. Using these data, optical modeling is performed and compared to experiments, confirming that a high efficiency SM link is actually fabricated, without the need for further fabrication of an external cladding. This method could therefore be easily applied to the SM connection of a SM VCSEL (vertical-cavity surface-emitting laser) to a SM fiber, which is of major interest for the development of compact optical communications and instrumentation systems.

We present a fluorescence diffuse optical tomography reconstruction framework based on the radiative transfer equation. Validated against the diffusion approximation framework, it proves to be a viable alternative for second near-infrared window tomography reconstruction.

This study introduces quantitative photoacoustic imaging to assess intervertebral disc degeneration, characterized by dehydration and associated degenerative diseases, offering a novel approach to evaluate disc health and advance diagnostic techniques.

This paper presents a methodology for constructing a simulated fluorescence tomography database. It details dataset generation, geometry, optical properties, solvers and data processing. The database ensures reproducibility and supports AI applications in biomedical imaging.

Single-molecule orientation and localization microscopy (SMOLM) enables the determination of molecular orientation, wobbling, and position. However, most SMOLM implementations rely on complex point spread function (PSF) fitting, which limits analysis throughput and introduces high computational cost. A way to overcome these limitations is to simplify the analysis using a ratiometric intensity estimation, often relying on polarization projections. While effective in 2D, extending these methods to 3D remains challenging. Here, we introduce a new ratiometric strategy for SMOLM in 3D. Building on the principles of Single Molecule Light Field Microscopy, which captures the 3D position information from a single snapshot by segmenting the back focal plane, we extend this strategy to orientation retrieval. Our approach uses the generalized 3D Stokes formalism to linearly decompose the intensity measurements across the light-field channels, allowing computationally-efficient estimations, while avoiding both complex PSF fitting and polarization projections. This framework, called SMOLM-LFM, enables 6D estimation of single molecules (3D position + 3D orientation) with a simplified optical setup and a large depth-of-field. We present the theoretical foundations, experimental implementation, and validation through measurements on calibration beads, single fluorophores, and cells, thereby demonstrating the method’s potential and practical limitations.

Zero‐mode waveguides (ZMWs) are subwavelength metallic nanoapertures enabling enhanced single‐molecule fluorescence detection at micromolar concentrations in conditions far beyond the diffraction‐limited capabilities of confocal microscopes. However, their widespread use remains limited by the complexity and cost of the nanofabrication techniques, such as focused ion beam and electron‐beam lithography. Here, a scalable, cost‐effective, and high‐throughput method for fabricating high‐performance ZMW arrays is presented, which combining sol‐gel nanoimprint lithography (NIL) with hydrofluoric acid (HF) vapor‐phase etching. This approach enables the parallel fabrication and massive replication of ZMW nanoapertures with attoliter volumes, without requiring expensive equipment. The optical performance of the resulting ZMWs is validated through a series of single‐molecule fluorescence experiments, including burst analysis, fluorescence correlation spectroscopy (FCS), and single‐molecule Förster resonance energy transfer (smFRET). The ZMW nanoapertures demonstrate up to 8× fluorescence brightness enhancement, sub‐millisecond temporal resolution, and broadband spectral operation across the visible range. This method represents a significant advance in making nanophotonic devices more accessible, paving the way for a broader adoption of ZMWs in single‐molecule biosensing and integrated nanophotonic systems.

Accessing molecular orientation in single molecule localization microscopy (SMLM) offers valuable insights into molecular ordering and organization in biological structures. Conventional single-molecule orientation-localization microscopy (SMOLM) methods typically rely on either engineering the point-spread function (PSF) of the microscope to encode the orientation information or on polarization resolved detection. While PSF engineering enables detailed orientation analysis, it often requires complex computational analysis and suffers from reduced performance in dense cellular environments due to PSF spreading and overlap. In contrast, polarization-based approaches are easier to implement and are more fit when imaging dense samples but are unable to retrieve the axial information of single molecules. To overcome this limitation, we introduce the Polarization MultiFocus Microscope (PolMFM), a novel method for simultaneously retrieving the orientation and 3D position of single molecules. PolMFM combines the orientation measurement capabilities of a 4-polarization splitting scheme with a 3-planes multifocus microscope (MFM) enabling the reconstruction of molecular 2D orientation, wobble, and axial localization in a single acquisition. Through simulations, we demonstrate that PolMFM accurately recovers both orientation and 3D position, despite PSF defocusing. Experimental validation with reference samples shows that PolMFM matches the orientation precision of 4-Polar STORM, while uniquely adding axial information. We demonstrate the power of PolMFM by resolving the orientation and 3D positions of molecules in actin filaments in fixed cells, and by revealing that chromatin in crickets undergoes major reorganization and increased ordering during spermiogenesis. These findings highlight the potential of PolMFM for high-precision, multidimensional super-resolution imaging in complex and crowded biological environments.

Periodontal disease (PD) and cognitive disorders (CDs) are common in older people, and these variables appear to be linked. The aim of this article was to assess this association using an umbrella meta-analysis. PubMed and MEDLINE were searched for records until June 2025. The groups were compared using odds ratio (OR) and relative risk (RR). A total of 20 meta-analyses were included. Individuals with PD and its consequences had higher chances of having/developing all-type CDs: periodontitis (OR = 1.65, 95% CI: 1.37-1.97, p = < 0.0001), tooth loss (OR = 1.51, 95% CI: 1.32-1.71, p = < 0.0001). The risk was much higher for patients with severe periodontitis: (OR = 2.69, 95% CI: 2.26-3.20, p = < 0.0001). Pooled analysis for cohort studies was (RR = 1.26, 95% CI: 1.20-1.32, p = < 0.0001). PD is associated with CDs with low to moderate certainty of evidence measured by GRADE.