Laboratoire de biophysique experimentale

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Linear Electro-optic Effect in Silicon Nitride Waveguides Enabled by Electric-Field Poling

Camille Sophie Brès, Edgars Nitiss, Anton Stroganov, Boris Zabelich

Stoichiometric silicon nitride (Si3N4) is one of the most mature integrated photonic platforms for linear and nonlinear optical applications on-chip. However, because it is a centrosymmetric material, second-order nonlinear processes are inherently not available in Si3N4, limiting its use for multiple classical and quantum applications. In this work, we implement thermally assisted electric-field poling, which allows charge carrier separation in the waveguide core, leading to a depletion zone formation and the inscription of a strong electric field reaching 20 V/mu m. The latter results in an effective second-order susceptibility (chi((2))) inside the Si3N4 waveguide, making linear electro-optic modulation accessible on the platform for the first time. We develop a numerical model for simulating the poling process inside the waveguide and use it to calculate the diffusion coefficient and the concentration of the charge carriers responsible for the field formation. The charge carrier concentration, as well as the waveguide core size, is found to play a significant role in determining the achievable effective nonlinearity experienced by the optical mode inside the waveguide. Current findings establish a strong groundwork for further advancement of chi((2))-based devices on Si3N4.

AMER CHEMICAL SOC2022

Fluorescent D-Amino Acids for Super-resolution Microscopy of the Bacterial Cell Wall

Juliette Griffie, Suliana Manley, Jiangtao Qiao, Luc Reymond, Ophélie Rutschmann, Faustine Ambroisine Charline Ryckebusch, Willi Leopold Stepp, Chen Zhang

Fluorescent D-amino acids (FDAAs) have previ-ously been developed to enable in situ highlighting of locations of bacterial cell wall growth. Most bacterial cells lie at the edge of the diffraction limit of visible light; thus, resolving the precise details of peptidoglycan (PG) biosynthesis requires super-resolution micros-copy after probe incorporation. Single molecule localization microscopy (SMLM) has stringent requirements on the fluorophore photophysical properties and therefore has remained challenging in this context. Here, we report the synthesis and characterization of new FDAAs compatible with one-step labeling and SMLM imaging. We demonstrate the incorporation of our probes and their utility for visualizing PG at the nanoscale in Gram-negative, Gram-positive, and mycobacteria species. This improved FDAA toolkit will endow researchers with a nanoscale perspective on the spatial distribution of PG biosynthesis for a broad range of bacterial species.

AMER CHEMICAL SOC2022

Event-driven acquisition for content-enriched microscopy

Juliette Griffie, Dora Mahecic, Suliana Manley, Willi Leopold Stepp, Martin Weigert, Chen Zhang

Event-driven acquisition uses neural-network-based recognition of specific biological events to trigger switching between slow and fast super-resolution imaging, enriching the capture of interesting events with high spatiotemporal resolution. A common goal of fluorescence microscopy is to collect data on specific biological events. Yet, the event-specific content that can be collected from a sample is limited, especially for rare or stochastic processes. This is due in part to photobleaching and phototoxicity, which constrain imaging speed and duration. We developed an event-driven acquisition framework, in which neural-network-based recognition of specific biological events triggers real-time control in an instant structured illumination microscope. Our setup adapts acquisitions on-the-fly by switching between a slow imaging rate while detecting the onset of events, and a fast imaging rate during their progression. Thus, we capture mitochondrial and bacterial divisions at imaging rates that match their dynamic timescales, while extending overall imaging durations. Because event-driven acquisition allows the microscope to respond specifically to complex biological events, it acquires data enriched in relevant content.

NATURE PORTFOLIO2022