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We demonstrate the application of a microfluidic platform combining spatiotemporal oxygen control and long-term microscopy monitoring to observe tumour spheroid response to hypoxia. The platform is capable of recreating physiologically-relevant low and cycling oxygen levels not attainable in traditional cell culture environments, while image-based monitoring visualizes cell response to these physiologically-relevant conditions. Monitoring spheroid cultures during hypoxic exposure allows us to observe, for the first time, that spheroids swell and shrink in response to time-varying oxygen profiles switching between 0% and 10% O2; this swelling-shrinkage behaviour appears to be driven by swelling of individual cells within the spheroids. We also apply the system to monitoring tumour models during anticancer treatment under varying oxygen conditions. We observe higher uptake of the anticancer agent doxorubicin under a cycling hypoxia profile than under either chronic hypoxia or in vitro normoxia, and the two-photon microscopy monitoring facilitated by our system also allows us to observe heterogeneity in doxorubicin uptake within spheroids at the single-cell level. Combining optical sectioning microscopy with precise spatiotemporal oxygen control and 3D culture opens the door for a wide range of future studies on microenvironmental mechanisms driving cancer progression and resistance to anticancer therapy. These types of studies could facilitate future improvements in cancer diagnostics and treatment.

Immobilization of live micro-organisms on solid substrates is an important prerequisite for atomic force microscopy (AFM) bio-experiments. The method employed must immobilize the cells firmly enough to enable them to withstand the lateral friction forces exerted by the tip during scanning but without denaturing the cell interface. In this work, a generic method for the assembly of living cells on specific areas of substrates is proposed. It consists in assembling the living cells within the patterns of microstructured, functionalized poly-dimethylsiloxane (PDMS) stamps using convective/capillary deposition. This versatile approach is validated by applying it to two systems of foremost importance in biotechnology and medicine: Saccharomyces cerevisiae yeasts and Aspergillus fumigatus fungal spores. We show that this method allows multiplexing AFM nanomechanical measurements by force spectroscopy on S. cerevisiae yeasts and high-resolution AFM imaging of germinated Aspergillus conidia in buffer medium. These two examples clearly demonstrate the immense potential of micro-organism assembly on functionalized, microstructured PDMS stamps by convective/capillary deposition for performing rigorous AFM bio-experiments on living cells.

Several optical surface sensing techniques, such as Surface Plasmon Resonance (SPR), work by imaging the base of a prism by one of its faces. However, such a fundamental optical concern has not been fully analyzed and understood so far, and spatial resolution remains a critical and controversial issue. In SPR, the propagation length L(x) of the surface plasmon waves has been considered as the limiting factor. Here, we demonstrate that for unoptimized systems geometrical aberrations caused by the prism can be more limiting than the propagation length. By combining line-scan imaging mode with optimized prisms, we access the ultimate lateral resolution which is diffraction-limited by the object light diffusion. We describe several optimized configurations in water and discuss the trade-off between L(x) and sensitivity. The improvement of resolution is confirmed by imaging micro-structured PDMS stamps and individual living eukaryote cells and bacteria on field-of-view from 0.1 to 20 mm(2).

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Silicon photonics can address a variety of applications, from datacom and biosensing to lidars. Recently, this technology has been explored for gas sensing. Detection and identification of odors remains a critical challenge in diverse areas such as air quality, food spoilage, or personal well-being. In this work, we present an olfactory sensor based on an array of 64 biofunctionalized Mach-Zehnder interferometers integrated on a silicon nitride platform. The ability to analyze odors at ppm level is demonstrated for several volatile organic compounds.

This work proposes a miniaturized system able to perform multiple cell capture followed by cell-type selective release from a biochip surface. Unlabelled lymphocytes were first specifically captured onto a DNA array by antibody-DNA conjugates. The immobilized cells were subsequently released under spatiotemporal control within local heating generated by intense Surface Plasmon Resonance (SPR) produced by laser illumination.