Cristaux photoniques pour des applications en microscopie de fluorescence

In recent years, many research activities were devoted to both enhancing the emission of fluorescent molecules and improving the resolution of conventional far field microscopy. Increasing the intrinsic fluorescence of molecules is of great practical interest because it enhances the potentiality of molecular-fluorescence-based devices and techniques, whereas the reduction in the detection volume enables the observation of events (e.g. in living cells) at the single molecule level.

In this context, methods based on wavelength-scale periodic dielectric structures, such as Photonic Crystals (PhCs), are very attractive since modes can be engineered to achieve high spatial and spectral light confinement. In particular, the resulting narrow optical resonances are largely exploited for sensing (e.g. label-free) applications. Our activity focuses on fluorescence confinement using silicon nitride (SiN) PhCs as substrates for fluorescence microscopy.

We have recently shown an easy-to-implement scheme with both axial and lateral confinement as well as fluorescence enhancement based on resonant excitation of 2D-PhC slow modes under normal incidence. A 65 fold enhancement in the excitation was achieved in the near field region (100 nm deep and 1 µm wide) of the resonant mode. This, together with the high spatial resolution, makes our device an excellent substrate for fluorescence microscopies, allowing the observation of localized events in cell membranes with reduced background noise.

Figure 1 : (a) Dielectric photonic crystal slab with a water drop on top, illuminated by a tightly focused Gaussian beam in the visible. (b) SEM image of the fabricated SiN-PhC.		Figure 1 : Sketch of the excitation setup using a confocal microscope. The excitation light is focused onto the PhC. The focal spot is imaged onto the detector via a pinhole. DM: dichroic mirror, M: mirror, L: lens, PH: pinhole, F: filter, PMT: photomultiplier. Transmission (b) and fluorescence (c) confocal images recorded simultaneously by raster scanning a solution of 1.5 M R6G/water over the PhC. The emission of molecules is enhanced due to the resonant excitation.

Contact : Alejandro Yacomotti, Ariel Levenson et Sophie Bouchoule (Action de recherche Cristaux et circuits photoniques non-linéaires agiles )

Références : L. C. Estrada, O.E. Martinez, M. Brunstein, S. Bouchoule, L. Le Gratiet, A. Talneau, I. Sagnes, P. Monnier, J. A. Levenson, A. Yacomotti, Optics Express 18, 3693 (2010)