Spontaneous emission control with planar and corrugated dielectric structures for ultrasensitive fluorescence analysis in the life sciences

Summary form only. The past decade has seen the breakthrough of ultrasensitive fluorescence analysis in the life sciences. The advent of highly efficient single photon counting avalanche photodiodes and the use of confocal fluorescent microscopes have opened the way to very high signal-to-background ratios, raising single-molecule detection to the rank of routine technique. Several methods of data processing such as fluorescence correlation spectroscopy (FCS) or burst integrated fluorescence lifetime (BIFL) have shown the tremendous potential of those techniques to study diffusion processes in cell membranes, protein conformational changes, or ligand-target interactions. In all cases, high numerical aperture microscope objectives were needed to collect about 30% of the total emitted light (1.2 NA). In this context, we discuss the ability of electromagnetic structures such as microcavities or resonant waveguide gratings to go beyond this value by exerting spontaneous emission control on biological fluorophores, and hence by condensing the emitted light in particular directions. We present theoretical and experimental results obtained with Cyanine 5 molecules studied in an FCS setup which show the interest of planar dielectric multilayer structures to enhance the measured count rate per molecule, and their potential to simplify the design of single-molecule detection experiments.