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Optical antennas for single molecule fluorescence detection at physiological concentration

Deep Punj 1
1 MOSAIC - MOSAIC
FRESNEL - Institut FRESNEL
Abstract : Optical nanoantennas provide a rich control over light at nanoscale to achieve high field enhancement and localization with a large absorption cross-sections. Considering the need for these virtues in broad range of fields the possible applications of these nanoantennas span into the fields of spectroscopy, photovoltaics, single photon sources, biological sensing. This thesis work mainly focuses on characterizing and manipulating optical antenna to detect single molecule fluorescence signal at high concentration of micromolar regime. At such high concentration we need to get the detection volume reduced at least three orders of magnitude beyond diffraction limits. Also the fluorescence signal enhancement is needed to have better value in order to have a single molecule stand out from the background. Chapter 1 deals with the motivation of the thesis by discussing about the well established strategies already applied to tackle the issues of volume reduction and fluorescence rate enhancement and how to go beyond the limitations of these methods. In Chapter 2 we discuss the local surface plasmonic properties of optical nanoantennas responsible for the local field enhancement and give an overview of the applications of optical antennas. Chapter 3 gives the detailed idea of the experimental techniques (Fluorescence Correlation Spectroscopy and Time correlated Single Photon Counting) that have been used to characterize the influence of Optical nanoantenna. Chapter 4 introduces the novel "antenna-in-box" platform, based on a gap-antenna inside a nanoaperture, which combines both enhancement and background screening, offering high single molecule sensitivity at micromolar concentrations. We demonstrate gap-antenna detection volumes of zeptoliter dimensions, corresponding to a 10,000-volume reduction compared to diffraction-limited optics, fluorescence enhancement up to 1100-fold and microsecond transit time. In the last Chapter 5 we show the experimental results on single gold nanoparticles with various diameters giving the idea that with 80 nm gold nanoparticle we can achieve detection volumes down to 270 zeptoliters (three orders of magnitude beyond the diffraction barrier) together with 60-fold enhancement of the fluorescence brightness per molecule. This chapter also includes results on dimers and trimers of 80 nm gold nanoparticles showing light confinement comparable to the "antenna-in-box” platform. The results in this thesis demonstrates the potential of optical antennas, fabricated by top-down ("antenna-in-box” platform) and bottom-up approach (colloidal synthesis of antennas using gold nanoparticles), to confine light and detect single molecule fluorescence at biologically relevant high concentrations regime.
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Deep Punj. Optical antennas for single molecule fluorescence detection at physiological concentration. Optics [physics.optics]. Aix Marseille université, 2014. English. ⟨tel-01119033⟩

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