Giant Suppression of Photobleaching for Single Molecule Detection via the Purcell Effect

Abstract

ABSTRACT:We report giant suppression of photobleaching and a prolonged lifespan of single fluorescent molecules via the Purcell effect in plasmonic nanostructures. The plasmonic structures enhance the spontaneous emission of excited fluorescent molecules, reduce the probability of activating photochemical reactions that destroy the molecules, and hence suppress the bleaching. Experimentally, we observe up to a 1000-fold increase in the total number of photons that we can harvest from a single fluorescent molecule before it bleaches. This approach demonstrates the potential of using the Purcell effect to manipulate photochemical reactions at the subwavelength scale. KEYWORDS: Nano-optics, single-molecule fluorescence spectroscopy, plasmonics P hotobleaching is a photochemical reaction of fluorescent molecules that irreversibly destroys their fluorescence capability. It determines the lifespan of a single fluorescent molecule and imposes a fundamental limit on the total number of photons that can be harvested from the molecule. 1,2 Considerable efforts have been devoted to suppressing photobleaching, which culminates primarily in chemical-based strategies that aim to make the local environment more chemically inert to fluorophores, 3,4 or modifying the structures and energy landscapes of fluorophores to be more resistant to photobleaching. 5,6 Progress has been achieved along these routes, including the discovery of oxygen scavenger systems, 3 photostable green fluorescent proteins, 5 and semiconductor quantum dots. 7 However, the increasing demand for more photons from a single molecule 1,8 requires new strategies beyond these chemical approaches.Recent progress in plasmonics manifests a "physical" approach to address the challenge. Plasmonics 9−11 offer a new way to mediate the interaction between a molecule and its local electromagnetic environment. 12,13 The surface plasmon of metallic nanostructures allows for deep subwavelength confinement of light 14,15 and enhancement of the local density of optical states. 16,17 These structures can substantially enhance the spontaneous emission of fluorophores near the metal surface, that is, the so-called Purcell enhancement. 18−20 In contrast to photonic crystals, 21−24 the plasmonic Purcell enhancement is broadband. The impacts of the plasmonic Purcell enhancement on photostability have been noticed previously. For instance, Hale et al. have observed reduction of photo-oxidation of semiconducting polymer when doped with silica core-gold nanoshells, 25 and Muthu et al. and Malicka et al. have observed decreasing photobleaching of fluoresce dyes on the surface of thin silver films 26 and silver nanoparticles. 27 Recently, the Purcell effect has been further expanded to tune the spectroscopic properties of dye molecules to selectively remove a long-lived triplet state, 28 enhance the fluorescence signal, 29 suppress quantum dot blinking, 30 and manipulate selection rules. 31 A novel core−shell type of plasmonic nanocomposite structures has also been developed as nanoc...

Plasmon‐Enhanced Photocurrent of Photosynthetic Pigment Proteins on Nanoporous Silver

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Tamm plasmon- and surface plasmon-coupled emission from hybrid plasmonic–photonic structures

“…As a result, the metallic structures can convert the usual omnidirectional emission into directional emission and can modify the polarization of the coupled emission without the use of any lenses or polarizers [7–9]. The near-field coupling also results in spectral control on emission [10], enhanced spontaneous emission rates of molecules [11], giant suppression of photobleaching for single-molecule detection [12], and a strong fluorescence enhancement [13–15]. Due to these significant advantages of near-field coupled emission, it is of great importance to investigate the factors affecting the near-field coupling interactions between fluorophores and plasmonic fields.…”

Nanoantenna enhanced emission of light-harvesting complex 2: the role of resonance, polarization, and radiative and non-radiative rates

“…As the fluorophore spends less time in the excited state, the photostability will increase and thus a higher number of photons can be detected before irreversible photobleaching occurs. 27,28 To date only a few studies on emission enhancement of lightharvesting complexes have been reported using chemically synthesized metal nanostructures such as silver island films, 29,30 gold, [31][32][33] and silver nanoparticles. 34 In most studies the individual contributions of excitation and QY changes to the total fluorescence enhancement have not been disentangled.…”