We study the distance-dependent quenching of fluorescence due to a metallic nanoparticle in proximity of a fluorophore. In our single-molecule measurements, we achieve excellent control over structure and stoichiometry by using self-assembled DNA structures (DNA origami) as a breadboard where both the fluorophore and the 10 nm metallic nanoparticle are positioned with nanometer precision. The single-molecule spectroscopy method employed here reports on the co-localization of particle and dye, while fluorescence lifetime imaging is used to directly obtain the correlation of intensity and fluorescence lifetime for varying particle to dye distances. Our data can be well explained by exact calculations that include dipole-dipole orientation and distances. Fitting with a more practical model for nanosurface energy transfer yields 10.4 nm as the characteristic distance of 50% energy transfer. The use of DNA nanotechnology together with minimal sample usage by attaching the particles to the DNA origami directly on the microscope coverslip paves the way for more complex experiments exploiting dye-nanoparticle interactions.
"Most impressively, a five-fold overall enhancement of upconversion emission was demonstrated in NaYF4: Yb3+, Er3+ nanocrystals when coupled them with gold island films 17. However, all previously reported enhancement factors were less than 5-fold, and in many cases, quenching was unavoidable 18, 19, mainly due to the following reasons: (1) frequency mismatching between the localized plasmon resonance (usually determined by the used metal, their shape, size, the dielectric environment, and the spacer distance) and the used emission/excitation light, (2) a competition of a few processes including a increase of the excitation rate by the local field enhancement (LFE) 20, an enhancement of radiative decay rate by the surface plasmon-coupled emission (SPCE) and quenching that reduces the efficiency caused by the non-radiative energy transferring (NRET) from the upconversion material to the metal surfaces 21,22, all of which will be greatly dependent on the spacing distance between the upconversion material and the metal 23-26. "
[Show abstract][Hide abstract] ABSTRACT: We report a localized surface plasmon enhanced upconversion luminescence in Au/SiO2/Y2O3:Yb(3+),Er(3+) nanoparticles when excited at 980 nm. By adjusting the silica spacer's thickness, a maximum 9.59-fold enhancement of the green emission was obtained. Effect of the spacer distance on the Au-Y2O3:Yb(3+), Er(3+) green upconversion mechanism was numerically simulated and experimentally demonstrated. In theory for radiative decay and excitation rates, they can be largely enhanced at the spacer thicknesses of less than 70 and 75 nm, respectively, and the quenching can be caused by the non-radiative energy transferring at the distance of less than 55 nm.
"The efficiency of quenching of fluorescence and fluorescence lifetime of the donor in the presence of AuNPs depends very much on the size of the nanoparticles as well as the distance of separation of the fluorophore from it. To have a control on the latter, people have adopted techniques like tagging DNA type spacers of definite lengths (tunable spacers)     , sheathing the AuNPs by variable number of monomolecular films , etc. Singlemolecule spectroscopy has also been exploited to explore and understand the mechanism of AuNP induced quenching   . Although increase in the fluorescence is observed with smaller AuNPs (≤10 nm) which is rationalized from an enhanced local field induced by the nanoparticle , for larger nanoparticles (≥10 nm) quenching always dominates. "
[Show abstract][Hide abstract] ABSTRACT: Superquenching of the laser dye, coumarin 153 (C153), by 16–59 nm gold nanoparticles (AuNPs) is reported from the steady state and time-resolved fluorometric investigations. Quenching of the steady state fluorescence of C153 and its fluorescence lifetime reveals energy transfer from the probe to AuNP in the photoexcited state. The Stern–Volmer constants (KSV, 107–109 mol−1 dm3) determined from the quenching of the donor lifetime in the presence of AuNPs of varying sizes are orders of magnitude higher than those for the normal photochemical quenching processes. The quenching efficiency increases with an increase in the size of the nanoparticles. The importance of the work lies in providing a new and simple system to be exploited for developing biosensor with high degree of sensitivity.
Journal of Photochemistry and Photobiology A Chemistry 08/2012; 242:44–50. DOI:10.1016/j.jphotochem.2012.05.027 · 2.50 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: We report a gold nanoparticle (AuNP)-based fluorescence quenching system via metal coordination for the simple assay of protease activity. Carboxy AuNPs (5 nm in core diameter) functioned as both quenchers and metal chelators without requiring further modification with multidentate ligands; therefore, they were strongly associated with the hexahistidine regions of dye-tethered peptides in the presence of Ni(II) ions, leading to notable fluorescence quenching over the varying molar ratios of dye to AuNP. Upon the addition of matrix metalloproteinase-7 (MMP-7), the fluorescent intensity was efficiently recovered in one-pot mixture especially at 10:1–100:1 molar ratios of dye to AuNP. Consequently, the dequenching degree was dependent on the MMP-7 concentration in a hyperbolic manner, ranging from as low as 10 to 1,000 ng mL−1. In this regard, we anticipate that the developed system will give us a general way to construct nanoparticle–dye conjugates and will find applications in the analyses of many other proteases mediating significant biological processes with low background and high sensitivity.
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