Distance Dependence of Single-Fluorophore Quenching by Gold Nanoparticles Studied on DNA Origami
ABSTRACT 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.
SourceAvailable from: Anirban Samanta[Show abstract] [Hide abstract]
ABSTRACT: DNA nanotechnology has touched the epitome of miniaturization by integrating various nanometer size particles with nanometer precision. This enticing bottom-up approach has employed small DNA tiles, large multi-dimensional polymeric structures or more recently DNA origami to organize nanoparticles of different inorganic materials, small organic molecules or macro-biomolecules like proteins, and RNAs into fascinating patterns that are difficult to achieve by other conventional methods. Here, we are especially interested in the self-assembly of nanomaterials that are potentially attractive elements in the burgeoning field of nanophotonics. These materials include plasmonic nanoparticles, quantum dots, fluorescent organic dyes, etc. DNA based self-assembly allows excellent control over distance, orientation and stoichiometry of these nano-elements that helps to engineer intelligent systems that can potentially pave the path for future technology. Many outstanding structures have been fabricated that are capable of fine tuning optical properties, such as fluorescence intensity and lifetime modulation, enhancement of Raman scattering and emergence of circular dichroism responses. Within the limited scope of this review we have tried to give a glimpse of the development of this still nascent but highly promising field to its current status as well as the existing challenges before us.Nanoscale 01/2015; 7(6). DOI:10.1039/c4nr06283c · 6.74 Impact Factor
[Show abstract] [Hide abstract]
ABSTRACT: Background Molecular sensing/imaging utilizing fluorophores has been one of the most frequently used techniques in biomedical research. As for any molecular imaging techniques, fluorescence mediated sensing always seeks for greater specificity and sensitivity. Since fluorophores emit fluorescence while their electron energy state changes, manipulating the local electromagnetic field around the fluorophores may be a way to enhance the specificity and sensitivity. Gold nanoparticles (GNPs) are known to form a very strong electromagnetic field on their surface [i.e., surface plasmon field (SPF)], upon receiving photonic energy. The level of fluorescence change by GNP-SPF may range from complete quenching to extensive enhancement, depending upon the SPF strength, excitation and emission wavelengths, and quantum yield of the fluorophore.Method Here, we report a novel design that utilizes BOTH fluorescence quenching and enhancement abilities of the GNP in one single nano-entity, providing high specificity and sensitivity. The construct utilizes a specially designed molecular dual-spacer that places the fluorphore at the location with an appropriate GNP-SFP strength before and after exposed to the biomarker. A model system to test the concept was an optical signal mediator activated by urokinase-type plasminogen activator (uPA; breast cancer secreting enzyme).ResultsThe resulting contrast agent showed less than 10% of the natural fluorescence but, in the presence of uPA, the fluorescence emission is triggered and emits its fluorescence approximately twice of the natural form.Conclusion This study demonstrated that our novel design of an optical contrast agent can be conditionally activated with enhanced sensitivity, using both quenching and enhancement phenomena of fluorophores in the electromagnetic field of the appropriate strengths (in this case, locally generated by the GNP-SPF) This entity is similar to molecular beacon in terms of specificity but with greater sensitivity. In addition, it is not restricted to only DNA or RNA sensing but for any designs that cause the change in the distance between the fluorophore and GNP, upon the time of encountering biomarker of interest.Journal of Nanobiotechnology 12/2014; 12(1):56. DOI:10.1186/s12951-014-0056-2 · 4.08 Impact Factor
[Show abstract] [Hide abstract]
ABSTRACT: The effect of saturable absorption in a dye decreases significantly in the presence of functionalized hydrogen-induced exfoliated wrinkled graphene (f-HEG). The absorption spectra give strong evidence of complex formation in the ground state. The fluorescence spectra and nonlinear optical properties of the dye are affected by f-HEG and silver decorated graphene (Ag-f-HEG) by various degrees. The open aperture Z-scan and degenerate four wave mixing (DFWM) techniques have been used to record the drastic changes in the nonlinear optical parameters of dye in presence of f-HEG and Ag-f-HEG. The results indicate a reduction in the average value of the nonlinearity due to formation of the non-fluorescent ground-state charge-transfer complex. At high input irradiance the optical limiting capability of the dye-f-HEG system has been found to be enhanced. The pre-existing charge transfer between silver nanoparticles and f-HEG reduces the strength of dye-f-HEG complex formation.Journal of Photochemistry and Photobiology A Chemistry 11/2014; DOI:10.1016/j.jphotochem.2014.11.010 · 2.29 Impact Factor