Andrea Steinbrück

Bio: Andrea Steinbrück is an academic researcher from Los Alamos National Laboratory. The author has contributed to research in topics: Nanoparticle & Surface plasmon resonance. The author has an hindex of 14, co-authored 26 publications receiving 1275 citations.

Two types of luminescence blinking revealed by spectroelectrochemistry of single quantum dots

Abstract: Photoluminescence blinking—random switching between states of high (ON) and low (OFF) emissivities—is a universal property of molecular emitters found in dyes1, polymers2, biological molecules3 and artificial nanostructures such as nanocrystal quantum dots, carbon nanotubes and nanowires4, 5, 6. For the past 15 years, colloidal nanocrystals have been used as a model system to study this phenomenon5, 6. The occurrence of OFF periods in nanocrystal emission has been commonly attributed to the presence of an additional charge7, which leads to photoluminescence quenching by non-radiative recombination (the Auger mechanism)8. However, this ‘charging’ model was recently challenged in several reports9, 10. Here we report time-resolved photoluminescence studies of individual nanocrystal quantum dots performed while electrochemically controlling the degree of their charging, with the goal of clarifying the role of charging in blinking. We find that two distinct types of blinking are possible: conventional (A-type) blinking due to charging and discharging of the nanocrystal core, in which lower photoluminescence intensities correlate with shorter photoluminescence lifetimes; and a second sort (B-type), in which large changes in the emission intensity are not accompanied by significant changes in emission dynamics. We attribute B-type blinking to charge fluctuations in the electron-accepting surface sites. When unoccupied, these sites intercept ‘hot’ electrons before they relax into emitting core states. Both blinking mechanisms can be electrochemically controlled and completely suppressed by application of an appropriate potential.

Lifetime blinking in nonblinking nanocrystal quantum dots

Abstract: Nanocrystal quantum dots are attractive materials for applications as nanoscale light sources. One impediment to these applications is fluctuations of single-dot emission intensity, known as blinking. Recent progress in colloidal synthesis has produced nonblinking nanocrystals; however, the physics underlying blinking suppression remains unclear. Here we find that ultra-thick-shell CdSe/CdS nanocrystals can exhibit pronounced fluctuations in the emission lifetimes (lifetime blinking), despite stable nonblinking emission intensity. We demonstrate that lifetime variations are due to switching between the neutral and negatively charged state of the nanocrystal. Negative charging results in faster radiative decay but does not appreciably change the overall emission intensity because of suppressed nonradiative Auger recombination for negative trions. The Auger process involving excitation of a hole (positive trion pathway) remains efficient and is responsible for charging with excess electrons, which occurs via Auger-assisted ionization of biexcitons accompanied by ejection of holes.

Comprehensive analysis of the effects of CdSe quantum dot size, surface charge, and functionalization on primary human lung cells.

Abstract: The growing potential of quantum dots (QDs) in applications as diverse as biomedicine and energy has provoked much dialogue about their conceivable impact on human health and the environment at large. Consequently, there has been an urgent need to understand their interaction with biological systems. Parameters such as size, composition, surface charge, and functionalization can be modified in ways to either enhance biocompatibility or reduce their deleterious effects. In the current study, we simultaneously compared the impact of size, charge, and functionalization alone or in combination on biological responses using primary normal human bronchial epithelial cells. Using a suite of cellular end points and gene expression analysis, we determined the biological impact of each of these properties. Our results suggest that positively charged QDs are significantly more cytotoxic compared to negative QDs. Furthermore, while QDs functionalized with long ligands were found to be more cytotoxic than those functi...

Sensoric potential of gold–silver core–shell nanoparticles

Abstract: The sensitivities of five different core–shell nanostructures were investigated towards changes in the refractive index of the surrounding medium. The shift of the localized surface plasmon resonance (LSPR) maximum served as a measure of the (respective) sensitivity. Thus, gold–silver core–shell nanoparticles (NPs) were prepared with different shell thicknesses in a two-step chemical process without the use of any (possibly disturbing) surfactants. The measurements were supported by ultramicroscopic images in order to size the resulting core–shell structures. When compared to sensitivities of nanostructures reported in the literature with those of the (roughly spherical) gold–silver core–shell NPs, the latter showed comparable (or even higher) sensitivities than gold nanorods. The experimental finding is supported by theoretical calculation of optical properties of such core–shell NP. Extinction spectra of ideal spherical and deformed core–shell NPs with various core/shell sizes were calculated, and the presence of an optimal silver shell thickness with increased sensitivity was confirmed. This effect is explained by the existence of two overlapping plasmon bands in the NP, which change their relative intensity upon change of refractive index. Results of this research show a possibility of improving LSPR sensor by adding an extra metallic layer of certain thickness.

Functionalization-Dependent Induction of Cellular Survival Pathways by CdSe Quantum Dots in Primary Normal Human Bronchial Epithelial Cells

Abstract: Quantum dots (QDs) are semiconductor nanocrystals exhibiting unique optical properties that can be exploited for many practical applications ranging from photovoltaics to biomedical imaging and drug delivery. A significant number of studies have alluded to the cytotoxic potential of these materials, implicating Cd-leaching as the causal factor. Here, we investigated the role of heavy metals in biological responses and the potential of CdSe-induced genotoxicity. Our results indicate that, while negatively charged QDs are relatively noncytotoxic compared to positively charged QDs, the same does not hold true for their genotoxic potential. Keeping QD core composition and size constant, 3 nm CdSe QD cores were functionalized with mercaptopropionic acid (MPA) or cysteamine (CYST), resulting in negatively or positively charged surfaces, respectively. CYST-QDs were found to induce significant cytotoxicity accompanied by DNA strand breakage. However, MPA-QDs, even in the absence of cytotoxicity and reactive oxyge...

Nanostructured plasmonic sensors.

Abstract: Surface plasmons (SPs) are coherent oscillations of conduction electrons on a metal surface excited by electromagnetic radiation at a metal -dielectric interface. The growing field of research on such light -metal interactions is known as ‘plasmonics’. 1-3 This branch of research has attracted much attention due to its potential applications in miniaturized optical devices, sensors, and photonic circuits as well as in medical diagnostics and therapeutics. 4-8

Hybrid passivated colloidal quantum dot solids

Abstract: Improved performance in a photovoltaic device made of colloidal quantum dots is achieved through a combination of passivation by halide anions and organic crosslinking.

Organic Optoelectronic Materials: Mechanisms and Applications

Abstract: Organic (opto)electronic materials have received considerable attention due to their applications in thin-film-transistors, light-emitting diodes, solar cells, sensors, photorefractive devices, and many others. The technological promises include low cost of these materials and the possibility of their room-temperature deposition from solution on large-area and/or flexible substrates. The article reviews the current understanding of the physical mechanisms that determine the (opto)electronic properties of high-performance organic materials. The focus of the review is on photoinduced processes and on electronic properties important for optoelectronic applications relying on charge carrier photogeneration. Additionally, it highlights the capabilities of various experimental techniques for characterization of these materials, summarizes top-of-the-line device performance, and outlines recent trends in the further development of the field. The properties of materials based both on small molecules and on conjug...

Quantum dots: bright and versatile in vitro and in vivo fluorescence imaging biosensors

Abstract: Semiconductor quantum dots (QDs) have become important fluorescent probes for in vitro and in vivo bioimaging research. Their nanoparticle surfaces for versatile bioconjugation, their adaptable photophysical properties for multiplexed detection, and their superior stability for longer investigation times are the main advantages of QDs compared to other fluorescence imaging agents. Here, we review the recent literature dealing with the design and application of QD-bioconjugates for advanced in vitro and in vivo imaging. After a short summary of QD preparation and their most important properties, different QD-based imaging applications will be discussed from the technological and the biological point of view, ranging from super-resolution microscopy and single-particle tracking over in vitro cell and tissue imaging to in vivo investigations. A substantial part of the review will focus on multifunctional applications, in which the QD fluorescence is combined with drug or gene delivery towards theranostic approaches or with complementary technologies for multimodal imaging. We also briefly discuss QD toxicity issues and give a short outlook on future directions of QD-based bioimaging.