Visualization of Lipid Raft Membrane Compartmentalization in Living RN46A Neuronal Cells Using Single Quantum Dot Tracking

Lipid rafts are cholesterol-enriched subdomains in the plasma membrane that have been reported to act as a platform to facilitate neuronal signaling; however, they are suspected to have a very short lifetime, up to only a few seconds, which calls into question their roles in biological signaling. To better understand their diffusion dynamics and membrane compartmentalization, we labeled lipid raft constituent ganglioside GM1 with single quantum dots through the connection of cholera toxin B subunit, a protein that binds specifically to GM1. Diffusion measurements revealed that single quantum dot-labeled GM1 ganglioside complexes undergo slow, confined lateral diffusion with a diffusion coefficient of ∼7.87 × 10^–2 μm²/s and a confinement domain about 200 nm in size. Further analysis of their trajectories showed lateral confinement persisting on the order of tens of seconds, comparable to the time scales of the majority of cellular signaling and biological reactions. Hence, our results provide further evidence in support of the putative function of lipid rafts as signaling platforms

Synthesis of Ultrasmall and Magic-Sized CdSe Nanocrystals

Nanocrystals exhibit useful properties not found in their bulk counterparts; however, a subclass of nanocrystals that consist of diameters on the order of 2 nm or less further exhibit unique properties. As synthetic methodologies of nanocrystals have matured, greater emphasis has been made on controlling the early stages of the reaction in order to gain access to these sub-2 nm species. This review provides an overview of ultrasmall and magic-sized nanocrystals, and the diverse chemical means to obtain them. Due to their small size and their resultant properties, these ultrasmall and magic-sized nanocrystals have a distinct advantage in many applications including achieving renal clearance for the purpose of biological imaging, producing simple and high-quality white LEDs, and controlling the growth of nanocrystals to produce various morphologies

Synthesis of Ultrasmall and Magic-Sized CdSe Nanocrystals

Nanocrystals exhibit useful properties not found in their bulk counterparts; however, a subclass of nanocrystals that consist of diameters on the order of 2 nm or less further exhibit unique properties. As synthetic methodologies of nanocrystals have matured, greater emphasis has been made on controlling the early stages of the reaction in order to gain access to these sub-2 nm species. This review provides an overview of ultrasmall and magic-sized nanocrystals, and the diverse chemical means to obtain them. Due to their small size and their resultant properties, these ultrasmall and magic-sized nanocrystals have a distinct advantage in many applications including achieving renal clearance for the purpose of biological imaging, producing simple and high-quality white LEDs, and controlling the growth of nanocrystals to produce various morphologies

Novel Synthesis of Chalcopyrite Cu_<i>x</i>In_<i>y</i>S₂ Quantum Dots with Tunable Localized Surface Plasmon Resonances

The burgeoning field of thin film quantum dot photovoltaics has made considerable strides toward efficient and inexpensive forms of third generation solar cells. However, these technologies have largely been based upon toxic metal-containing materials, limiting their foreseeable applications. Here we present a synthesis of nontoxic and stable Cu_<i>x</i>In_<i>y</i>S₂ quantum dots with tunable size and band gap. Interestingly, this synthesis leads to the presence of a broad-band and size-dependent absorption peak in the infrared (IR), attributed to localized surface plasmon resonances (LSPRs). Due to the sensitivity of their LSPR peak to quantum dot size and solvent refractive index, these quantum dots provide an attractive candidate for tunable plasmon resonance applications. And, if these LSPRs are found to be coupled with excitonic transitions, they may result in sizable increases in photovoltaic efficiency

The Possibility and Implications of Dynamic Nanoparticle Surfaces

Understanding the precise nature of a surface or interface is a key component toward optimizing the desired properties and function of a material. For semiconductor nanocrystals, the surface has been shown to modulate fluorescence efficiency, lifetime, and intermittency. The theoretical picture of a nanocrystal surface has included the existence of an undefined mixture of trap states that arise from incomplete passivation. However, our recent scanning transmission electron microscope movies and supporting theoretical evidence suggest that, under excitation, the surface is fluctuating, creating a dynamic population of surface and subsurface states. This possibility challenges our fundamental understanding of the surface and could have far-reaching ramifications for nanoparticle-based technologies. In this Perspective, we discuss the current theories behind the optical properties of nanocrystals in the context of fluxionality

Elimination of Hole–Surface Overlap in Graded CdS_<i>x</i>Se_1–<i>x</i> Nanocrystals Revealed by Ultrafast Fluorescence Upconversion Spectroscopy

Interaction of charge carriers with the surface of semiconductor nanocrystals plays an integral role in determining the ultimate fate of the excited state. The surface contains a dynamic ensemble of trap states that can localize excited charges, preventing radiative recombination and reducing fluorescence quantum yields. Here we report quasi-type-II band alignment in graded alloy CdS_<i>x</i>Se_1–<i>x</i> nanocrystals revealed by femtosecond fluorescence upconversion spectroscopy. Graded alloy CdS_<i>x</i>Se_1–<i>x</i> quantum dots are a compositionally inhomogeneous nano-heterostructure designed to decouple the exciton from the nanocrystal surface. The large valence band offset between the CdSe-rich core and CdS-rich shell separates the excited hole from the surface by confining it to the core of the nanocrystal. The small conduction band offset, however, allows the electron to delocalize throughout the entire nanocrystal and maintain overlap with the surface. Indeed, the ultrafast charge carrier dynamics reveal that the fast 1–3 ps hole-trapping process is fully eliminated with increasing sulfur composition and the decay constant for electron trapping (∼20–25 ps) shows a slight increase. These findings demonstrate progress toward highly efficient nanocrystal fluorophores that are independent of their surface chemistry to ultimately enable their incorporation into a diverse range of applications without experiencing adverse effects arising from dissimilar environments

Ferroelectric Particles Generated through a Simple, Room-Temperature Treatment of CdSe Quantum Dots

Ferroelectric Particles Generated through a Simple, Room-Temperature Treatment of CdSe Quantum Dot

Ferroelectric Particles Generated through a Simple, Room-Temperature Treatment of CdSe Quantum Dots

Ferroelectric Particles Generated through a Simple, Room-Temperature Treatment of CdSe Quantum Dot

Direct Electronic Property Imaging of a Nanocrystal-Based Photovoltaic Device by Electron Beam-Induced Current via Scanning Electron Microscopy

Scanning electron microscopy (SEM) electron beam-induced current (EBIC) studies were performed on the cross-section of a nanocrystal-based hybrid bulk heterojunction photovoltaic device. Using these techniques, the short circuit carrier collection efficiencies are mapped with a better than 100 nm resolution. Electronically deficient and proficient regions within the photoactive layer are determined. The results show that only a fraction of the CdSe nanorod:P3HT layer (P3HT = poly-3­(hexylthiophene)) at the Al cathode interface shows primary collection of charged carriers, in which the photoactivity decreases exponentially away from the interface. The recombination losses of the photoactive layer away from this interface prove that the limiting factor of the device is the inability for electrons to percolate between nanoparticles; to alleviate this problem, an interparticle network that conducts the electrons from one nanorod to the next must be established. Furthermore, the EBIC technique applied to the nanocrystalline device used in this study is the first measurement of its kind and can be applied toward other similar architectures

Plasmonic Cu_<i>x</i>In_<i>y</i>S₂ Quantum Dots Make Better Photovoltaics Than Their Nonplasmonic Counterparts

A synthetic approach has recently been developed which results in Cu_<i>x</i>In_<i>y</i>S₂ quantum dots (QDs) possessing localized surface plasmon resonance (LSPR) modes in the near-infrared (NIR) frequencies. In this study, we investigate the potential benefits of near-field plasmonic effects centered upon light absorbing nanoparticles in a photovoltaic system by developing and verifying nonplasmonic counterparts as an experimental control. Simple QD-sensitized solar cells (QD-SSCs) were assembled which show an 11.5% relative increase in incident photon conversion efficiency (IPCE) achieved in the plasmon-enhanced devices. We attribute this increase in IPCE to augmented charge excitation stemming from near-field “antenna” effects in the plasmonic Cu_<i>x</i>In_<i>y</i>S₂ QD-SSCs. This study represents the first of its kind; direct interrogation of the influence of plasmon-on-semiconductor architectures with respect to excitonic absorption in photovoltaic systems