Paul Kim

Comparison study of gold nanohexapods, nanorods, and nanocages for photothermal cancer treatment.

Gold nanohexapods represent a novel class of optically tunable nanostructures consisting of an octahedral core and six arms grown on its vertices. By controlling the length of the arms, their localized surface plasmon resonance peaks could be tuned from the visible to the near-infrared region for deep penetration of light into soft tissues. Herein we compare the in vitro and in vivo capabilities of Au nanohexapods as photothermal transducers for theranostic applications by benchmarking against those of Au nanorods and nanocages. While all these Au nanostructures could absorb and convert near-infrared light into heat, Au nanohexapods exhibited the highest cellular uptake and the lowest cytotoxicity in vitro for both the as-prepared and PEGylated nanostructures. In vivo pharmacokinetic studies showed that the PEGylated Au nanohexapods had significant blood circulation and tumor accumulation in a mouse breast cancer model. Following photothermal treatment, substantial heat was produced in situ and the tumor metabolism was greatly reduced for all these Au nanostructures, as determined with (18)F-flourodeoxyglucose positron emission tomography/computed tomography ((18)F-FDG PET/CT). Combined together, we can conclude that Au nanohexapods are promising candidates for cancer theranostics in terms of both photothermal destruction and contrast-enhanced diagnosis.

Protein‐Protected Au Clusters as a New Class of Nanoscale Biosensor for Label‐Free Fluorescence Detection of Proteases

Proteases are a major class of enzymes that catalyze the hydrolysis of peptide bonds to break down proteins into smaller pieces in a process known as proteolysis.[1] Ubiquitous in nature, proteases are present in all living cells and organisms, and are known to play a pivotal role in the development and control of many biological processes.[2] The importance of proteases is also manifested by a large number of pathological conditions that involve alteration of protease levels, including cancer, arthritis, as well as neurodegenerative and cardiovascular diseases.[3]

High Efficiency Tandem Thin-Perovskite/Polymer Solar Cells with a Graded Recombination Layer.

Perovskite-containing tandem solar cells are attracting attention for their potential to achieve high efficiencies. We demonstrate a series connection of a ∼ 90 nm thick perovskite front subcell and a ∼ 100 nm thick polymer:fullerene blend back subcell that benefits from an efficient graded recombination layer containing a zwitterionic fullerene, silver (Ag), and molybdenum trioxide (MoO3). This methodology eliminates the adverse effects of thermal annealing or chemical treatment that occurs during perovskite fabrication on polymer-based front subcells. The record tandem perovskite/polymer solar cell efficiency of 16.0%, with low hysteresis, is 75% greater than that of the corresponding ∼ 90 nm thick perovskite single-junction device and 65% greater than that of the polymer single-junction device. The high efficiency of this hybrid tandem device, achieved using only a ∼ 90 nm thick perovskite layer, provides an opportunity to substantially reduce the lead content in the device, while maintaining the high performance derived from perovskites.

Enhanced Hemangioblast Generation and Improved Vascular Repair and Regeneration from Embryonic Stem Cells by Defined Transcription Factors

Summary The fetal liver kinase 1 (FLK-1)+ hemangioblast can generate hematopoietic, endothelial, and smooth muscle cells (SMCs). ER71/ETV2, GATA2, and SCL form a core transcriptional network in hemangioblast development. Transient coexpression of these three factors during mesoderm formation stage in mouse embryonic stem cells (ESCs) robustly enhanced hemangioblast generation by activating bone morphogenetic protein (BMP) and FLK-1 signaling while inhibiting phosphatidylinositol 3-kinase, WNT signaling, and cardiac output. Moreover, etsrp, gata2, and scl inhibition converted hematopoietic field of the zebrafish anterior lateral plate mesoderm to cardiac. FLK-1+ hemangioblasts generated by transient coexpression of the three factors (ER71-GATA2-SCL [EGS]-induced FLK-1+) effectively produced hematopoietic, endothelial, and SMCs in culture and in vivo. Importantly, EGS-induced FLK-1+ hemangioblasts, when codelivered with mesenchymal stem cells as spheroids, were protected from apoptosis and generated functional endothelial cells and SMCs in ischemic mouse hindlimbs, resulting in improved blood perfusion and limb salvage. ESC-derived, EGS-induced FLK-1+ hemangioblasts could provide an attractive cell source for future hematopoietic and vascular repair and regeneration.

Visualizing the Dynamics of Nanoparticles in Liquids by Scanning Electron Microscopy.

Taking advantage of ionic liquid nonvolatility, the Brownian motions of nanospheres and nanorods in free-standing liquid films were visualized in situ by scanning electron microscopy. Despite the imaging environments high vacuum, a liquid cell was not needed. For suspensions that are dilute and films that are thick compared to the particle diameter, the translational and rotational diffusion coefficients determined by single-particle tracking agree with theoretical predictions. In thinner films, a striking dynamical pairing of nanospheres was observed, manifesting a balance of capillary and hydrodynamic interactions, the latter strongly accentuated by the two-dimensional film geometry. Nanospheres at high concentration displayed subdiffusive caged motion. Concentrated nanorods in the thinner films transiently assembled into finite stacks but did not achieve high tetratic order. The illustrated imaging protocol will broadly apply to the study of soft matter structure and dynamics with great potential impact.

Chemical and Morphological Control of Interfacial Self-Doping for Efficient Organic Electronics

Solution-based processing of materials for electrical doping of organic semiconductor interfaces is attractive for boosting the efficiency of organic electronic devices with multilayer structures. To simplify this process, self-doping perylene diimide (PDI)-based ionene polymers are synthesized, in which the semiconductor PDI components are embedded together with electrolyte dopants in the polymer backbone. Functionality contained within the PDI monomers suppresses their aggregation, affording self-doping interlayers with controllable thickness when processed from solution into organic photovoltaic devices (OPVs). Optimal results for interfacial self-doping lead to increased power conversion efficiencies (PCEs) of the fullerene-based OPVs, from 2.62% to 10.64%, and of the nonfullerene-based OPVs, from 3.34% to 10.59%. These PDI-ionene interlayers enable chemical and morphological control of interfacial doping and conductivity, demonstrating that the conductive channels are crucial for charge transport in doped organic semiconductor films. Using these novel interlayers with efficient doping and high conductivity, both fullerene- and nonfullerene-based OPVs are achieved with PCEs exceeding 9% over interlayer thicknesses ranging from ≈3 to 40 nm.

Transition in Dynamics as Nanoparticles Jam at the Liquid/Liquid Interface

Nanoparticles (NPs) segregated to the liquid/liquid interface form disordered or liquid-like assemblies that show diffusive motions in the plane of the interface. As the areal density of NPs at the interface increases, the available interfacial area decreases, and the interfacial dynamics of the NP assemblies change when the NPs jam. Dynamics associated with jamming was investigated by X-ray photon correlation spectroscopy. Water-in-toluene emulsions, formed by a self-emulsification at the liquid/liquid interface and stabilized by ligand-capped CdSe-ZnS NPs, provided a simple, yet powerful platform, to investigate NP dynamics. In contrast to a single planar interface, these emulsions increased the number of NPs in the incident beam and decreased the absorption of X-rays in comparison to the same path length in pure water. A transition from diffusive to confined dynamics was manifested by intermittent dynamics, indicating a transition from a liquid-like to a jammed state.

Orthogonally Aligned Block Copolymer Line Patterns on Minimal Topographic Patterns

We demonstrate the generation of block copolymer (BCP) line patterns oriented orthogonal to a very small (minimal) topographic trench pattern over arbitrarily large areas using solvent-vapor annealing. Increasing the thickness of BCP films induced an orthogonal alignment of the BCP cylindrical microdomains, where full orthogonal alignment of the cylindrical microdomains with respect to the trench direction was obtained at a film thickness corresponding to 1.70 L0. A capillary flow of the solvent across the trenches was a critical factor in the alignment of the cylindrical microdomains. Grazing incidence small-angle X-ray scattering was used to determine the orientation function of the microdomains, with a value of 0.997 being found reflecting a nearly perfect orientation. This approach to produce orthogonally aligned BCP line patterns could be extended to the nanomanufacturing and fabrication of hierarchical nanostructures.

Refractive Index Tuning of Hybrid Materials for Highly Transmissive Luminescent Lanthanide Particle–Polymer Composites

High-refractive-index ZrO2 nanoparticles were used to tailor the refractive index of a polymer matrix to match that of luminescent lanthanide-ion-doped (La0.92Yb0.075Er0.005F3) light-emitting particles, thereby reducing scattering losses to yield highly transparent emissive composites. Photopolymerization of blends of an amine-modified poly(ether acrylate) oligomer and tailored quantities of ZrO2 nanoparticles yielded optically transparent composites with tailored refractive indices between 1.49 and 1.69. By matching the refractive index of the matrix to that of La0.92Yb0.075Er0.005F3, composites with high transmittance (>85%) and low haze from the visible to infrared regions, bright 1530 nm optical emissions were achieved at solids loadings of La0.92Yb0.075Er0.005F3, ranging from 5 to 30 vol %. These optical results suggest that a hybrid matrix approach is a versatile strategy for the fabrication of functional luminescent optical composites of high transparency.

Thickness mapping of freestanding Ionic Liquid films using Electron Energy Loss Spectroscopy in the TEM

One of the biggest challenges in Electron Microscopy in fluids is to overcoming the limitation of the high vacuum requirements. To observe the dynamics of fluid samples, sophisticated fluid cells have been developed that typically use 25 nm Silicon Nitride membranes with a separation of ~ 200 nm [1]. Recently it was demonstrated that graphene can be used to trap liquids for TEM observation [2] which improves resolution substantially due to the negligible scattering contribution of the graphene layers. However, sample sizes are quite small, ~ 100 nm in diameter.