Jiwon Bang

Surface engineering of inorganic nanoparticles for imaging and therapy

Many kinds of inorganic nanoparticles (NPs) including semiconductor, metal, metal oxide, and lanthanide-doped NPs have been developed for imaging and therapy applications. Their unique optical, magnetic, and electronic properties can be tailored by controlling the composition, size, shape, and structure. Interaction of such NPs with cells and/or in vivo compartments is critically determined by the surface properties, and sophisticated control over the NP surface is essential to control their fate in biological environments. We review NP surface coating strategies using the categories of small surface ligand, polymer, and lipid. Use of small ligand molecules has the advantage of maintaining the minimal hydrodynamic (HD) size. Polymers can be advantageous in NP anchoring by combining multiple affinity groups. Encapsulation of NPs in polymers, lipids or surfactants can preserve the as-synthesized NPs. NP surface properties and reaction conditions should be carefully considered to obtain a bioconjugate that maintains the physicochemical properties of NP and functionalities of the conjugated biomolecules. We highlight how the surface properties of NPs impact their interactions with cells and in vivo compartments, especially focused on the important surface design parameters such as HD size, surface charge, and targeting. Typically, maximal cellular uptake can take place in the intermediate NP size range of 40-60nm. Clearance of NPs from blood circulation is largely dependent on the degree of uptake by reticuloendothelial system when they are larger than 10nm. When the HD size is below 10nm, NPs show broad distribution over many organs. Reduction of HD size below the limit of renal barrier can achieve fast clearance of NPs. For maximal tumor accumulation, NPs should have long blood circulation time and should be large enough to prevent rapid penetration. NPs are also desired to rapidly clear out from the body after the mission before they cause toxic side effects. However, efficient clearance from the body to avoid side effects may result in the reduction in residence time required for accumulation in target tissues. Smart design of NP surface coating that can meet the conflicting demands can open a new avenue of NP applications. Surface charge and hydrophobicity need to be carefully considered for NP surface design. Positively charged NPs more adsorb on cell membranes and consequently show higher level of internalizations when compared with negatively charged or neutral NPs. NPs encounter a large variety of biomolecules in vivo, where non-specific adsorptions can potentially alter the physicochemical properties of the NPs. For optimal performance, NPs are suggested to have neutral surface charge at physiological conditions, small HD size, and minimal non-specific adsorption levels. Zwitterionic NP surface coating by small surface ligands can be a promising approach. Toxicity is one of most critical issues, where proper control of the NP surface can significantly reduce the toxicities.

One-Pot Fabrication of High-Quality InP/ZnS (Core/Shell) Quantum Dots and Their Application to Cellular Imaging

True colors: High-quality InP and InP/ZnS quantum dots (QDs) are obtained by means of a simple one-pot method in the presence of polyethylene glycol (PEG). Rapid and size-controlled reactions lead to highly crystalline and nearly monodisperse QDs at relatively low temperatures. The particles emit from cyan blue to far-red, and are successfully used in cellular imaging (see figure).

Evidence for an Additional Metastatic Route: In Vivo Imaging of Cancer Cells in the Primo-Vascular System Around Tumors and Organs

PurposeResearchers have been studying the mechanisms by which metastasis can be prevented via blocking the hematogenous and the lymphatic routes for a long time now. However, metastasis is still the single most challenging obstacle for successful cancer management. In a new twist that may require some retooling of this established approach, we investigated the hypothesis that tumor metastases can occur via an independent fluid-conducting system called the primo-vascular system.ProceduresThe dissemination and growth of near-infrared quantum dot (NIR QD)-electroporated cancer cells in metastatic sites were investigated using in vivo multispectral imaging techniques.ResultsOur results show that the NIR QD-labeled cancer cells were able to migrate through not only the blood vascular and lymphatic systems but also the primo-vascular system extending from around the tumor to inside the abdominal cavity. Furthermore, the NIR QD-labeled cancer cells, which had been seeded intraperitoneally, specifically infiltrated the primo-vascular system in the omentum and in the gonadal fat.ConclusionsThese findings strongly suggest that the primo-vascular system may be an additional metastasis route, complementing the lymphatic and hematogenous routes, which facilitate the dissemination and colonization of cancer cells at secondary sites.

Time Consumption Reduction of Ray Tracing for Rcs Prediction using Efficient Grid Division and Space Division Algorithms

This paper introduces a fast and efficient algorithm to calculate the radar cross section of complex targets using shooting and bouncing rays. The method combines a multiresolution grid division algorithm, with an algorithm that divides space using an octree structure. Applying the two division algorithms simultaneously, accelerates computation speed in ray tracing without reducing accuracy. Numerical results show the accuracy and efficiency of the proposed method.

Electrospun polymer/quantum dot composite fibers as down conversion phosphor layers for white light-emitting diodes

Color control without severe photoluminescence (PL) quenching is one of main issues in white light emission technology. White light emission was successfully achieved using phosphor layers made of electrospun quantum dot (QD) embedded polymer fibers as color down-conversion layers of blue light-emitting diodes (LEDs). Down-conversion from blue to longer wavelength was characterized by fluorescence microscopy and photoluminescence (PL) spectroscopy. Using orange QD-embedded fiber-based phosphor layers, a broad spectrum of white-light was demonstrated with the CIE coordination of (0.367, 0.367). The QDs in the polymer fiber matrix did not show the aggregation of QDs unlike the QDs in a thin film matrix. Furthermore, from Time-Correlated Single Photon Counting (TCSPC) analysis, the QDs in fiber mats have longer PL lifetime (∼3.95 ns) than that in a thin film matrix (∼3.20 ns) due to the lower aggregation-induced luminescence concentration quenching. Our results suggest that the simple electrospinning method may be a very good method to obtain uniform and bright QD phosphors for white LEDs which can be used for solid-state illumination sources and lighting devices.

Layer-by-Layer Quantum Dot Assemblies for the Enhanced Energy Transfers and Their Applications toward Efficient Solar Cells

Two different quantum dots (QDs) with an identical optical band gap were prepared: one without the inorganic shell and short surface ligands (BQD) and the other with thick inorganic shells and long surface ligands (OQD). They were surface-derivatized to be positively or negatively charged and were used for layer-by-layer assemblies on TiO2. By sandwiching BQD between OQD and TiO2, OQD photoluminescence showed seven times faster decay, which is attributed to the combined effect of the efficient energy transfer from OQD to BQD with the FRET efficiency of 86% and fast electron transfer from BQD to TiO2 with the rate of 1.2 × 10(9) s(-1). The QD bilayer configuration was further applied to solar cells, and showed 3.6 times larger photocurrent and 3.8 times larger photoconversion efficiency than those of the device with the OQD being sandwiched by BQD and TiO2. This showcases the importance of sophisticated control of QD layer assembly for the design of efficient QD solar cells.

Strategy for synthesizing quantum dot-layered double hydroxide nanocomposites and their enhanced photoluminescence and photostability.

Layered double hydroxide-quantum dot (LDH-QD) composites are synthesized via a room temperature LDH formation reaction in the presence of QDs. InP/ZnS (core/shell) QD, a heavy metal free QD, is used as a model constituent. Interactions between QDs (with negative zeta potentials), decorated with dihydrolipoic acids, and inherently positively charged metal hydroxide layers of LDH during the LDH formations are induced to form the LDH-QD composites. The formation of the LDH-QD composites affords significantly enhanced photoluminescence quantum yields and thermal- and photostabilities compared to their QD counterparts. In addition, the fluorescence from the solid LDH-QD composite preserved the initial optical properties of the QD colloid solution without noticeable deteriorations such as red-shift or deep trap emission. Based on their advantageous optical properties, we also demonstrate the pseudo white light emitting diode, down-converted by the LDH-QD composites.

In vivo imaging of cancer cells with electroporation of quantum dots and multispectral imaging

Our understanding of dissemination and growth of cancercells is limited by our inability for long-term followup of this process in vivo. Fluorescence molecular imaging has the potential to track cancercells with high contrast and sensitivity in living animals. For this purpose, intracellular delivery of near-infraredfluorescencequantum dots(QDs) by electroporation offers considerable advantages over organic fluorophores and other cell tagging methods. In this research we developed a multispectral imaging system that could eliminate two major parameters compromising in vivofluorescenceimaging performance, i.e., variations in the tissue optical properties and tissueautofluorescence. We demonstrated that electroporation of QDs and multispectral imaging allowed in vivo assessment of cancer development and progression in the xenograft mouse tumor model for more than 1 month, providing a powerful means to learn more about the biology of cancer and metastasis.

Optimized Design of Radar Absorbing Materials for Complex Targets

In this paper, we present a hybrid technique for designing RAM optimally to reduce the RCS of complex targets in a wide-band frequency range. The technique combines a high-frequency method and a genetic algorithm (GA) to obtain an optimal RAM in complex targets. By the virtue of the high-frequency method, such as the physical optics (PO) method and the method of equivalent currents (MEC), the proposed technique can be applied to complex targets with relative ease. However, the high-frequency method needs a classification of shadow regions as pre-processing. A Z-buffer algorithm is employed in this process. The procedure results in designing the optimal RAM which significantly reduces the RCS of complex targets.

Novel Synthesis of Porous Silver Nanostructures Using a Starch Template and Their Applications toward Plasmonic Sensors

Novel Synthesis of Porous Silver Nanostructures Using a Starch Template and Their Applications toward Plasmonic Sensors A novel method to prepare nanoporous silver structures (NPSs) is introduced. Soluble starch is used as the in situ template, and an aqueous AgNO3 solution is used as the silver precursor. The porous NPS film is introduced in a plasmonic sensor using the Kretschmann configuration. The obtained device responds well to environmental reflective-index changes.