Joonhyuck Park

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.

Hyaluronic Acid−Quantum Dot Conjugates for In Vivo Lymphatic Vessel Imaging

A simple and novel electrostatic coupling method is reported, which provides a hyaluronic acid-quantum dot conjugate (HA-QD) that is colloidally stable and size-tunable from 50 to 120 nm. The HA-QDs show cancer targeting efficiency, which suggests diagnostic and imaging applications. The conjugates are also demonstrated for the fluorescence staining capability for lymphatic vessels in vitro and in vivo. Using the HA-QDs in a small animal model, lymphatic vessels are visualized real-time in vivo for days. Comprehensive cytotoxicity evaluations are made for the conjugates and the unconjugated counterpart. The HA-QDs showcase the potentials toward cancer imaging and real-time visualization of changes in lymphatic vessels such as lymphangiogenesis.

Imaging Depths of Near-Infrared Quantum Dots in First and Second Optical Windows

Potential advantages of quantum dot (QD) imaging in the second optical window (SOW) at 1,000 to 1,400 nm over the first optical window (FOW) at 700 to 900 nm have attracted much interest. QDs that emit at 800 nm (800QDs) and QDs that emit at 1,300 nm (1,300QDs) are used to investigate the imaging depths at the FOW and SOW. QD images in biologic tissues are processed binarized via global thresholding method, and the imaging depths are determined using the criteria of contrast to noise ratio and relative apparent size. Owing to the reduced scattering in the SOW, imaging depth in skin can be extended by approximately three times for 1,300QD/SOW over 800QD/FOW. In liver, excitation of 1,300QD/SOW can be shifted to longer wavelengths; thus, the imaging depth can be extended by 1.4 times. Effects of quantum yield (QY), concentration, incidence angle, polarization, and fluence rate F on imaging depth are comprehensively studied. Under F approved by the Food and Drug Administration, 1,300QDs with 50% QY can reach imaging depths of 29.7 mm in liver and 17.5 mm in skin. A time-gated excitation using 1,000 times higher F pulses can obtain the imaging depth of ≈ 5 cm. To validate our estimates, in vivo whole-body imaging experiments are performed using small-animal models.

Quantum Dots in an Amphiphilic Polyethyleneimine Derivative Platform for Cellular Labeling, Targeting, Gene Delivery, and Ratiometric Oxygen Sensing.

Amphiphilic polyethyleneimine derivatives (amPEIs) were synthesized and used to encapsulate dozens of quantum dots (QDs). The QD-amPEI composite was ∼100 nm in hydrodynamic diameter and had the slightly positive outer surface that suited well for cellular internalization. The QD-amPEI showed very efficient QD cellular labeling with the labeled cell fluorescence intensity more than 10 times higher than conventional techniques such as Lipofectamine-assisted QD delivery. QD-amPEI was optimal for maximal intracellular QD delivery by the large QD payload and the rapid endocytosis kinetics. QD-amPEI platform technology was demonstrated for gene delivery, cell-specific labeling, and ratiometric oxygen sensing. Our QD-amPEI platform has two partitions: positive outer surface and hydrophobic inside pocket. The outer positive surface was further exploited for gene delivery and targeting. Co-delivery of QDs and GFP silencing RNAs was successfully demonstrated by assembling siRNAs to the outer surfaces, which showed the transfection efficiency an order of magnitude higher than conventional gene transfections. Hyaluronic acids were tethered onto the QD-amPEI for cell-specific targeted labeling which showed the specific-to-nonspecific signal ratio over 100. The inside hydrophobic compartment was further applied for cohosting oxygen sensing phosphorescence Ru dyes along with QDs. The QD-Ru-amPEI oxygen probe showed accurate and reversible oxygen sensing capability by the ratiometric photoluminescence signals, which was successfully applied to cellular and spheroid models.

Spraying Quantum Dot Conjugates in the Colon of Live Animals Enabled Rapid and Multiplex Cancer Diagnosis Using Endoscopy

The detection of colon cancer using endoscopy is widely used, but the interpretation of the diagnosis is based on the clinicians naked eye. This is subjective and can lead to false detection. Here we developed a rapid and accurate molecular fluorescence imaging technique using antibody-coated quantum dots (Ab-QDs) sprayed and washed simultaneously on colon tumor tissues inside live animals, subsequently excited and imaged by endoscopy. QDs were conjugated to matrix metalloproteinases (MMP) 9, MMP 14, or carcinoembryonic antigen (CEA) Abs with zwitterionic surface coating to reduce nonspecific bindings. The Ab-QD probes can diagnose tumors on sectioned mouse tissues, fresh mouse colons stained ex vivo and also in vivo as well as fresh human colon adenoma tissues in 30 min and can be imaged with a depth of 100 μm. The probes successfully detected not only cancers that are readily discernible by bare eyes but also hyperplasia and adenoma regions. Sum and cross signal operations provided postprocessed images that can show complementary information or regions of high priority. This multiplexed quantum dot, spray-and-wash, and endoscopy approach provides a significant advantage for detecting small or flat tumors that may be missed by conventional endoscopic examinations and bestows a strategy for the improvement of cancer diagnosis.

Simultaneous phase and size control in the synthesis of Cu2SnS3 and Cu2ZnSnS4 nanocrystals

Facile and rapid one-pot synthesis of nearly monodisperse Cu2SnS3 and Cu2ZnSnS4 nanocrystals was developed using a heating up method. Their crystalline phase and size were simultaneously controlled by judiciously choosing the sulfur precursor reactivity and the oleic acid content.

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.

Zwitterionic surface coating of quantum dots reduces protein adsorption and cellular uptake.

We have studied the effect of the zwitterionic surface coating of quantum dots (QDs) on their interaction with a serum supplemented cell medium and their internalization by human cervical carcinoma (HeLa) cells. Zwitterionic QDs showed negligible adsorption of human serum albumin (HSA) selected as a model serum protein, in contrast to similar but negatively charged QDs. The incorporation of zwitterionic QDs by HeLa cells was found to be lower than for negatively charged QDs and for positively charged QDs, for which the uptake yield was largest. Our results suggest that the suppression of protein adsorption, here accomplished by zwitterionic QD surfaces, offers a strategy that allows for reducing the cellular uptake of nanoparticles.

Dynamics of nitric oxide rebinding to ferric myoglobin in D 2 O probed by femtosecond mid-IR spectroscopy

The dynamics of diatomic ligands such as O2, CO, and NO binding to ferrous(Fe2+) heme iron of myoglobin have been studied widely due to the physiological importance of reversible binding [1–4]. However, the dynamics of NO with ferric(Fe3+) heme iron of myoglobin is not much studied due to the high reactivity of the heme iron toward NO. The appearance of the multiple bands at 1914, 1927, and 1942 cm−1 in the FT-IR spectrum of wild-type ferric myoglobin(MbIIINO) reveals the conformational heterogeneity, most probably arising from different electrostatic interactions between bound NO and His-64. Since IR spectrum is very sensitive to the protein structure and its environment, IR spectroscopy of the ligand bound myoglobin is an excellent method for probing the ligand binding kinetics of heme proteins, in particular, conformer-dependent rebinding rates.