Chang-Keun Lim

Conjugated Polymer/Photochromophore Binary Nanococktails: Bistable Photoswitching of Near-Infrared Fluorescence for In Vivo Imaging

Nanoscopic dense integration between solid-state emission and photochromism provides nanoprobes capable of photoswitching of bright NIR fluorescence with high on/off contrast, bistability and improved signal identification, being suitable for imaging applications in autofluorescence-rich in vivo environments.

Phthalocyanine-Aggregated Polymeric Nanoparticles as Tumor-Homing Near-Infrared Absorbers for Photothermal Therapy of Cancer

Phthalocyanine-aggregated Pluronic nanoparticles were constructed as a novel type of near-infrared (NIR) absorber for photothermal therapy. Tiny nanoparticles (~ 60 nm, FPc NPs) were prepared by aqueous dispersion of phthalocyanine-aggregated self-assembled nanodomains that were phase-separated from the melt mixture with Pluronic. Under NIR laser irradiation, FPc NPs manifested robust heat generation capability, superior to an individual cyanine dye and cyanine-aggregated nanoparticles. Micro- and macroscopic imaging experiments showed that FPc NPs are capable of internalization into live cancer cells as well as tumor accumulation when intravenously administered into living mice. It is shown here that continuous NIR irradiation of the tumor-targeted FPc NPs can cause phototherapeutic effects in vitro and in vivo through excessive local heating, demonstrating potential of phthalocyanine-aggregated nanoparticles as an all-organic NIR nanoabsorber for hyperthermia.

Gadolinium-coordinated elastic nanogels for in vivo tumor targeting and imaging.

Coordination polymer gels have been recognized as promising hybrid nanoplatforms for imaging and therapeutic applications. Here we report functional metal-organic coordinated nanogels (GdNGs) for in vivo tumor imaging, whose non-crystalline and elastic nature allows for long blood circulation, as opposed to the rapid systemic clearance of common nanohybrids with rigid/crystalline frameworks. The deformable structure of GdNGs was constructed by random crosslinking of highly flexible polyethyleneimines (PEI) with gadolinium (Gd(3+)) coordination. The in vitro characterization revealed that GdNGs have elasticity with an apparent Youngs modulus of 3.0 MPa as well as minimal cytotoxicity owing to the tight chelation of Gd(3+) ions. In contrast to common T1-enhancing gadolinium complexes, GdNGs showed the capability of enhancing negative T2 contrast (r2 = 82.6 mm(-1)s(-1)) due to the Gd(3+)-concentrated nanostructure. Systemic administration of fluorescently labeled GdNGs with core and overall hydrodynamic sizes of ~65 and ~160 nm manifested efficient targeting and dual-modality (magnetic resonance/fluorescence) imaging of tumor in a mouse model. The minimal filtration by the reticuloendothelial system (RES) suggests that the structural deformability helps the large colloids circulate in the blood stream for tumor accumulation. The unusual performance of a large Gd(3+)-complexed colloid (minimal RES sequestration and high T2 contrast enhancement) represents the versatile nature of nanoscopic organic-inorganic hybridization for biomedical applications.

Tuning Solid-State Fluorescence to the Near-Infrared: A Combinatorial Approach to Discovering Molecular Nanoprobes for Biomedical Imaging

Dyes showing solid-state fluorescence (SSF) are intriguing molecules that can emit bright fluorescence in the condensed phase. Because they do not suffer from self-quenching of fluorescence, nanoscopic dense integration of those molecules produces particulate nanoprobes whose emission intensity can be boosted by raising the intraparticle dye density. In spite of the potential promise for imaging applications demanding intense emission signals, their excitation and emission spectra are generally limited to the visible region where biological tissues have less transparency. Therefore, the SSF-based nanoprobes have rarely been applied to noninvasive in vivo imaging. Here we report a combinatorial chemistry approach to attain a high level of tissue transparency of SSF by tuning its excitation and emission wavelengths to the truly near-infrared (NIR) region. We built a dipolar arylvinyl (ArV) scaffold-based chemical library where the optical bandgap could be narrowed to the NIR above 700 nm by combinatorial modulation of the π-electron push-pull strengths. The ArV-aggregated nanoparticles (FArV NPs) with a colloidal size less than 20 nm were formulated using a polymeric surfactant (Pluronic F-127) and applied to bioimaging in cells and in vivo. We demonstrate that some of FArV NPs have truly NIR excitation and emission of SSF, capable of noninvasive in vivo imaging (efficient lymph node mapping and early diagnosis of tumor) in mouse models by virtue of bright solid-state NIR fluorescence and high signal-to-background contrast (S/B ≈ 8) as well as facile circulation in the living body.

Heavy‐Atomic Construction of Photosensitizer Nanoparticles for Enhanced Photodynamic Therapy of Cancer

A new type of heavy-atom-affected Pluronic (F-127) nanoparticle (FIC NP) for photodynamic therapy (PDT) is reported. FIC NPs are formulated with biocompatible constituents, and contain densely integrated iodinated aromatic molecules that form a structurally rigid core matrix and stably encapsulate photosensitizers in a monomeric form. Tiny nanoparticles (≈10 nm) are prepared by aqueous dispersion of photosensitizer-embedded aromatic nanodomains, which self-assemble by phase separation from the Pluronic melt mixture. By using spectroscopic studies and cellular experiments, the following is demonstrated: 1) enhanced singlet-oxygen generation by means of the intraparticle heavy-atom effect on the embedded photosensitizer, 2) facilitated cell uptake due to the small nanoscopic size as well as the Pluronic surface characteristics, and thereby 3) actual enhancement of PDT efficacy for a human breast-cancer cell line (MDA-MB-231), which validates a photophysically motivated nanoformulation approach toward an advanced photosensitizing nanomedicine.

Organelle specific imaging in live cells and immuno-labeling using resonance Raman probe

Raman microspectroscopy is one of the most powerful tools in molecular sensing, offering a non-invasive and comprehensive characterization of the intracellular environment. To analyze and monitor molecular content in specific cellular compartments, different parts of cellular architecture must be unambiguously identified to guide Raman image/spectra acquisition. In this regards, the development of Raman molecular probes, producing spectrally distinct and intense signal is of outmost practical importance. Here we report on a new generation of Raman molecular probes, designed for application in live cells and immuno-labeling, capable of providing unprecedentedly high detection sensitivity through Resonance Raman (RR) enhancement. In contrast to existing Raman markers, the proposed RR reporter is designed to produce RR enhancement under excitation in the visible spectral range, far away from absorption of cellular biomolecules. We show that this concept allows for facile identification of labeled cellular domains, simultaneously with mapping of the macromolecules using spontaneous Raman technique. We demonstrate the breakthrough potential of these RR probes for selective labeling and rapid Raman imaging of membranes as well as mitochondria in live cells. We also show that these resonant Raman probes open the way for Raman-based intracellular immuno-labeling.

Resonance Raman Probes for Organelle-Specific Labeling in Live Cells

Raman microspectroscopy provides for high-resolution non-invasive molecular analysis of biological samples and has a breakthrough potential for dissection of cellular molecular composition at a single organelle level. However, the potential of Raman microspectroscopy can be fully realized only when novel types of molecular probes distinguishable in the Raman spectroscopy modality are developed for labeling of specific cellular domains to guide spectrochemical spatial imaging. Here we report on the design of a next generation Raman probe, based on BlackBerry Quencher 650 compound, which provides unprecedentedly high signal intensity through the Resonance Raman (RR) enhancement mechanism. Remarkably, RR enhancement occurs with low-toxic red light, which is close to maximum transparency in the biological optical window. The utility of proposed RR probes was validated for targeting lysosomes in live cultured cells, which enabled identification and subsequent monitoring of dynamic changes in this organelle by Raman imaging.

Dramatic Enhancement of Quantum Cutting in Lanthanide-Doped Nanocrystals Photosensitized with an Aggregation-Induced Enhanced Emission Dye

Applications of multiphoton processes in lanthanide-doped nanophosphors (NPs) are often limited by relatively weak and narrow absorbance. Here, the concept of an ultimate photosensitization by aggregation-induced enhanced emission (AIEE) dyes to overcome this limitation is introduced. Because AIEE dyes do not suffer from concentration quenching, they can fully cover the NP surface at high density to maximize absorbance while passivating the surface. This concept is applied to multiphoton down-conversion by quantum cutting. Specifically, coating Yb3+/Tb3+-doped NPs with an AIEE dye designed for efficient energy transfer and attachment to the NPs produces a 2260-fold enhancement of multiphoton down-conversion by quantum cutting with remarkable photostability. In a prototypical application, the quantum cutting of UV photons to near-infrared photons that are matched to the band gap of a silicon solar cell produces an average 4% increase in efficiency under concentrated solar illumination. This provides a general strategy for NP photosensitization that can be applied to both multiphoton up- and down-conversion.

Optical Control of Nanoparticle Catalysis Influenced by Photoswitch Positioning in Hybrid Peptide Capping Ligands

Here, we present an in-depth analysis of structural factors that modulate peptide-capped nanoparticle catalytic activity via optically driven structural reconfiguration of the biointerface present at the particle surface. Six different sets of peptide-capped Au nanoparticles were prepared, in which an azobenzene photoswitch was incorporated into one of two well-studied peptide sequences with known affinity for Au, each at one of three different positions: the N- or C-terminus or mid-sequence. Changes in the photoswitch isomerization state induce a reversible structural change in the surface-bound peptide, which modulates the catalytic activity of the material. This control of reactivity is attributed to changes in the amount of accessible metallic surface area available to drive the reaction. This research specifically focuses on the effect of the peptide sequence and photoswitch position in the biomolecule, from which potential target systems for on/off reactivity have been identified. Additionally, trends associated with photoswitch position for a peptide sequence (Pd4) have been identified. Integrating the azobenzene at the N-terminus or central region results in nanocatalysts with greater reactivity in the trans and cis conformations, respectively, however, positioning the photoswitch at the C-terminus gives rise to a unique system that is reactive in the trans conformation and partially deactivated in the cis conformation. These results provide a fundamental basis for new directions in nanoparticle catalyst development to control activity in real time, which could have significant implications in the design of catalysts for multistep reactions using a single catalyst. Additionally, such a fine level of interfacial structural control could prove to be important for applications beyond catalysis, including biosensing, photonics, and energy technologies that are highly dependent on particle surface structures.