Kang Taek Lee

Theranostic Probe Based on Lanthanide-Doped Nanoparticles for Simultaneous In Vivo Dual-Modal Imaging and Photodynamic Therapy

Dual-modal in vivo tumor imaging and photodynamic therapy using hexagonal NaYF(4):Yb,Er/NaGdF(4) core-shell upconverting nanoparticles combined with a photosensitizer, chlorin e6, is reported. Tumors can be clearly observed not only in the upconversion luminescence image but also in the magnetic resonance image. In vivo photodynamic therapy by systemic administration is demonstrated under 980 nm irradiation.

Long-Term Real-Time Tracking of Lanthanide Ion Doped Upconverting Nanoparticles in Living Cells†

Recently, there has been great interest in employing nanoparticles for various biological applications. Nanoparticles can be synthesized in a controlled manner such that they have desirable sizes, shapes, and optical or magnetic properties. In addition, one may provide nanoparticles with biological functions through chemical surface modifications and conjugation of ligands. Such intrinsic and extrinsic properties of nanoparticles enable them to be used as excellent biological imaging probes and diagnostic/therapeutic agents at the cellular level. Among the various nanoparticle systems developed thus far, semiconductor nanocrystals or quantum dots (QDs) are most widely used. QDs are extremely bright and photostable, and exhibit excellent spectral properties (i.e., broad absorption and narrow emission bands) suited for multicolor detection. However, the drawbacks such as photoblinking, the presence of nonradiant dark particles, and potential cytotoxicity limit their applicability. In recent years, several alternative types of luminescent nanoparticles have been introduced for biological applications. For example, nanodiamonds (NDs) with nitrogen vacancy centers were found to be highly photoluminescent while exhibiting no photoblinking and photobleaching, 11] and even useful as the imaging probe for super-resolution optical microscopy. However, applying NDs for biological imaging has limitations, especially in the case of long-term tracking studies, since the excitation in the blue or green region (typically 488 or 532 nm) might result in fatal photodamage to cells or low penetration depth into tissues. In contrast, single-walled carbon nanotubes (SWNTs) were shown to be appropriate for biological imaging in that the excitation and emission lie in the near-infrared (NIR) spectral range. However, being longer than 100 nm typically, SWNTs are considered to be too large to be used as biolabels. Meanwhile, lanthanide ion doped upconverting nanoparticles (UCNPs), which emit in the visible range upon absorption of NIR photons, have attracted great attention owing to their unique optical properties. First, two-photon upconversion of NIR excitation to the emission of a visible photon is so efficient that a tiny continuous-wave (CW) diode laser (980 nm) with the output of tens of milliwatts is sufficient as the excitation source. Second, by employing NIR excitation, one can suppress cellular autofluorescence, induce little photodamage to living cells, and achieve relatively deep penetration into tissues. Finally, UCNPs exhibit neither photoblinking on the millisecond and second time scales nor photobleaching even with hours of continuous excitation, 21] their cytotoxicity is very low, 22] and the inclusion or doping of Gd ions in the host materials endows UCNPs with an additional modality for magnetic resonance imaging (MRI). 23] As a result, UCNPs became one of the most promising nanoparticle systems for biological imaging and there are continuing efforts to improve their properties (e.g., increasing luminescence intensity and reducing the particle size) by designing new synthetic strategies. Herein, we report the first real-time tracking study with UCNPs at the single vesicle level in living cells. Thanks to the remarkable photostability of UCNPs and the noninvasiveness of NIR excitation, we were able to visualize the intracellular movements of UCNPs for as long as 6 h without interruption. We first assessed the benefits of using NIR radiation as the excitation source to demonstrate the feasibility of long-term live-cell imaging with UCNPs. The UCNPs (hexagonal-phase NaYF4 co-doped with Yb 3+ and Er, ca. 30 nm in diameter) coated by amphiphilic PEG–phospholipids (PEG = poly(ethylene glycol)) were internalized into HeLa cells and imaged on a home-made epi-fluorescence microscope setup (Methods section and Figures S1 and S2 in the Supporting [*] Dr. S. H. Nam, Y. M. Bae, Dr. H. M. Kim, Dr. K. T. Lee, Dr. Y. D. Suh Laboratory for Advanced Molecular Probing (LAMP) NanoBio Fusion Research Center, Korea Research Institute of Chemical Technology, Daejeon 305-600 (Korea) Fax: (+ 82)42-860-7164 E-mail: ktlee@krict.re.kr ydsuh@krict.re.kr Y. I. Park, Dr. J. H. Kim, Prof. Dr. T. Hyeon National Creative Research Initiative Center for Oxide Nanocrystalline Materials, World Class University (WCU) Program of Chemical Convergence for Energy & Environment (C2E2) School of Chemical and Biological Engineering, Seoul National University, Seoul 151-744 (Korea) Y. M. Bae, Prof. Dr. J. S. Choi Department of Biochemistry, Chungnam National University Daejeon 305-764 (Korea) [] These authors contributed equally to this work.

Even-odd alternation in mass spectrum of thymine and uracil clusters: Evidence of intracluster photodimerization

Multiphoton ionization of thymine and uracil clusters generated by a supersonic molecular beam gave rise to a remarkable alternation of mass spectral intensities between even- and odd-numbered clusters. Such alternation was observed in clusters of up to 30 molecules. Excitation to the two lowest electronically excited states seemed to be a strong prerequisite. In view of the well known photodimerization reaction of thymine and uracil in the bulk phase, it is proposed that such alternation in the mass spectral intensity resulted from formation of photodimer units within the cluster on intense UV irradiation. Several analogues of thymine with no known propensity for photodimerization in the bulk phase did not exhibit any sign of such alternation in the cluster mass spectrum. The intrinsic UV window for photodimerization, and hence photoinduced mammalian mutagenesis, was estimated to be approximately 210–280 nm, significantly narrower than the previously reported bulk values of 150–300 nm.

Ever-fluctuating single enzyme molecules

Nat. Chem. Biol. 2, 87–94 (2006) In the print version of this article and the version initially published online, the subsection “Estimation of tetramer dissociation” of the Methods contained an error. The second sentence should read: “To determine the timescale of tetramer dissociation, we recordedthe enzymatic activity, as a function of time, of 20 pM of biotin-linked β-galactosidase immobilized on 1-μm-diameter streptavidin-coated beads present in excess”. The error has been corrected in the HTML and PDF versions of the article. This correction has been appended to the PDF version.

Synthesis of upconversion nanoparticles conjugated with graphene oxide quantum dots and their use against cancer cell imaging and photodynamic therapy

Multifunctional nanocomposite has a huge potential for cell imaging, drug delivery, and improving therapeutic effect with less side effects. To date, diverse approaches have been demonstrated to endow a single nanostructure with multifunctionality. Herein, we report the synthesis and application of core-shell nanoparticles composed with upconversion nanoparticle (UCNP) as a core and a graphene oxide quantum dot (GOQD) as a shell. The UCNP was prepared and applied for imaging-guided analyses of upconversion luminescence. GOQD was prepared and employed as promising drug delivery vehicles to improve anti-tumor therapy effect in this study. Unique properties of UCNPs and GOQDs were incorporated into a single nanostructure to provide desirable functions for cell imaging and drug delivery. In addition, hypocrellin A (HA) was loaded on GOQDs for photo-dynamic therapy (PDT). HA, a commonly used chemotherapy drug and a photo-sensitizer, was conjugated with GOQD by π-π interaction and loaded on PEGylated UCNP without complicated synthetic process, which can break structure of HA. Applying these core-shell nanoparticles to MTT assay, we demonstrated that the UCNPs with GOQD shell loaded with HA could be excellent candidates as multifunctional agents for cell imaging, drug delivery and cell therapy.

Enhanced splicing correction effect by an oligo-aspartic acid–PNA conjugate and cationic carrier complexes

Peptide nucleic acids (PNAs) are synthetic structural analogues of DNA and RNA. They recognize specific cellular nucleic acid sequences and form stable complexes with complementary DNA or RNA. Here, we designed an oligo-aspartic acid-PNA conjugate and showed its enhanced delivery into cells with high gene correction efficiency using conventional cationic carriers, such as polyethylenimine (PEI) and Lipofectamine 2000. The negatively charged oligo-aspartic acid-PNA (Asp(n)-PNA) formed complexes with PEI and Lipofectamine, and the resulting Asp(n)-PNA/PEI and Asp(n)-PNA/Lipofectamine complexes were introduced into cells. We observed significantly enhanced cellular uptake of Asp(n)-PNA by cationic carriers and detected an active splicing correction effect even at nanomolar concentrations. We found that the splicing correction efficiency of the complex depended on the kind of the cationic carriers and on the number of repeating aspartic acid units. By enhancing the cellular uptake efficiency of PNAs, these results may provide a novel platform technology of PNAs as bioactive substances for their biological and therapeutic applications.