Kyung Jin Son

Photosensitizing hollow nanocapsules for combination cancer therapy

The social and economic burden of cancer demands a spectrum of therapeutic methodologies. Current options include surgery, chemotherapy, radiotherapy, hyperthermia, and photodynamic therapy (PDT). Only rarely, however, is a single methodology sufficient to overcome cancer. This requirement has inspired combination regimens that overcome the additive, synergistic, and complementary interactions between treatments. An important advance in combination cancer therapy was achieved with the fabrication of multifunctional nanomaterials, including polymeric micelles and nanoparticles (NPs), which may be used to simultaneously perform more than one therapy. Polymeric multilayer capsules present several advantages in combination cancer therapy, including a relatively high capacity for the active substance and versatility in fabrication of the capsule shell. The hollow capsules are assembled in a layer-by-layer (LbL) process onto a sacrificial template followed by dissolution of the template. Hollow polymeric capsules can be fabricated by using templates that vary in size from a few nanometers to hundreds of micrometers, and their chemical and mechanical properties can be precisely tailored by modulating the thickness and composition of the shell. Polymeric multilayer capsules attract interest in various fields of research, and most recently for their high loading capacity as vehicles in drug delivery systems (DDSs). Based on this background, we developed a new type of hollow nanocapsule (NC) for use in combining PDT with chemotherapy. To produce the photosensitizer, we synthesized a negatively charged dendritic porphyrin (DP) that was shown to be effective photosensitizer for PDT, and combined it as a bilayer component with poly(allylamine hydrochloride) (PAH) to fabricate hollow NCs. In general, photosensitizers have large p-conjugation domains for high quantum yields and effective energy absorption. Therefore, many photosensitizers can easily form aggregates in aqueous media because of their abilities to form p–p interactions and their hydrophobic characteristics, which provide a self-quenching effect of the excited state. Unlike conventional photosensitizers, DP has large dendritic wedges that effectively prevent self-quenching phenomena. Moreover, when the DP forms self-assembled nanostructures such as polymeric micelles, large numbers of DPs can effectively generate a high concentration of singlet oxygen at local sites in order to overcome the threshold concentration for oxidative damage. The (PAH/DP)n multilayer nanocapsules were filled with doxorubicin (DOX), a model anticancer drug, in order to implement chemotherapy. While most NC shells used in DDS are prepared from linear polyelectrolytes that lack any function other than drug container, our system employs DP as not only a polyelectrolyte for the formation of NC shells but also as photosensitizing units for photodynamic therapy. Figure 1 shows the preparation of hollow NCs by alternating deposition of PAH and DP onto a negatively charged polystyrene (PS) NP and the subsequent removal of the template PS NP. The average molecular weight of PS was determined to be 70 kDa by GPC analysis. It has been reported that dissolved PS (Mw 10 Da) can diffuse through the multilayer shells when they were extracted with organic solvents such as chloroform or tetrahydrofuran. The DP used in this study bears 32 carboxylate groups on its periphery and a negative zeta potential ( 31.0 mV) at pH 7.4. We expected that multilayer shells would be formed by this LbL deposition technique based on the electrostatic interaction between positively charged PAH and negatively charged DP. The stepwise formation of multilayer shells onto PS NPs was monitored by observing zeta potential changes of particles after each deposition step (Figure 2a). The bare PS NPs have a zeta potential of approximately 55 mV. The PS NPs coated with layers of PAH and DP showed discrete zeta potentials that alternate between positive or negative, depending on the outer layer type. This observation showed that the multilayer surface was charge-overcompensated in each adsorption step, which facilitated adsorption of the next oppositely charged capsule shell layer. Owing to the strong UV/Vis absorbance and fluorescence (FL) emission of DP, multilayer formation could be monitored by changes in UV/Vis absorbance and FL emission from the multilayer-coated PS particles (NCn PS; n = numbers of LbL bilayer, n = 1–3). As shown in Figure 2b, the UV/Vis absorbance and FL emission increased with the number of bilayers. Quantities of DP deposited in NCs were determined to be (106.2 0.4), (212.6 0.4), and (366.1 [*] K. J. Son, Y. Lee, Prof. W.-G. Koh Department of Chemical and Biomolecular Engineering Yonsei University 50 Yonsei-ro, Seodaemoon-Gu, Seoul 120-749 (Korea) E-mail: wongun@yonsei.ac.kr H.-J. Yoon, J.-H. Kim, Prof. W.-D. Jang Department of Chemistry, Yonsei University 50 Yonsei-ro,Seodaemoon-Gu, Seoul 120-749 (Korea) E-mail: wdjang@yonsei.ac.kr [] These authors contributed equally to this work.

Efficiency improvement of dye-sensitized solar cells using graft copolymer-templated mesoporous TiO2 films as an interfacial layer

Organized mesoporous TiO2 films with high porosity and good connectivity were synthesized via sol–gel by templating an amphiphilic graft copolymer consisting of poly(vinyl chloride) backbone and poly(oxyethylene methacrylate) side chains, i.e., PVC-g-POEM. The randomly microphase-separated graft copolymer was self-reorganized to exhibit a well-ordered micellar morphology upon controlling polymer–solvent interactions, as confirmed by atomic force microscope (AFM) and glazing incidence small-angle X-ray scattering (GISAXS). These organized mesoporous TiO2 films, 550 nm in thickness, were used an an interfacial layer between a nanocrystalline TiO2 thick layer and a conducting glass in dye-sensitized solar cells (DSSC). Introduction of the organized mesoporous TiO2 layer resulted in the increased transmittance of visible light, decreased interfacial resistance and enhanced electron lifetime. As a result, an energy conversion efficiency of DSSC employing polymer electrolyte was significantly improved from 3.5% to 5.0% at 100 mW cm−2.

Fabrication of hydrogel-micropatterned nanofibers for highly sensitive microarray-based immunosensors having additional enzyme-based sensing capability

Nanofiber-based protein microarrays were fabricated through a combination of electrospinning and hydrogel lithography. Electrospinning generated polystyrene (PS)/poly(styrene-alt-maleic anhydride) (PSMA) fibers with diameters ranging from 0.5 to 1.0 µm and photopatterning of poly(ethylene glycol) (PEG) hydrogel on the electrospun fibers created clearly defined hydrogel microstructures with incorporated nanofibers. The resultant micropatterned nanofibrous substrates were obtained as freestanding and bidirectionally porous sheets, where most of the nanofibers were inserted through the side walls of the hydrogel microstructures. Because of the protein-repellent nature of PEG hydrogels, IgG was selectively immobilized only within the nanofibrous region, creating an IgG microarray. Due to increased surface area, IgG loading in nanofibrous substrates was about six times greater than on planar substrates, which consequently yielded a higher fluorescence signal and faster reaction rate in immunoassays. The capability of encapsulating enzymes made it possible for PEG hydrogels to be used not only for defining protein micropatterns but also for additional biosensor elements. Based on this result, micropatterned nanofibrous substrates consisting of IgG-immobilized nanofibers and enzyme-entrapping PEG hydrogels were fabricated, and their potential to simultaneously carry out both immunoassays and enzyme-based assays was successfully demonstrated.

Graft Copolymer-Templated Mesoporous TiO2 Films Micropatterned with Poly(ethylene glycol) Hydrogel: Novel Platform for Highly Sensitive Protein Microarrays

In this study, we describe the use of organized mesoporous titanium oxide (TiO(2)) films as three-dimensional templates for protein microarrays with enhanced protein loading capacity and detection sensitivity. Multilayered mesoporous TiO(2) films with high porosity and good connectivity were synthesized using a graft copolymer consisting of a poly(vinyl chloride) (PVC) backbone and poly(oxyethylene methacrylate) (POEM) side chains as a structure-directing template. The average pore size and thickness of the TiO(2) films were 50-70 nm and 1.5 μm, respectively. Proteins were covalently immobilized onto mesoporous TiO(2) film via 3-aminopropyltriethoxysilane (APTES), and protein loading onto TiO(2) films was about four times greater than on planar glass substrates, which consequently improved the protein activity. Micropatterned mesoporous TiO(2) substrates were prepared by fabricating poly(ethylene glycol) (PEG) hydrogel microstructures on TiO(2) films using photolithography. Because of non-adhesiveness of PEG hydrogel towards proteins, proteins were selectively immobilized onto surface-modified mesoporous TiO(2) region, creating protein microarray. Specific binding assay between streptavidin/biotin and between PSA/anti-PSA demonstrated that the mesoporous TiO(2)-based protein microarrays yielded higher fluorescence signals and were more sensitive with lower detection limits than microarrays based on planar glass slides.

Dendrimer porphyrin-terminated polyelectrolyte multilayer micropatterns for a protein microarray with enhanced sensitivity

Through a combination of layer-by-layer (LbL) self-assembly (SA) and lift-off methods, a dendrimer-coated polyelectrolyte multilayer micropattern was prepared for protein microarrays. A silicon substrate was patterned with a photoresist thin film using conventional photolithography, and then poly(ethyleneimine) (PEI) and poly(sodium 4-styrenesulfonate) (PSS) were alternatively deposited onto the substrate surface using spin-assisted self-assembly. A well-defined multilayer microarray was produced by subsequent removal of the photoresist template by a lift-off process. Dendrimer porphyrin (DP) was successively immobilized onto the PEI-terminated micropatterns via electrostatic interactions between the negatively-charged DPs and positively-charged PEI segments. Because of strong fluorescence from focal porphyrins, the homogeneous covering of DPs onto the multilayer micropatterns was easily confirmed using fluorescence microscopy. Atomic force microscopy (AFM) also showed morphological change of micropatterned surfaces by DP immobilization. Based on these results, IgG was immobilized on the DP-coated protein microarrays, and immunoassays were performed to demonstrate that the DP-coated microarrays yielded a higher fluorescence signal and were more sensitive than the control microarrays that were coated with linear PAA polymer instead of DP due to the multiple functional groups present on the DP-coated arrays and their increased surface area relative to control microarrays.

Induced Transition of CdSe Nanoparticle Superstructures by Controlling the Internal Flow of Colloidal Solution

The self-assembly behaviors of flow-enhanced CdSe nanoparticle (NP) colloidal systems were investigated, which were systemically prepared by adding ethylene glycol (EG) or acetic acid (AA) to NP suspensions with deionized water (DI water) base. The additive solvents, which had higher boiling points and lower surface tensions than those of the DI water, modified the internal flow of the NP colloidal system, consequently affecting the morphologies of the generated NP superstructures after the full evaporation of their droplets. In flow-enhanced systems, NPs were formed into highly elongated dendrites that stretched from the center region to the edges along the direction of convective flow inside the droplet, while NPs in random drift system were easily aggregated to form cluster-shaped thick dendritic structures. When the volume fraction of EG was increased, the dominant superstructures were changed from dendrites to clusters, which can be mainly attributed to the changes in the dielectric properties of the NP droplets as evaporation proceeded because of the large discrepancy in the vapor pressures of EG and DI water. The balance between the interparticle potentials of electrostatic repulsion and van der Waals attraction was continuously altered, resulting in the formation of clusters with increasing EG ratio. Contrastively, the transition of superstructures could not be observed in the case of colloidal system prepared by mixing DI water and AA, which can be ascribed to the similar vapor pressures of the two solvents; the dielectric properties of the solution mixture was barely changed throughout the steady evaporation process, which resulted in the formation of uniformly distributed highly elongated dendrites. Polarization-dependent imaging experiments and photoluminescence measurements revealed that the stretched dendrites formed under the flow-enhanced conditions showed higher crystallinity than that of the clusters.