Ting-Yu Liu

Synthesis and characterizations of Ni-NiO nanoparticles on PDDA-modified graphene for oxygen reduction reaction

We are presenting our recent research results about the Ni-NiO nanoparticles on poly-(diallyldimethylammonium chloride)-modified graphene sheet (Ni-NiO/PDDA-G) nanocomposites prepared by the hydrothermal method at 90°C for 24 h. The Ni-NiO nanoparticles on PDDA-modified graphene sheets are measured by transmission electron microscopy (TEM), energy-dispersive X-ray spectroscopy (EDS), and selected area electron diffraction (SAED) pattern for exploring the structural evidence to apply in the electrochemical catalysts. The size of Ni-NiO nanoparticles is around 5 nm based on TEM observations. The X-ray diffraction (XRD) results show the Ni in the (012), (110), (110), (200), and (220) crystalline orientations, respectively. Moreover, the crystalline peaks of NiO are found in (111) and (220). The thermal gravimetric analysis (TGA) result represents the loading content of the Ni metal which is about 34.82 wt%. The electron spectroscopy for chemical analysis/X-ray photoelectron spectroscopy (ESCA/XPS) reveals the Ni0 to NiII ratio in metal phase. The electrochemical studies with Ni-NiO/PDDA-G in 0.5 M aqueous H2SO4 were studied for oxygen reduction reaction (ORR).

Label-free and culture-free microbe detection by three dimensional hot-junctions of flexible Raman-enhancing nanohybrid platelets

Novel nanohybrid arrays of silver (Ag)-on-silicate platelets with flexibility and three-dimensional (3D) hot-junctions (particularly in z-direction) were discovered for improving the stability of free nanoparticles and the mobility of rigid (glass or silicon-based) substrates in surface-enhanced Raman scattering (SERS) detection technology. Since the Ag nanoparticles are adsorbed on both sides of few nanometer-thick silicate platelets (single-layer exfoliated clay), the geometric arrangement of Ag on both sides of the nanoplatelets (Ag/NSP) may induce strong hot-junctions (z-direction) in reference to the pristine montmorillonite clay (multi-layers) at the thickness of ∼20 nm, measured by small molecules (adenine of DNA) and bacteria (S. aureus). Enormous red-shifts (16 nm wavelength difference) were observed between single layer and multi-layer silicate platelets, showing that huge surface plasmon enhancement comes from hot junctions in the z-direction (∼7 times higher than 2D hot-junctions of traditional SERS biochips). Further, the Ag/NSP SERS substrate displays a free floating mobility and optical transparency (less background interference), which inherently increase the contacted surface-area between the substrate and microorganisms, to enhance the SERS sensitivity. The surface modulation with a surfactant could be complimentary towards a variety of microorganisms including hydrophobic microbes, irregular-shaped microorganisms and larger biological cells due to their mutual specific surface interactions. It was anticipated to apply in the rapid detection for varied microbes with label-free and culture-free characterizations.

Novel pH-sensitive drug carriers of carboxymethyl-hexanoyl chitosan (Chitosonic® Acid) modified liposomes

In this study, novel hybrid nanocarriers composed of carboxymethyl-hexanoyl chitosan (Chitosonic® Acid, CA) and 1,2-distearoyl-sn-glycero-3-phosphoethanolamine (DSPE)-liposomes were developed. CA was immobilized onto the DSPE-liposomes by EDC/NHS reaction using the carboxyl group of CA and the amino group of DSPE. The characteristics of the resultant CA-modified liposomes were evaluated by transmission electron microscopy, dynamic light scattering, zeta potential, FTIR spectroscopy, X-ray photoelectron spectroscopy, and contact angle measurement. The results show that the particle size and surface charge of the CA-modified liposomes varied with the concentration of CA, and exhibited pH-sensitive behavior. In vitro drug release studies demonstrated the sustained release behavior of the doxorubicin in the CA-modified liposomes, related to the rapid release in the free doxorubicin. Interestingly, the doxorubicin release rate from CA-modified liposomes was lower at higher pH values (pH 7.4) than at lower pH values (pH 4), indicating that the drug carrier displayed pH-sensitive released behavior. Furthermore, CA-modified liposomes exhibited no cytotoxicity toward the fibroblast cells (L-929 cells), suggesting an excellent biocompatibility. Fluorescence and confocal microscopy images showed good cellular internalization of the CA-modified liposomes into the cellular compartment. These results confirm that the novel CA-modified liposomes could respond to pH environment, which is promising for drug controlled release applications, especially in the field of cancer cell therapy (lower pH environments).

Magnetically triggered nanovehicles for controlled drug release as a colorectal cancer therapy

Magnetic silica core/shell nanovehicles presenting atherosclerotic plaque-specific peptide-1 (AP-1) as a targeting ligand (MPVA-AP1 nanovehicles) have been prepared through a double-emulsion method and surface modification. Amphiphilic poly(vinyl alcohol) was introduced as a polymer binder to encapsulate various drug molecules (hydrophobic, hydrophilic, polymeric) and magnetic iron oxide (Fe3O4) nanoparticles. Under a high-frequency magnetic field, magnetic carriers (diameter: ca. 50 nm) incorporating the anti-cancer drug doxorubicin collapsed, releasing approximately 80% of the drug payload, due to the heat generated by the rapidly rotating Fe3O4 nanoparticles, thereby realizing rapid and accurate controlled drug release. Simultaneously, the magnetic Fe3O4 themselves could also kill the tumor cells through a hyperthermia effect (inductive heating). Unlike their ungrafted congeners (MPVA nanovehicles), the AP1-grafted nanovehicles bound efficiently to colorectal cancer cells (CT26-IL4Rα), thereby displaying tumor-cell selectivity. The combination of remote control, targeted dosing, drug-loading flexibility, and thermotherapy and chemotherapy suggests that magnetic nanovehicles such as MPVA-AP1 have great potential for application in cancer therapy.

Self-assembly behaviors of thermal- and pH- sensitive magnetic nanocarriers for stimuli-triggered release

In the present work, we prepare thermo- and pH-sensitive polymer-based nanoparticles incorporating with magnetic iron oxide as the remote-controlled, stimuli-response nanocarriers. Well-defined, dual functional tri-block copolymer poly[(acrylic acid)-block-(N-isopropylacrylamide)-block-(acrylic acid)], was synthesized via reversible addition-fragmentation chain-transfer (RAFT) polymerization with S,S′-bis(α,α′-dimethyl-α″-acetic acid)trithiocarbonate (CMP) as a chain transfer agent (CTA). With the aid of using 3-aminopropyltriethoxysilane, the surface-modified iron oxides, Fe3O4-NH2, was then attached on the surface of self-assembled tri-block copolymer micelles via 1-[3-(dimethylamino)propyl]-3-ethylcarbodiimide hydrochloride/N-hydroxysuccinamide (EDC/NHS) crosslinking method in order to furnish not only the magnetic resources for remote control but also the structure maintenance for spherical morphology of our nanocarriers. The nanocarrier was characterized by transmission electron microscope (TEM), Fourier transform infrared spectroscopy (FT-IR), and ultraviolet–visible (UV/Vis) spectral analysis. Rhodamine 6G (R6G), as the modeling drugs, was encapsulated into the magnetic nanocarriers by a simple swelling method for fluorescence-labeling and controlled release monitoring. Biocompatibility of the nanocarriers was studied via 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay, which revealed that neither the pristine nanocarrier nor the R6G-loaded nanocarriers were cytotoxic to the normal fibroblast cells (L-929 cells). The in vitro stimuli-triggered release measurement showed that the intelligent nanocarriers were highly sensitive to the change of pH value and temperature rising by the high-frequency magnetic field (HFMF) treatment, which provided the significant potential to apply this technology to biomedical therapy by stimuli-responsive controlled release.

Influence of magnetic nanoparticle arrangement in ferrogels for tunable biomolecule diffusion

Magnetic sensitive hydrogels (ferrogels) with tunable nanochannels were prepared with poly (vinyl alcohol) (PVA) and iron oxide magnetic nanoparticles under a uniform magnetic field in a freezing–thawing process, evaluated by differential scanning calorimetry (DSC), and the influence of magnetic nanoparticle arrangement on the diffusion behavior of biomolecules was investigated. Nanochannels self-assembled by the arranged magnetic nanoparticles could be tuned by manipulating the direction of the magnetic field, which results in the formation of “needle-like” structures from the magnetic nanoparticles aligned parallel or perpendicular to the permeation direction (anisotropic ferrogels). The effect of biomolecule diffusion between the anisotropic and isotropic ferrogels was observed in a diffusion diaphragm cell (using random nanoparticle dispersions without a magnetic field, as a control). It was established that the parallel-aligned ferrogels exhibit a higher drug diffusion rate compared to the isotropic ferrogels, whereas the perpendicular-aligned ferrogels display the lowest biomolecule diffusion rate. The novel ferrogels were expected to be suitable for application in bio-membranes, and the nanochannels for biomolecule (MW: ca. 0.1–10 kDa) diffusion could be constructed precisely by the magnetic nanoparticle arrangement.

Thermo-responsive nanoarrays of silver nanoparticle, silicate nanoplatelet and PNiPAAm for the antimicrobial applications

The ternary nanohybrids of silver nanoparticles (AgNPs) in combination with silicate nanoplatelets (NSP) and thermally sensitive poly(N-isopropylacrylamide) (PNiPAAm) were fabricated for antibacterial applications. PNiPAAm were chemically grafted on the NSP by atom-transfer radical polymerization (ATRP) via polymerizing N-isopropylacrylamide monomers with sol-gel linkers (BBTES). The nanoparticles of AgNPs then were adsorbed on NSP-PNiPAAm nanosheets through in situ reduction reaction of AgNO3 in aqueous dispersion. The particle sizes of AgNPs were estimated to be 7-12nm in diameter with different composition ratios of AgNPs to NSP-PNiPAAm, evaluated by transmission electron microscope (TEM). The nanohybrids of AgNP/NSP-PNiPAAm exhibited the unique property of lowest critical solution temperature (LCST) at 32°C. The thermo-responsive antibacterial efficacy of the ternary nanohybrids was demonstrated by Bacillus subtilis (B. subtilis) and Escherichia coli (E. coli) at lower than the LCST (28°C) and higher than the LCST (37°C). The result show that the great antibacterial ability was observed in the hydrophilic bacteria (B. subtilis) at 28°C. In contrast, the excellent antibacterial ability was found in the hydrophobic bacteria (E. coli) at 37°C, due to the surface energy modulation of AgNP/NSP-PNiPAAm. The tailoring of silver-containing ternary nanohybrids allow the new antibacterial nanomaterials to selectively affect the surface of bacteria by varying temperature.

Enhancing the photovoltaic performance of dye-sensitized solar cells by modifying TiO2 photoanodes with exfoliated graphene sheets

Exfoliated graphene sheets (EGS) are obtained using simple liquid phase sonication and then mixed with TiO2 nanoparticles in a dye sensitized solar cell photoanode to achieve higher electrical conductivity and faster electron transfer due to much fewer defects as compared to conventional reduced graphene oxide (RGO): ID/IG of 0.256 in EGS as compared with that of 1.128 in RGO. The EGS–TiO2 photoanode yields a conversion efficiency of 8.24%, over a 19% increase compared with that of the RGO–TiO2 photoanode, and a 43% increase over that of TiO2 alone under the same conditions.

Nanohybrid structure analysis and biomolecule release behavior of polysaccharide-CDHA drug carriers

Nanoscaled polymer composites were prepared from polysaccharide chitosan (CS) and Ca-deficient hydroxyapatite (CDHA). CS-CDHA nanocomposites were synthesized by in situ precipitation at pH 9, and the CS-CDHA carriers were then fabricated by ionic cross-linking methods using tripolyphosphate and chemical cross-linking methods by glutaraldehyde and genipin. Certain biomolecules such as vitamin B12, cytochrome c, and bovine serum albumin were loaded into the CS-CDHA carriers, and their release behaviors were investigated. Furthermore, these CS-CDHA carriers were examined by transmission electron microscopy, electron spectroscopy for chemical analysis, and X-ray diffraction. The release behavior of the biomolecules was controlled by the CS/CDHA ratios and cross-linked agents. By increasing the concentration of CS and the concentration of the cross-linking agents, cross-linking within carriers increases, and the release rate of the biomolecules is decreased. Moreover, the release rate of the biomolecules from the CS-CDHA carriers at pH 4 was higher than that at pH 10, displaying a pH-sensitive behavior. Therefore, these CS-CDHA hydrogel beads may be useful for intelligent drug release and accelerate bone reconstruction.

Au Nanoparticles Immobilized on Honeycomb-Like Polymeric Films for Surface-Enhanced Raman Scattering (SERS) Detection

We have successfully developed novel surface-enhanced Raman scattering (SERS) substrates with three-dimensional (3D) porous structures for effectively improving the sensitivity and reproducibility of SERS, which can rapidly detect small molecules (rhodamine 6G as an example). Periodical arrays of the honeycomb-like substrates were fabricated by self-assembling polyurethane-co-azetidine-2,4-dione (PU-PAZ) polymers. PU-PAZ comprising amphiphilic dendrons could stabilize the phase separation between the water droplets and polymer solution, and then organize into regular porous structures during the breath figure method. Subsequently, SERS substrates were fabricated by immobilizing gold nanoparticles (AuNPs) onto the honeycomb-like films with various 3D porous structures, controlled by the different PU-PAZ concentrations and relative humidities. Results show that surface enhancement factors of honeycomb-like substrates were 20 times higher than that of flat-film substrates (control group) due to enormous hot-spots resonance effects by the 3D porous structure, verified through Raman mapping at various positions of the z-axis. Furthermore, the particle size effects were evaluated by immobilized 12 and 67 nm of AuNPs on the honeycomb-like substrates, indicating larger AuNPs could induce more pronounced hot-spots effects. The generation of hot-spots resonance to enhance Raman intensity is strongly dependent on the diameter of AuNPs and the pore size of the honeycomb-like and 3D porous substrates for label-free and rapid SERS detection.