Enhancing catalytic activity of TiO2 nanoparticles through acid treatment in Eosin-Y sensitized photohydrogen evolution reaction system.

Light-driven water splitting has gained increasing attention as an eco-friendly method for hydrogen production. There is a pressing need to enhance the performance of catalysts for the commercial viability of this reaction. Many methods have been proposed to improve catalyst performance; however, an economical and straightforward approach remains a priority. This paper presents an uncomplicated technique called acid treatment, which augments the catalytic performance of nanoparticles. The method promotes a change in the catalytic reactivity by causing a deficit in electron density of Ti and O on the surface of TiO2 nanoparticles without altering their size, morphology, or crystal structure. In the Eosin Y sensitized photocatalytic hydrogen production system, nitric acid treated TiO2 (16.95 µmol/g) exhibited 1.5 times the hydrogen production compared to bare TiO2 (11.15 µmol/g).

Multimodal interactions drive chromatin phase separation and compaction.

Gene silencing is intimately connected to DNA condensation and the formation of transcriptionally inactive heterochromatin by Heterochromatin Protein 1α (HP1α). Because heterochromatin foci are dynamic and HP1α can promote liquid-liquid phase separation, HP1α-mediated phase separation has been proposed as a mechanism of chromatin compaction. The molecular basis of HP1α-driven phase separation and chromatin compaction and the associated regulation by trimethylation of lysine 9 in histone 3 (H3K9me3), which is the hallmark of constitutive heterochromatin, is however largely unknown. Using a combination of chromatin compaction and phase separation assays, site-directed mutagenesis, and NMR-based interaction analysis, we show that human HP1α can compact chromatin in the absence of liquid-liquid phase separation. We further demonstrate that H3K9-trimethylation promotes compaction of chromatin arrays through multimodal interactions. The results provide molecular insights into HP1α-mediated chromatin compaction and thus into the role of human HP1α in the regulation of gene silencing.

Phosphatidylserine-dependent structure of synaptogyrin remodels the synaptic vesicle membrane.

Synaptic vesicles are small membrane-enclosed organelles that store neurotransmitters at presynaptic terminals. The uniform morphology of synaptic vesicles is important for brain function, because it enables the storage of well-defined amounts of neurotransmitters and thus reliable synaptic transmission. Here, we show that the synaptic vesicle membrane protein synaptogyrin cooperates with the lipid phosphatidylserine to remodel the synaptic vesicle membrane. Using NMR spectroscopy, we determine the high-resolution structure of synaptogyrin and identify specific binding sites for phosphatidylserine. We further show that phosphatidylserine binding changes the transmembrane structure of synaptogyrin and is critical for membrane bending and the formation of small vesicles. Cooperative binding of phosphatidylserine to both a cytoplasmic and intravesicular lysine-arginine cluster in synaptogyrin is required for the formation of small vesicles. Together with other synaptic vesicle proteins, synaptogyrin thus can sculpt the membrane of synaptic vesicles.

Rapid one-pot synthesis of magnetically separable Fe3O4-Pd nanocatalysts: a highly reusable catalyst for the Suzuki-Miyaura coupling reaction.

Heterogeneous catalysts comprising noble metals and magnetic materials allow a straightforward separation from a reaction using an external magnet and are recovered easily. In this study, we synthesized magnetic Fe3O4-Pdn hybrid heterogeneous catalysts via a rapid one-pot aqueous-phase method. The synthesized Fe3O4-Pd NPs dispersed well with small size (∼50 nm), maintaining high magnetic responsiveness, and showed high reactivity and reusability for the Suzuki-Miyaura coupling reaction between aryl halides and phenylboronic acid. The synthesized Fe3O4-Pd50 catalyst could be recycled at least ten times with no significant loss of catalytic activity by external magnet separation.

Metal Ion Releasing Gold Nanoparticles for Improving Therapeutic Efficiency of Tumor Targeted Photothermal Therapy.

BACKGROUND: Owing to the tumor-targeted migration capacity of human mesenchymal stem cells (hMSCs), they have been combined with nanoparticles for photothermal therapy. However, the low viability of hMSCs following transplantation remains a problem. Here, we developed iron (Fe) ion-releasing gold (Au) nanoparticles (IIAuNPs) for advanced tumor-targeted photothermal therapy using hMSCs. METHODS: IIAuNPs were designed to undergo degradation under low pH conditions, such as the endosomal microenvironment, for Fe ion release in hMSCs. After evaluating the properties of IIAuNP, the IIAuNP concentration for treating hMSCs was optimized in terms of cytotoxicity. In vitro cell migration and antiapoptotic factor secretion were observed in hMSCs. Additionally, IIAuNPs-treated hMSCs were intravenously injected into tumor-bearing mice, and enhanced tumor targeting based on improved cell viability and cell migration was evaluated. Three days after the injection, the mice were irradiated with 660 nm laser to confirm the enhanced photothermal effect. RESULTS: In vitro studies revealed that treating hMSCs with an optimum concentration of IIAuNPs enhanced cell migration and anti-apoptotic gene expression through intracellular Fe ion delivery. The viability of hMSCs under hypoxic cell culture conditions that mimic the in vivo microenvironment was also improved when hMSCs were treated with IIAuNPs, compared to hMSCs without IIAuNPs treatment. IIAuNPs-treated hMSCs showed significantly enhanced tumor-targeting efficiency and subsequent photothermal effect compared to hMSCs without IIAuNP treatment. CONCLUSION: Our results suggest that our metal-ion-releasing photothermal nanoparticles may provide a promising platform for future photothermal therapies and related applications.

Three-in-One Strategy to Improve Both Catalytic Activity and Selectivity: Nonconcentric Pd-Au Nanoparticles.

In direct H2O2 synthesis, the Pd-Au alloy was considered as a potential catalyst because of its much better performance compared to the prototype Pd; unfortunately, achieving both high activity and selectivity remains a challenge. Here, we synthesized nonconcentric Pd-Au NPs in which Au domain shells are formed only partially on Pd domain cores and tested them for direct H2O2 synthesis. It has three exposed regions of Pd, Au domains, and Pd-Au interfaces in a single NP (hence, a 3-in-1 strategy). Creating nonconcentric forms was demonstrated convincingly by density functional theory calculations. The nonconcentric Pd-Au particles exhibit high and well-balanced performances that are hard to achieve with traditional alloyed Pd-Au. The number of Pd/Au interfaces was found to be the key factor and thus was optimized by controlling the Au precursor concentrations. The hitherto underutilized structure of nonconcentric bimetallic alloys can be useful and thus should be more actively investigated for catalyst development.

Anti-senescence ion-delivering nanocarrier for recovering therapeutic properties of long-term-cultured human adipose-derived stem cells.

BACKGROUND: Human adipose-derived stem cells (hADSCs) have been used in various fields of tissue engineering because of their promising therapeutic efficacy. However, the stemness of hADSCs cannot be maintained for long durations, and their therapeutic cellular functions, such as paracrine factor secretion decrease during long-term cell culture. To facilitate the use of long-term-cultured hADSCs (L-ADSCs), we designed a novel therapeutic anti-senescence ion-delivering nanocarrier (AIN) that is capable of recovering the therapeutic properties of L-ADSCs. In the present study, we introduced a low-pH-responsive ion nanocarrier capable of delivering transition metal ions that can enhance angiogenic paracrine factor secretion from L-ADSCs. The AINs were delivered to L-ADSCs in an intracellular manner through endocytosis. RESULTS: Low pH conditions within the endosomes induced the release of transition metal ions (Fe) into the L-ADSCs that in turn caused a mild elevation in the levels of reactive oxygen species (ROS). This mild elevation in ROS levels induced a downregulation of senescence-related gene expression and an upregulation of stemness-related gene expression. The angiogenic paracrine factor secretion from L-ADSCs was significantly enhanced, and this was evidenced by the observed therapeutic efficacy in response to treatment of a wound-closing mouse model with conditioned medium obtained from AIN-treated L-ADSCs that was similar to that observed in response to treatment with short-term-cultured adipose-derived stem cells. CONCLUSIONS: This study suggests a novel method and strategy for cell-based tissue regeneration that can overcome the limitations of the low stemness and therapeutic efficacy of stem cells that occurs during long-term cell culture.

Development of pH-Responsive Polymer Coating as an Alternative to Enzyme-Based Stem Cell Dissociation for Cell Therapy.

Cell therapy usually accompanies cell detachment as an essential process in cell culture and cell collection for transplantation. However, conventional methods based on enzymatic cell detachment can cause cellular damage including cell death and senescence during the routine cell detaching step due to an inappropriate handing. The aim of the current study is to apply the pH-responsive degradation property of poly (amino ester) to the surface of a cell culture dish to provide a simple and easy alternative method for cell detachment that can substitute the conventional enzyme treatment. In this study, poly (amino ester) was modified (cell detachable polymer, CDP) to show appropriate pH-responsive degradation under mild acidic conditions (0.05% (w/v) CDP, pH 6.0) to detach stem cells (human adipose tissue-derived stem cells (hADSCs)) perfectly within a short period (less than 10 min). Compared to conventional enzymatic cell detachment, hADSCs cultured on and detached from a CDP-coated cell culture dish showed similar cellular properties. We further performed in vivo experiments on a mouse hindlimb ischemia model (1.0 × 106 cells per limb). The in vivo results indicated that hADSCs retrieved from normal cell culture dishes and CDP-coated cell culture dishes showed analogous therapeutic angiogenesis. In conclusion, CDP could be applied to a pH-responsive cell detachment system as a simple and easy nonenzymatic method for stem cell culture and various cell therapies.

Dual Ion Releasing Nanoparticles for Modulating Osteogenic Cellular Microenvironment of Human Mesenchymal Stem Cells.

In this study we developed a dual therapeutic metal ion-releasing nanoparticle for advanced osteogenic differentiation of stem cells. In order to enhance the osteogenic differentiation of human mesenchymal stem cells (hMSCs) and induce angiogenesis, zinc (Zn) and iron (Fe) were synthesized together into a nanoparticle with a pH-sensitive degradation property. Zn and Fe were loaded within the nanoparticles to promote early osteogenic gene expression and to induce angiogenic paracrine factor secretion for hMSCs. In vitro studies revealed that treating an optimized concentration of our zinc-based iron oxide nanoparticles to hMSCs delivered Zn and Fe ion in a controlled release manner and supported osteogenic gene expression (RUNX2 and alkaline phosphatase) with improved vascular endothelial growth factor secretion. Simultaneous intracellular release of Zn and Fe ions through the endocytosis of the nanoparticles further modulated the mild reactive oxygen species generation level in hMSCs without cytotoxicity and thus improved the osteogenic capacity of the stem cells. Current results suggest that our dual ion releasing nanoparticles might provide a promising platform for future biomedical applications.

Regulation of intracellular transition metal ion level with a pH-sensitive inorganic nanocluster to improve therapeutic angiogenesis by enriching conditioned medium retrieved from human adipose derived stem cells.

Cell therapy based on human adipose derived stem cells (hADSCs) is a known potential therapeutic approach to induce angiogenesis in ischemic diseases. However, the therapeutic efficacy of direct hADSC injection is limited by a low cell viability and poor cell engraftment after administration. To improve the outcomes of this kind of approach, various types of nanoparticles have been utilized to improve the therapeutic efficacy of hADSC transplantation. Despite their advantages, the adverse effects of nanoparticles, such as genetic damage and potential oncogenesis based on non-degradable property of nanoparticles prohibit the application of nanoparticles toward the clinical applications. Herein, we designed a transition metal based inorganic nanocluster able of pH-selective degradation (ps-TNC), with the aim of enhancing an hADSC based treatment of mouse hindlimb ischemia. Our ps-TNC was designed to undergo degradation at low pH conditions, thus releasing metal ions only after endocytosis, in the endosome. To eliminate the limitations of both conventional hADSC injection and non-degradable property of nanoparticles, we have collected conditioned medium (CM) from the ps-TNC treated hADSCs and administrated it to the ischemic lesions. We found that intracellular increment of transition metal ion upregulated the hypoxia-inducible factor 1α, which can induce vascular endothelial growth factor (VEGF) and basic fibroblast growth factor (bFGF) expressions. Based on the molecular mechanism, the secretion of VEGF and bFGF by ps-TNC treated hADSCs showed a significant improvement compared to that of untreated cells. Injecting the CM collected from ps-TNC treated hADSCs into the mouse hindlimb ischemia model (ps-TNC-CM group) showed significantly improved angiogenesis in the lesions, with improved limb salvage and decreased muscle degeneration compared to the group injected with CM collected from normal hADSCs (CM group). This study suggests a novel strategy, combining a known angiogenesis molecular mechanism with both an improvement on conventional stem cell therapy and the circumvention of some limitations still present in modern approaches based on nanoparticles.

Versatile Yolk-Shell Encapsulation: Catalytic, Photothermal, and Sensing Demonstration.

Here, a novel, versatile synthetic strategy to fabricate a yolk-shell structured material that can encapsulate virtually any functional noble metal or metal oxide nanocatalysts of any morphology in a free suspension fashion is reported. This strategy also enables encapsulation of more than one type of nanoparticle inside a single shell, including paramagnetic iron oxide used for magnetic separation. The mesoporous organosilica shell provides efficient mass transfer of small target molecules, while serving as a size exclusion barrier for larger interfering molecules. Major structural and functional advantages of this material design are demonstrated by performing three proof-of-concept applications. First, effective encapsulation of plasmonic gold nanospheres for localized photothermal heating and heat-driven reaction inside the shell is shown. Second, hydrogenation catalysis is demonstrated under spatial confinement driven by palladium nanocubes. Finally, the surface-enhanced Raman spectroscopic detection of model pollutant by gold nanorods is presented for highly sensitive environmental sensing with size exclusion.

Centrifugal microfluidic device for the high-throughput synthesis of Pd@AuPt core-shell nanoparticles to evaluate the performance of hydrogen peroxide generation.

We propose a novel high-throughput screening platform using a centrifugal microfluidic device for producing combinatorial tri-metallic catalysts. The centrifugal device was designed to perform 60 reactions under different conditions on a single device. As a model to search for an optimal tri-metallic catalyst, we synthesized a variety of Pd@AuPt nanoparticles (NPs), in which Pd nanocubes served as a core, and Au and Pt atoms formed a shell. The centrifugal microfluidic device was etched on the top and bottom sides, in which two zigzag-shaped microchannels were patterned on the top side, and 60 reaction chambers were fabricated on the bottom side. Through the sophisticated zigzag-shaped microchannels, Pt2+ ion and Pd nanocube solutions were injected into the channel in one shot, and the centrifugal force equally and automatically divided the injected solutions into 60 aliquots during the rotation. By controlling the sophisticated channel dimensions and designing the passive valve structure, the Pt2+ ion, Pd nanocube, and Au3+ solutions were loaded into the reaction chamber in sequential order depending on the programmed rotational direction and speed. Therefore, the ratio of Au to Pt to synthesize Pd@AuPt core-shell NPs was changed from 0.028 : 1 to 12 : 1, and accordingly, the resultant 60 types of Pd@AuPt catalysts presented with different ratios of metal atom compositions. Then, we screened the catalytic activity of the Pd@AuPt NPs for generating H2O2 according to the degree of coating of Au and Pt, and the Pd@AuPt catalyst with the Au/Pt ratio at 0.5 turned out to be the most effective.

Endosome-triggered ion-releasing nanoparticles as therapeutics to enhance the angiogenic efficacy of human mesenchymal stem cells.

Here, we report that Fe ions delivered into human mesenchymal stem cells (hMSCs) by bioreducible metal nanoparticles (NPs) enhance their angiogenic and cell-homing efficacy by controlling ion-triggered intracellular reactive oxygen species (ROS) and improve cell migration, while reducing cytotoxicity. Endosome-triggered iron-ion-releasing nanoparticles (ETIN) were designed to be low-pH responsive to take advantage of the low-pH conditions (4-5) of endosomes for in situ iron-ion release. Due to the different redox potentials of Fe and Au, only Fe could be ionized and released from our novel ETIN, while Au remained intact after ETIN endocytosis. Treatment with an optimal amount of ETIN led to a mild increase in intracellular ROS levels in hMSCs, which enhanced the expression of HIF-1α, a key trigger for angiogenic growth factor secretion from hMSCs. Treatmetn of hMSCs with ETIN significantly enhanced the expression of angiogenesis- and lesion-targeting-related genes and proteins. Transplantation of ETIN-treated hMSCs significantly enhanced angiogenesis and tissue regeneration in a wound-closing mouse model compared with those in untreated mice and mice that underwent conventional hMSC transplantation.

Facile Tailoring of Contact Layer Characteristics of the Triboelectric Nanogenerator Based on Portable Imprinting Device.

Renewable energy harvesting technologies have been actively studied in recent years for replacing rapidly depleting energies, such as coal and oil energy. Among these technologies, the triboelectric nanogenerator (TENG), which is operated by contact-electrification, is attracting close attention due to its high accessibility, light weight, high shape adaptability, and broad applications. The characteristics of the contact layer, where contact electrification phenomenon occurs, should be tailored to enhance the electrical output performance of TENG. In this study, a portable imprinting device is developed to fabricate TENG in one step by easily tailoring the characteristics of the polydimethylsiloxane (PDMS) contact layer, such as thickness and morphology of the surface structure. These characteristics are critical to determine the electrical output performance. All parts of the proposed device are 3D printed with high-strength polylactic acid. Thus, it has lightweight and easy customizable characteristics, which make the designed system portable. Furthermore, the finger tapping-driven TENG of tailored PDMS contact layer with microstructures is fabricated and easily generates 350 V of output voltage and 30 µA of output current with a simple finger tapping motion-related biomechanical energy.

Tailored Palladium-Platinum Nanoconcave Cubes as High Performance Catalysts for the Direct Synthesis of Hydrogen Peroxide.

To obtain high catalytic properties, finely modulating the electronic structure and active sites of catalysts is important. Herein, we report the design and economical synthesis of Pd@Pt core-shell nanoparticles for high productivity in the direct synthesis of hydrogen peroxide. Pd@Pt core-shell nanoparticles with a partially covered Pt shell on a Pd cube were synthesized using a simple direct seed-mediated growth method. The synthesized Pd@Pt core-shell nanoparticles were composed of high index faceted Pt on the corners and edges, while the Pd-Pt alloy was located on the terrace area of the Pd cubes. Because of the high-indexed Pt and Pd-Pt alloy sites, the synthesized concave Pd@Pt7 nanoparticles exhibited both high H2 conversion and H2O2 selectivity compared with Pd cubes.

Facile Aqueous-Phase Synthesis of Bimetallic (AgPt, AgPd, and CuPt) and Trimetallic (AgCuPt) Nanoparticles.

Multi-metallic nanoparticles continue to attract attention, due to their great potential in various applications. In this paper, we report a facile aqueous-phase synthesis for multi-metallic nanoparticles, including AgPt, AgPd, CuPt, and AgCuPt, by a co-reduction method within a short reaction time of 10 min. The atomic ratio of bimetallic nanoparticles was easily controlled by varying the ratio of each precursor. In addition, we found that AgCuPt trimetallic nanoparticles had a core-shell structure with an Ag core and CuPt shell.

Facile aqueous-phase synthesis of Ag-Cu-Pt-Pd quadrometallic nanoparticles.

Ag-Cu-Pt-Pd quadrometallic nanoparticles which small Pt and Pd nanoparticles were attached on the surface of AgCu Janus nanoparticles were firstly synthesized by sequential reduction of Pt and Pd precursor in the presence of Janus AgCu bimetallic nanoparticles as seeds in an aqueous solution. Even though there was a small amount of Cu2O on the surface, the synthesized nanoparticles were mainly composed of four independent metallic part, not alloy parts. By theoretical calculation and growth mechanism study, we found that different reducing rate between Ag+ and Cu2+ and sequential reduction of Pt and Pd precursors would be key roles for the formation of the quadrometallic nanoparticles.

Synthesis of Sub 3 nm-Sized Uniform Magnetite Nanoparticles Using Reverse Micelle Method for Biomedical Application.

We report a synthetic method for small and uniform Fe3O4 (magnetite) nanoparticles under mild conditions. Spherical sub-3 nm-sized magnetite nanoparticles were prepared via reverse micelles composed of oleylamine, F127, xylene, and water for the reaction of iron(III) stearate with hydrazine at a reaction temperature of 90 °C in air atmosphere. These synthesized magnetite nanoparticles exhibited good size uniformity. By controlling experimental conditions, we could easily control both size and size uniformity of these magnetite nanoparticles. We further investigated whether Fe3O4 could be used in biomedical applications. Cytotoxicity of Fe3O4 was evaluated with human adipose-derived stem cells (hADSCs). Our results showed that the number of hADSCs did not significantly decrease when these cells were treated with Fe3O4 nanoparticles at a concentration of up to 9 µg/mL. Apoptotic activity and cell proliferation of hADSCs treated with Fe3O4 nanoparticles were similar to those of hADSCs without any treatment. This novel method could be used for synthesizing uniform and biocompatible Fe3O4 nanoparticles with further biomedical applications.

Enhancing the Wound Healing Effect of Conditioned Medium Collected from Mesenchymal Stem Cells with High Passage Number Using Bioreducible Nanoparticles.

Injecting human mesenchymal stem cells (hMSCs) at wound sites is known to have a therapeutic effect; however, hMSCs have several limitations, such as low viability and poor engraftment after injection, as well as a potential risk of oncogenesis. The use of a conditioned medium (CM) was suggested as an alternative method for treating various wounds instead of direct hMSC administration. In addition to not having the adverse effects associated with hMSCs, a CM can be easily mass produced and can be stored for long-term, thereby making it useful for clinical applications. In general, a CM is collected from hMSCs with low passage number; whereas, the hMSCs with high passage number are usually discarded because of their low therapeutic efficacy as a result of reduced angiogenic factor secretion. Herein, we used a CM collected from high passage number (passage 12, P12) hMSCs treated with gold-iron nanoparticles (AuFe NPs). Our AuFe NPs were designed to release the iron ion intracellularly via endocytosis. Endosomes with low pH can dissolve iron from AuFe NPs, and thus, the intracellularly released iron ions up-regulate the hypoxia-inducible factor 1α and vascular endothelial growth factor (VEGF) expression. Through this mechanism, AuFe NPs improve the amount of VEGF expression from P12 hMSCs so that it is comparable to the amount of VEGF expression from low passage number (passage 6, P6), without treatment. Furthermore, we injected the CM retrieved from P12 MSCs treated with AuFe NPs in the mouse skin wound model (AuFe P12 group). AuFe P12 group revealed significantly enhanced angiogenesis in the mouse skin wound model compared to the high passage hMSC CM-injected group. Moreover, the result from the AuFe P12 group was similar to that of the low passage hMSC CM-injected group. Both the AuFe P12 group and low passage hMSC CM-injected group presented significantly enhanced re-epithelization, angiogenesis, and tissue remodeling compared to the high passage hMSC CM-injected group. This study reveals a new strategy for tissue regeneration based on CM injection without considering the high cell passage count.

Highly sensitive and selective visual detection of Cr(VI) ions based on etching of silver-coated gold nanorods.

We report a visual detection of Cr(VI) ions using silver-coated gold nanorods (AuNR@Ag) as sensing probes. Au NRs were prepared by a seed-mediated growth process and AuNR@Ag nanostructures were synthesized by growing Ag nanoshells on Au NRs. Successful coating of Ag nanoshells on the surface of Au NRs was demonstrated with TEM, EDS, and UV-vis spectrometer. By increasing the overall amount of the deposited Ag on Au NRs, the localized surface plasmon resonance (LSPR) band was significantly blue-shifted, which allowed tuning across the visible spectrum. The sensing mechanism relies on the redox reaction between Cr(VI) ions and Ag nanoshells on Au NRs. As the concentration of Cr(VI) ions increased, more significant red-shift of the longitudinal peak and intensity decrease of the transverse peak could be observed using UV-vis spectrometer. Several parameters such as concentration of CTAB, thickness of the Ag nanoshells and pH of the sample were carefully optimized to determine Cr(VI) ions. Under optimized condition, this method showed a low detection limit of 0.4 µM and high selectivity towards Cr(VI) over other metal ions, and the detection range of Cr(VI) was tuned by controlling thickness of the Ag nanoshells. From multiple evaluations in real sample, it is clear that this method is a promising Cr(VI) ion colorimetric sensor with rapid, sensitive, and selective sensing ability.