Joachim Say Chye Loo

Copper molybdenum sulfide: a new efficient electrocatalyst for hydrogen production from water

A new inorganic solid state electrocatalyst for the hydrogen evolution reaction (HER) is reported. Highly crystalline layered ternary sulfide copper-molybdenum-sulfide (Cu2MoS4) was prepared by a simple precipitation method from CuI and [MoS4]2− precursors. In aqueous solution and over a wide pH range (pH 0 to 7), this Cu2MoS4 showed very good catalytic activity for HER with an overvoltage requirement of only ca. 135 mV and an apparent exchange current density of 0.040 mA cm−2 (Tafel slope of ca. 95 mV per decade was found irrespective of the pH value). This Cu2MoS4 catalyst was found to be stable during electrocatalytic hydrogen generation. Therefore, it represents an attractive alternative to platinum.

The role of the tumor suppressor p53 pathway in the cellular DNA damage response to zinc oxide nanoparticles.

In this paper, we explored how ZnO nanoparticles cross-interact with a critical tumor suppressive pathway centered around p53, which is one of the most important known tumor suppressors that protects cells from developing cancer phenotypes through its control over major pathways like apoptosis, senescence and cell cycle progression. We showed that the p53 pathway was activated in BJ cells (skin fibroblasts) upon ZnO nanoparticles treatment with a concomitant decrease in cell numbers. This suggests that cellular responses like apoptosis in the presence of ZnO nanoparticles require p53 as the molecular master switch towards programmed cell death. This also suggests that in cells without robust p53, protective response can be tipped towards carcinogenesis when stimulated by DNA damage inducing agents like ZnO nanoparticles. We observed this precarious tendency in the same BJ cells with p53 knocked down using endogeneous expressing shRNA. These p53 knocked down BJ cells became more resistant to ZnO nanoparticles induced cell death and increased cell progression. Collectively, our results suggest that cellular response towards specific nanoparticle induced cell toxicity and carcinogenesis is not only dependent on specific nanoparticle properties but also (perhaps more importantly) the endogenous genetic, transcriptomic and proteomic landscape of the target cells.

Gadolinium oxide ultranarrow nanorods as multimodal contrast agents for optical and magnetic resonance imaging.

We demonstrate a simple synthetic strategy for the fabrication of single-phase rare earth (RE) doped gadolinium oxide (Gd(2)O(3):RE where RE = terbium (Tb), ytterbium (Yb), and erbium (Er)) nanorods (NRs) as multimodal imaging probes. The NRs are ultranarrow and exhibit both emission and magnetic characteristics. The Tb-doped and Yb/Er-codoped Gd(2)O(3) NRs exhibit down- and up-conversion fluorescence respectively, and also exhibit paramagnetism. Importantly, these codoped NRs possess excellent magnetic characteristics, as shown in their longitudinal relaxation time (T1) -weighted image contrast, which is closer to that of commercial Gadovist for magnetic resonance imaging (MRI) applications. This property opens up new avenues in the development of contrast agents.

Toxicity of zinc oxide (ZnO) nanoparticles on human bronchial epithelial cells (BEAS-2B) is accentuated by oxidative stress.

Although several studies reported that cytotoxic effects of various nanoparticles are partially due to induction of oxidative stress, it is unclear how oxidative state of the cell per se could influence its sensitivity to cytotoxic nanoparticles. This is of clinical significance because certain pathological conditions such as inflammation is associated with elevated oxidative stress and this may alter sensitivity of cells and tissues to cytotoxic nanoparticles. Hence, this study investigated how initial exposure of BEAS-2B human bronchial epithelial cells to oxidative stress influences subsequent response to cytotoxic challenge with zinc oxide (ZnO) nanoparticles (approximately 10nm). Oxidative stress was induced by exposing BEAS-2B cells to 5 and 10 microM of H(2)O(2) for 45 min in PBS (with Ca(2+)). Subsequently, the H(2)O(2) solutions were washed off and the cells were exposed to varying concentrations (5-25 microg/ml) of ZnO nanoparticles in culture media for 24h, followed by cell viability assessment with the WST-8 assay. The results demonstrated that initial transient exposure of cells to oxidative stress accentuated cytotoxicity of ZnO nanoparticles. In the negative control unexposed to H(2)O(2), >99% of cells remained viable up to a ZnO nanoparticle concentration of 10 microg/ml, but displayed a steep decrease in viability above 10 microg/ml ZnO. By contrast, cells that were initially exposed to 5 and 10 microM of H(2)O(2), displayed a sharp drop in viability even at concentrations below 10 microg/ml ZnO. At 10 microg/ml ZnO, cells initially exposed to 10 microM H(2)O(2) displayed a viability of 40.6+/-2.0%, which is significantly lower than the corresponding values of 72.8+/-2.0% and 99.9+/-1.1% obtained for initial exposure to 5 microM H(2)O(2) and the negative control, respectively. Hence, initial exposure of BEAS-2B cells to oxidative stress sensitized their subsequent response to cytotoxic challenge with ZnO nanoparticles.

Nanostructure control of graphene-composited TiO2 by a one-step solvothermal approach for high performance dye-sensitized solar cells

We present a one-step solvothermal approach to prepare uniform graphene-TiO(2) nanocomposites with delicately controlled TiO(2) nanostructures, including ultra-small 2 nm nanoparticles, 12 nm nanoparticles and nanorods. Using three composites as photoanode materials, the effect of nanostructure of graphene-composited TiO(2) on the performance of dye-sensitized solar cells was investigated, and results showed that the ultra-small 2 nm TiO(2)-graphene composite based photoanode exhibited the highest power conversion efficiency of 7.25%.

Novel assembly of an MoS2 electrocatalyst onto a silicon nanowire array electrode to construct a photocathode composed of elements abundant on the Earth for hydrogen generation

Mild-mannered catalyst: a novel procedure to load a MoS(2) co-catalyst onto the surface of silicon under mild-conditions (room temperature, atmospheric pressure, aqueous solution) by a photo-assisted electrodeposition process employing commercially available precursors is reported. The obtained Si-NW@MoS(2) photocathode showed similar catalytic activity for light-driven H(2) generation compared with a Si-NW@Pt photocathode.

Adverse biophysical effects of hydroxyapatite nanoparticles on natural pulmonary surfactant.

Inhaled nanoparticles (NPs) must first interact with the pulmonary surfactant (PS) lining layer that covers the entire internal surface of the respiratory tract and plays an important role in surface tension reduction and host defense. Interactions with the PS film determine the subsequent clearance, retention, and translocation of the inhaled NPs and hence their potential toxicity. To date, little is known how NPs interact with PS, and whether or not NPs have adverse effects on the biophysical function of PS. We found a time-dependent toxicological effect of hydroxyapatite NPs (HA-NPs) on a natural PS, Infasurf, and the time scale of surfactant inhibition after particle exposure was comparable to the turnover period of surfactant metabolism. Using a variety of in vitro biophysicochemical characterization techniques, we have determined the inhibition mechanism to be due to protein adsorption onto the HA-NPs. Consequently, depletion of surfactant proteins from phospholipid vesicles caused conversion of original large vesicles into much smaller vesicles with poor surface activity. These small vesicles, in turn, inhibited biophysical function of surfactant films after adsorption at the air-water interface. Cytotoxicity study found that the HA-NPs at the studied concentration were benign to human bronchial epithelial cells, thereby highlighting the importance of evaluating biophysical effect of NPs on PS. The NP-PS interaction mechanism revealed by this study may not only provide new insight into the toxicological study of nanoparticles but also shed light on the feasibility of NP-based pulmonary drug delivery.

Exposure to Titanium Dioxide Nanoparticles Induces Autophagy in Primary Human Keratinocytes

Understanding the mechanisms of cell-nanomaterial interactions is vital in harnessing the potential of using nanomaterials in biomedical applications. By immuno-labeling of LC3 and TEM analysis, it is found that titanium dioxide nanoparticles are internalized by human keratinocytes and induce autophagy. Autophagy appears to play a cytoprotective role in response to toxicity influence exerted by the nanoparticles.

Rhodamine‐Modified Upconversion Nanophosphors for Ratiometric Detection of Hypochlorous Acid in Aqueous Solution and Living Cells

Hypochlorous acid (HOCl), a reactive oxygen species (ROS) produced by myeloperoxidase (MPO) enzyme-mediated peroxidation of chloride ions, acts as a key microbicidal agent in immune systems. However, misregulated production of HOCl could damage host tissues and cause many inflammation-related diseases. Due to its biological importance, many efforts have been focused on developing fluorescent probes to image HOCl in living system. Compared with those conventional fluorescent probes, up-conversion luminescence (UCL) detection system has been proven to exhibit a lot of advantages including no photo-bleaching, higher light penetration depth, no autofluorescence and less damage to biosamples. Herein, we report a novel water-soluble organic-nano detection system based on rhodamine-modified UCNPs for UCL-sensing HOCl. Upon the interaction with HOCl, the green UCL emission intensity in the detection system were gradually decreased, but the emissions in the NIR region almost have no change, which is very important for the ratiometric UCL detection of HOCl in aqueous solution. More importantly, RBH1-UCNPs could be used for the ratiometric UCL visualization of HOCl released by MPO-mediated peroxidation of chloride ions in living cells. This organic-nano system could be further developed into a novel next-generation imaging technique for bio-imaging HOCl in living system without background noise.

Cytotoxic and genotoxic characterization of titanium dioxide, gadolinium oxide, and poly(lactic-co-glycolic acid) nanoparticles in human fibroblasts†

Engineered nanomaterials have become prevalent in our everyday life. While the popularity of using nanomaterials in consumer products continues to rise, increasing awareness of nanotoxicology has also fuelled efforts to accelerate our understanding of the ill effects that different nanomaterials can bring to biological systems. In this study, we investigated the potential cytotoxicity and genotoxicity of three nanoparticles: titanium dioxide (TiO(2)), terbium-doped gadolinium oxide (Tb-Gd(2)O(3)), and poly(lactic-co-glycolic acid) (PLGA). To evaluate nanoparticle-induced genotoxicity more realistically, a human skin fibroblast cell line (BJ) with less mutated genotype compared with cancer cell line was used. The nanoparticles were first characterized by size, morphology, and surface charge. Cytotoxicity effects of the nanoparticles were then evaluated by monitoring the proliferation of treated BJ cells. Genotoxic influence was ascertained by profiling DNA damage via detection of γH2AX expression. Our results suggested that both TiO(2) and Tb-Gd(2)O(3) nanoparticles induced cytotoxicity in a dose dependent way on BJ cells. These two nanomaterials also promoted genotoxicity via DNA damage. On the contrary, PLGA nanoparticles did not induce significant cytotoxic or genotoxic effects on BJ cells.