Potential Toxicity of Up-Converting Nanoparticles Encapsulated with a Bilayer Formed by Ligand Attraction

The cellular toxicity of nanoparticles that were capped with a bilayered ligand was studied using an up-converting (UC) phosphor material as a representative nanoparticle (NP). The results indicate that although UC NPs are known to be nontoxic, the toxicity of the NPs depends strongly on ligand coordination conditions, in addition to the other commonly known parameters such as size, structure, surface charge etc. Oleate-capped hydrophobic NaYF₄:Yb,Er NPs were surface modified to yield three extreme conditions: bare particles that were stripped of the oleate ligands; particles with covalently bound poly­(ethylene glycol) (PEG) ligands; and particles with an bilayer of PEG-oleate ligands using the oleate surface group that was remained after synthesis. It was found that the bare particles and the covalent PEG NPs induced little toxicity. However, particles that were rendered biocompatible by forming a bilayer with an amphiphilic ligand (i.e., PEG-oleate) resulted in significant cell toxicity. These findings strongly suggest that the PEG-oleate group dissociated from the bilayered oleate-capped NPs, resulting in significant toxicity by exposing the hydrophobic oleate-capped NPs to the cell. Based on results with bare particles, the NaLnF₄:Yb,Er (Ln = Y, Gd) up-converting phosphors are essentially less-toxic. Capping and functionalizing these particles with ligand intercalation may, however, not be a suitable method for rendering the NPs suitable for bioapplication as the ligand can potentially dissociate upon cellular interaction, leading to significant toxicity

Characterization of CuO NP used in the present study.

<p>(A) Representative transmission electron microscopy (TEM) images of the CuO NP at two magnifications. The polydisperse size distribution of CuO NP (n = 245) determined from TEM images is shown in the insert. The average size of the NP is shown (mean ± <i>SD</i>). (B) X-Ray diffraction (XRD) pattern of the NP. The X, and Y axes of the XRD represents the angles (2θ) of incident X-ray beam and the corresponding diffraction peak intensity.</p

Sublethal Effects of CuO Nanoparticles on Mozambique Tilapia (<i>Oreochromis mossambicus</i>) Are Modulated by Environmental Salinity

<div><p>The increasing use of manufactured nanoparticles (NP) in different applications has triggered the need to understand their putative ecotoxicological effects in the environment. Copper oxide nanoparticles (CuO NP) are toxic, and induce oxidative stress and other pathophysiological conditions. The unique properties of NP can change depending on the characteristics of the media they are suspended in, altering the impact on their toxicity to aquatic organisms in different environments. Here, Mozambique tilapia (<i>O. mossambicus</i>) were exposed to flame synthesized CuO NP (0.5 and 5 mg·L⁻¹) in two environmental contexts: (a) constant freshwater (FW) and (b) stepwise increase in environmental salinity (SW). Sublethal effects of CuO NP were monitored and used to dermine exposure endpoints. Fish exposed to 5 mg·L⁻¹ CuO in SW showed an opercular ventilation rate increase, whereas fish exposed to 5 mg·L⁻¹ in FW showed a milder response. Different effects of CuO NP on antioxidant enzyme activities, accumulation of transcripts for metal-responsive genes, GSH∶GSSG ratio, and Cu content in fish gill and liver also demonstrate that additive osmotic stress modulates CuO NP toxicity. We conclude that the toxicity of CuO NP depends on the particular environmental context and that salinity is an important factor for modulating NP toxicity in fish.</p></div

Expression of metal-responsive genes.

<p>Transcripts levels analysis by qPCR in liver (black bars) and gills (white bars). Transcript accumulation of (<b>A</b>) <i>Cytochrome P450 1A</i> (<i>CYP1A</i>), and (<b>B</b>) <i>Metallothionein</i> (<i>MT</i>). The genes were analyzed by qPCR in gills and liver, and normalized as function of the levels of endogenous control <i>β-Actin</i> gene. FW0, fresh water; FW0.5, FW plus 0.5 mg·L⁻¹ CuO; FW5, FW plus 5 mg·L⁻¹ CuO; SW0, increasing salinity; SW0.5, SW plus 0.5 mg·L⁻¹ CuO; SW5, SW plus 5 mg·L⁻¹ CuO. Results expressed as percentage of relative quantification. Significant different means by Anova on ranks analysis are shown with ‡ (<i>P</i> value), and significant differences between FW-SW at the same CuO NP concentration (Dunn's post test, <i>P</i><0.05) are shown with §. Asterisks represent significant difference compared to the respective FW0 control by Wilcoxon Signed Rank test (*, <i>P</i><0.05; ** <i>P</i><0.025). <i>n</i>×treatment = 5.</p

Cu-content of liver and gills after CuO NP exposure at different salinities.

<p>Values (ng of Cu per mg of dry weight) are depicted as mean ± SEM. FW0, fresh water; FW0.5, FW plus 0.5 mg·L⁻¹ CuO; FW5, FW plus 5 mg·L⁻¹ CuO; SW0, increasing salinity; SW0.5, SW plus 0.5 mg·L⁻¹ CuO; SW5, SW plus 5 mg·L⁻¹ CuO. Significant different means by Anova analysis are shown with ‡ (<i>P</i> value). Letters denote groups showing non significant differences by Tukey's post-test (<i>P</i><0.05). <i>n</i>×treatment = 5.</p

Glutathione levels in livers and gills of CuO NP exposed fish in different salinities.

<p>Total glutathione (GSH+GSSG, top panel); Oxidized glutathione (GSSG) and reduced glutathione (GSH) levels (center panel). The ratio GSH/GSSH is shown in bottom panel. FW0, fresh water; FW0.5, FW plus 0.5 mg·L⁻¹ CuO; FW5, FW plus 5 mg·L⁻¹ CuO; SW0, increasing salinity; SW0.5, SW plus 0.5 mg·L⁻¹ CuO; SW5, SW plus 5 mg·L⁻¹ CuO. Expressed as mean nmol.mg tissue⁻¹ ± <i>SD</i>. Groups with significant different means by Anova analysis are shown with ‡ (<i>P</i> value). Letters denote groups showing non significant differences by Tukey's post-test (<i>P</i><0.05). <i>n</i>×treatment = 5.</p

Experimental conditions during CuO NP exposure.

<p>(<b>A</b>) Salinity changes regime for FW and SW tanks. The FW tanks were kept in constant freshwater (0.1 ppt, gray triangles), while in SW tanks, salinity was increased in a stepwise manner every day (black squares), by addition of increasing amounts of sea salt. Salinity increase steps were of 7 ppt/day, except for the first day when the increase was of 3 ppt. (<b>B</b>) Opercular ventilation rate (OVR) in experimental tanks, measured as opercular beats/minute and expressed as the daily mean per tank (n = 7). The dotted line represent the 25% increment selected as experimental end point. Asterisks denote significant differences relative to the FW0 per day (<i>P</i><0.05). Top: FW0, fresh water; FW0.5, FW plus 0.5 mg·L⁻¹ CuO; FW5, FW plus 5 mg·L⁻¹ CuO; Bottom: SW0, increasing salinity; SW0.5, SW plus 0.5 mg·L⁻¹ CuO; SW5, SW plus 5 mg·L⁻¹ CuO. <i>n</i>×tank = 7.</p

BET and Zeta Potential of CuO NP.

<p>(<b>A</b>) BET isotherm of the CuO NP (powder). (<b>B</b>) Zeta Potential (ZP) of the NP sample taken from FW5 tanks over the time. Day 0 represents the ZP of the NP right after mixing to the fresh water of the fish tank. The ZP of the NP remained fairly constant though out the experiments. The dotted line showed as a guide.</p

Ultrasensitive On-Chip Immunoassays with a Nanoparticle-Assembled Photonic Crystal

Electrophoretic particle entrapment system (EPES) is employed to generate 2D array of nanoparticles coated with biological molecules (<i>i.e.</i>, antibodies). Phase matching of the excitation and the emission in the 2D arrays with particles produces a highly enhanced fluorescence signal that was shown to improve the limit of detection in immunoassays. The phase matching is achieved when the particle are in the sub-100 nm range. A comparison between different size particles shows that the sensitivity of an immunoassay is extended to a range that is difficult to achieve with standard technology (<i>e.g.</i>, enzyme-linked immunosorbent assay-ELISA). The effectiveness of this novel configuration of particle-in-a-well was demonstrated with an assay for human epidermal growth factor receptor 2 (HER2; breast cancer biomarker), with a detection limit as low as 10 attomolar (aM) in less than 10 μL of serum-based sample. The limit of detection of HER2 indicated far superior assay performance compared to the corresponding standard 96-well plate-based ELISA. The particle-based photonic platform reduces the reagent volume and the time for performing an assay in comparison to competing methods. The simplicity of operation and the level of sensitivity demonstrated here can be used for rapid and early stage detection of biomarkers

Capture and Detection of T7 Bacteriophages on a Nanostructured Interface

A highly ordered array of T7 bacteriophages was created by the electrophoretic capture of phages onto a nanostructured array with wells that accommodated the phages. Electrophoresis of bacteriophages was achieved by applying a positive potential on an indium tin oxide electrode at the bottom of the nanowells. Nanoscale arrays of phages with different surface densities were obtained by changing the electric field applied to the bottom of the nanowells. The applied voltage was shown to be the critical factor in generating a well-ordered phage array. The number of wells occupied by a phage, and hence the concentration of phages in a sample solution, could be quantified by using a DNA intercalating dye that rapidly stains the T7 phage. The fluorescence signal was enhanced by the intrinsic photonic effect made available by the geometry of the platform. It was shown that the quantification of phages on the array was 6 orders of magnitude better than could be obtained with a fluorescent plate reader. The device opens up the possibility that phages can be detected directly without enrichment or culturing, and by detecting phages that specifically infect bacteria of interest, rapid pathogen detection becomes possible