Shengmin Xu

Rapid Synthesis of Stable and Functional Conjugates of DNA/Gold Nanoparticles Mediated by Tween 80

Gold nanoparticles conjugated with DNA represent an attractive and alternative platform for broad applications in biosensors, medical diagnostic, and biological analysis. However, current methods to conjugate DNA to gold nanoparticles are time-consuming. In this study, we report a novel approach to rapidly conjugate DNA to gold nanoparticles (AuNPs) to form functional DNA/AuNPs in 2-3 h using Tween 80 as protective agent. With a fluorescence-based technique, we determine that the DNA density on the surface of AuNPs achieves about ∼60 strands per particles, which is comparable to the loading density in the current methods. Moreover, the DNA/AuNPs synthesized by our approach exhibit an excellent stability as a function of temperature, pH, and freeze-thaw cycle, and the functionality of DNA/AuNPs conjugates is also verified. The work presented here has important implications to develop the fast and reproducible synthesis of stable DNA-functionalized gold nanoparticles.

Insights into the Ecotoxicity of Silver Nanoparticles Transferred from Escherichia coli to Caenorhabditis elegans.

Previous studies have indicated that engineered nanomaterials can be transferred through the food chain. However, their potential ecotoxicity to the environment is not fully understood. Here, we systematically evaluated the physiological behavior and toxicity of polyvinylpyrrolidone (PVP)-coated silver nanoparticles (AgNPs) using a food chain model from Escherichia coli (E. coli) to Caenorhabditis elegans (C. elegans). Our results demonstrated that AgNPs accumulated in E. coli could be transferred to the C. elegans, and AgNPs were clearly distributed in the gut lumen, subcutaneous tissue and gonad. After being transferred to C. elegans through the food chain, the accumulated AgNPs caused serious toxicity to the higher trophic level (C. elegans), including effects on germ cell death, reproductive integrity and life span. Relative to larger particles (75 nm), small AgNPs (25 nm) more easily accumulated in the food chain and exhibited a stronger toxicity to the higher trophic level. More importantly, both the AgNPs that had accumulated in C. elegans through the food chain and the resulting impairment of germ cells could be transferred to the next generation, indicating that AgNP can cause genetic damage across generations. Our findings highlight that nanomaterials pose potential ecotoxicity to ecosystems via transport through the food chain.

Fluorescent G-quadruplex–NMM DNA probe for the detection of silver nanoparticles in aqueous media

This communication reports the development of a new homogeneous assay based on G-quadruplexes (G-DNA) and N-methylmesoporphyrin IX (NMM) for the sensitive and selective detection of silver nanoparticles.

Effects of ionic strength on physicochemical properties and toxicity of silver nanoparticles

In the environment, silver nanoparticles (AgNPs) undergo a number of potential transformations, such as aggregation, dissolution, and redox reactions. However, the transformation in ionic strength condition, as well as their related toxicity was not quite clear, especially in the in vivo system. In the present study, we comprehensively evaluated three different characteristics (ddH2O, EPA water and K+ medium (KM)) mediated changes in the physical morphology of AgNPs and the alteration of the toxicity to Caenorhabditis elegans (C. elegans). Our results showed besides the changes of AgNPs behavior such as the transformation of morphological, with the transmission electron microscopy we found for the first time that smaller nanoparticles (<5 nm) appeared around the pristine AgNPs after incubation in EPA or KM for 5 days. Together with these changes, the toxicity of AgNPs to C. elegans changed significantly, showing that a higher ionic strength medium resulted in greater toxicity to C. elegans, as measured by germ cell apoptosis, brood size and lifespan. More importantly, our results indicated that the higher toxicity of AgNPs to C. elegans reproduction was probably related to the appearance of the smaller-size AgNPs in higher ionic strength media. These findings highlight that toxicity assessments for the release of nanomaterial to the environment need to be improved to assess environmental safety more accurately.

Investigating the environmental factors affecting the toxicity of silver nanoparticles in Escherichia coli with dual fluorescence analysis

Flow cytometric investigation of the toxic effects of nanoparticles on bacteria is highly challenging and not sensitive due to the interference of aggregated nanoparticles: aggregated nanoparticles and bacteria are similar in size. In this study, an optimized dual fluorescence flow cytometric analysis was developed using PI-Lac::GFP (propidium iodide stained Escherichia coli (lac::GFP)) to monitor the toxicity of silver nanoparticles (AgNPs). As compared with single fluorescence analysis, the dual fluorescence analysis enabled more accurate evaluation of the toxic effects of AgNPs. We used this dual fluorescence analysis to investigate how AgNPs toxicity was affected by two typical environmental factors, divalent metal ions and surfactants. Our data revealed that Cu(2+) and SDS significantly enhanced the toxicity of AgNPs in a dose-dependent manner. SDS enhanced the toxicity of both AgNPs and Ag(+) ions, whereas Cu(2+) increased the toxicity of AgNPs but not dissolved Ag(+) ions. Our results suggest that this dual fluorescence analysis can be used to evaluate the toxicity of AgNPs accurately and sensitively.

Graphene oxide regulates cox2 in human embryonic kidney 293T cells via epigenetic mechanisms: dynamic chromosomal interactions

Abstract To extend the applications of engineered nanomaterials, such as graphene oxide (GO), it is necessary to minimize cytotoxicity. However, the mechanisms underlying this cytotoxicity are unclear. Dynamic chromosomal interactions have been used to illustrate the molecular bases of gene expression, which offers a more sensitive and cutting-edge technology to elucidate complex biological processes associated with epigenetic regulations. In this study, the role of GO-triggered chromatin interactions in the activation of cox2, a hallmark of inflammation, was investigated in normal human cells. Using chromosome conformation capture technology, we showed that GO triggers physical interactions between the downstream enhancer and the cox2 promoter in human embryonic kidney 293T (293T) via p65 and p300 complex-mediated dynamic chromatin looping, which was required for high cox2 expression. Moreover, tumor necrosis factor-α (TNF-α), located upstream of the p65 signaling pathway, contributed to the regulation of cox2 activation through dynamic chromatin architecture. Compared with pristine GO and aminated GO (GO-NH2), poly (acrylic acid)-functionalized GO (GO-PAA) induced a weaker inflammatory response and a weaker effect on chromatin architecture. Our results mechanistically link GO-mediated chromatin interactions with the regulation of cox2 and suggest that GO derivatives may minimize toxicity in practical applications.

Effect of ionic strength on bioaccumulation and toxicity of silver nanoparticles in Caenorhabditis elegans

The behavior of silver nanoparticles (AgNPs) is influenced by environmental factors which altered their bioaccumulation and toxicity. In this study, we comprehensively investigated the influence of ionic strength on the ecotoxicity of AgNPs to Caenorhabditis elegans (C. elegans) through the transfer from Escherichia coli (E. coli). Three different exposure media (deionized water, EPA water and KM) were used to pretreat AgNPs. E. coli was then exposed to these transformed AgNPs and fed to C. elegans. Our results indicated that ionic strength significantly enhanced the reproductive toxicity (germ cell corpses, brood size and lifespan) and neurotoxicity (head trash and body bend) of AgNPs in C. elegans. Moreover, ICP-MS analysis showed that higher ionic strength increased bioaccumulation of AgNPs in E. coli and the resulting Ag body burden of E. coli affected the transfer of AgNPs to C. elegans, which might be responsible for the increased toxicity to nematodes. Furthermore, we also found that the reactive oxygen species (ROS) level in C. elegans was significantly increased after exposed to E. coli contaminated with ionic strength-treated AgNPs, which might play another important role for the enhanced toxicity of AgNPs. Overall, this study showed that the bioavailability and potential ecotoxicity of AgNPs are associated with the environmental factors.

Involvement of telomerase activity inhibition and telomere dysfunction in silver nanoparticles anticancer effects

AIM To investigate the possible mechanisms of telomerase and telomere underlying the anticancer effects of silver nanoparticles (AgNPs). MATERIALS & METHODS 25nm polyvinylpyrrolidone-coated AgNPs were used. The telomerase activity and telomere function were evaluated. The anticancer effects of AgNPs were gauged with cell viability assay under different statement of telomerase and telomere. RESULTS & CONCLUSION AgNPs could inhibit telomerase activity and lead to telomere shortening and dysfunction. Overexpression of telomerase attenuated the anticancer activity of AgNPs, whereas downregulation of telomerase activity or dysfunction of the telomere enhanced the cytotoxicity of AgNPs in HeLa cells. Our findings provided strong evidence that the anticancer effects of AgNPs were mediated via interference with the telomerase/telomere.

Assessment of Genotoxic Effects by Constructing a 3D Cellular System with Highly Sensitive Mutagenic Human–Hamster Hybrid Cells

Owing to complex microenvironmental conditions, it is challenging to reflect the actual biological responses of tissues or the body in a two-dimensional (2D) cellular system. In the present study, a low-attachment-cultivation technique was employed to establish a highly sensitive 3D human-hamster hybrid (AL) model to study the mutagenic effects of environmental pollutants. The results showed that the established 3D system has apparent organizational characteristics. The average diameter and average cell number of the 3D cells were approximately 240 μm and 1500, respectively. The expression of stemness and cell-junction genes (biomarkers for 3D cells) was higher than that in 2D cells. The present study analyzed the mutagenic effects of the environmental carcinogens arsenite and silver nanoparticles using the established 3D system to demonstrate its efficiency in mutagenic assessment. The results showed that the mutagenic effects of arsenite (10 μM) and silver nanoparticles (10 μg/mL) were 70 ± 3 and 99 ± 7 per 105 survivors, respectively. These values were much lower than those from 2D AL cells and comparable to those from the in vivo system. These results suggest that the developed 3D-cell-culture model based on the 2D AL cellular system more effectively reflects the actual gene-mutation frequency of mutagens in vivo.

Assessment of the cytotoxic and mutagenic potential of the Jialu River and adjacent groundwater using human-hamster hybrid cells

The Jialu River in China has been seriously polluted by the direct discharge of industrial and domestic wastewater. The predominant contaminants of the Jialu River and its adjacent groundwater were recently investigated. However, the potential genotoxic impact of polluted water on human health remains to be clarified. Here, we used human-hamster hybrid (AL) cells, which are sensitive for detecting environmental mutagens. We found that the cytotoxicity and mutagenicity of the groundwater in the Jialu River basin were influenced by the infiltration of the Jialu River. Hydrological periods significantly affected the cytotoxicity, but not the mutagenic potential, of surface and groundwater. Further, the mutagenic potential of groundwater samples located <1km from the Jialu River (SM-2 water samples) was detected earlier than that of groundwater samples located approximately 20km from the Jialu River (SN water samples). Because of high cytotoxicity, the mutagenic potential of water samples from the Jialu River (SM-1 water samples) was not significantly enhanced compared with that of untreated controls. To further assess the mutagenic dispersion potential, an artificial neural network model was adopted. The results showed that the highest mutagenic potential of groundwater was observed approximately 10km from the Jialu River. Although further investigation of mutagenic spatial dispersion is required, our data are significant for advancing our understanding of the origin, dispersion, and biological effects of water samples from polluted areas.