Bio-mediated silver nanoparticle synthesis: mechanism and microbial inactivation

Even though plenty of literature is available on the biosynthesis of metal nanoparticles, there are serious lacunae on the mechanisms of their formation. In the present study, the mechanism of formation of mono-crystalline silver nanoparticles using a fruit extract of the ornamental tree Thevetia peruviana is emphasized, i.e. how the pH of the reaction mixture affected reaction kinetics and size of the nanoparticles. The facilitation of formation of Ag₂O at higher pH resulted in a faster rate of particle formation. The diameter of the bare particles at neutral pH determined by field emission scanning electron microscopy and the hydrodynamic diameter determined by dynamic light scattering were 53 and 104 nm, respectively. The silver nanoparticles exhibited good inactivation of Escherichia coli due to participation of free radicals as evidenced by electron spin resonance spectroscopy.     

Determination of the mechanism of photoinduced toxicity of selected metal oxide nanoparticles (ZnO, CuO, Co3O4 and TiO2) to E. coli bacteria

Cytotoxicity of selected metal oxide nanoparticles(MNPs)(ZnO,CuO,Co 3 O 4 and TiO 2)was investigated in Escherichia coli both under light and dark conditions.Cytotoxicity experiments were conducted with spread plate counting and the LC 50 values were calculated.We determined the mechanism of toxicity via measurements of oxidative stress,reduced glutathione,lipid peroxidation,and metal ions.The overall ranking of the LC 50 values was in the order of ZnO < CuO < Co 3 O 4 < TiO 2 under dark condition and ZnO < CuO < TiO 2 < Co 3 O 4 under light condition.ZnO MNPs were the most toxic among the tested nanoparticles.Our results indicate depletion of reduced glutathione level and elevation of malondialdehyde level correlated with the increase in oxidative stress.Released metal ions were found to have partial effect on the toxicity of MNPs to E.coli.In summary,the dynamic interactions of multiple mechanisms lead to the toxicity of the tested MNPs to E.coli.     

A mechanistic study of ciprofloxacin adsorption by goethite in the presence of silver and titanium dioxide nanoparticles

The adsorption behaviors of ciprofloxacin (CIP), a fluoroquinolone antibiotic, onto goethite (Gt) in the presence of silver and titanium dioxide nanoparticles (AgNPs and TiO₂NPs) were investigated. Results showed that CIP adsorption kinetics in Gt with or without NPs both followed the pseudo-second-order kinetic model. The presence of AgNPs or TiO₂NPs inhibited the adsorption of CIP by Gt. The amount of inhibition of CIP sorption due to AgNPs was decreased with an increase of solution pH from 5.0 to 9.0. In contrast, in the presence of TiO₂NPs, CIP adsorption by Gt was almost unchanged at pHs of 5.0∼6.5 but was decreased with an increase of pH from 6.5 to 9.0. The mechanisms of AgNPs and TiO₂NPs in inhibiting CIP adsorption by Gt were different, which was attributed to citrate coating of AgNPs resulting in competition with CIP for adsorption sites on Gt, while TiO₂NPs could compete with Gt for CIP adsorption. Additionally, CIP was adsorbed by Gt or TiO₂NPs through a tridentate complex involving the bidentate inner-sphere coordination of the deprotonated carboxylic group and hydrogen bonding through the adjacent carbonyl group on the quinoline ring. These findings advance our understanding of the environmental behavior and fate of fluoroquinolone antibiotics in the presence of NPs.     

单层硅烷负载磁铁矿纳米颗粒的制备及除磷性能

研究了N-氨乙基-γ-氨丙基三甲氧基硅烷在水溶液中以单层形式负载于磁铁矿纳米颗粒表面的方法,并研究了单分子层硅烷负载磁铁矿纳米颗粒吸附剂(monolayer of silane on magnetite nanoparticles,MSMNPs)的除磷性能.结果表明,在低浓度下(平衡浓度小于300 mg·L~(-1))硅烷在磁铁矿纳米颗粒表面产生单层吸附,而反应温度90℃以上或离子强度0.1 mol·L~(-1)NaCl以上可以使单层硅烷在磁铁矿纳米颗粒表面的覆盖度达到~100%.FTIR和XPS图谱显示负载的硅烷以化学键的形式与磁铁矿纳米颗粒表面相结合.单层硅烷负载不引起磁性强度的明显变化.MSMNPs对磷的吸附等温线更符合Langmuir模型,拟合得到的最大吸附量为7.59 mg·g~(-1).由于磷吸附位位于MSMNPs的最外面,磷的吸附及脱附均很快,30 min内达到90%以上,1 h内达到平衡.因此,MSMNPs是一种易分离因而可反复使用,并且可快速吸附与脱附污染物的新型吸附剂.     

Applications of magnetic nanoparticles in surface-enhanced Raman scattering (SERS) detection of environmental pollutants

Environmental pollution, a major problem worldwide, poses considerable threat to human health and ecological environment. Efficient and reliable detection technologies, which focus on the appearance of emerging environmental and trace pollutants, are urgently needed. Surface-enhanced Raman scattering(SERS) has become an attractive analytical tool for sensing trace targets in environmental field because of its inherent molecular fingerprint specificity and high sensitivity. In this review, we focused on the recent developments in the integration of magnetic nanoparticles(MNPs) with SERS for facilitating sensitive detection of environmental pollutants. An overview and classification of different types of MNPs for SERS detection were initially provided, enabling us to categorize the huge amount of literature that was available in the interdisciplinary research field of MNPs based SERS technology. Then, the basic working principles and applications of MNPs in SERS detection were presented. Subsequently, the detection technologies integrating MNPs with SERS that eventually were used for the detection of various environmental pollutions were reviewed. Finally, the advantages of MNP-basedSERS detection technology for environmental pollutants were concluded, and the current challenges and future outlook of this technology in practical applications were highlighted. The application of the MNPsbasedSERS techniques for environmental analysis will be significantly advanced with the great progresses of the nanotechnologies, optics, and materials.     

Synthesis, characterization and application of Lagerstroemia speciosa embedded magnetic nanoparticle for Cr(VI) adsorption from aqueous solution

Lagerstroemia speciosa bark (LB) embedded magnetic nanoparticles were prepared by co-precipitation of Fe²⁺ and Fe³⁺ salt solution with ammonia and LB for Cr(VI) removal from aqueous solution. The native LB, magnetic nanoparticle (MNP), L. speciosa embedded magnetic nanoparticle (MNPLB) and Cr(VI) adsorbed MNPLB particles were characterized by SEM–EDX, TEM, BET-surface area, FT-IR, XRD and TGA methods. TEM analysis confirmed nearly spherical shape of MNP with an average diameter of 8.76 nm and the surface modification did not result in the phase change of MNP as established by XRD analysis, while led to the formation of secondary particles of MNPLB with diameter of 18.54 nm. Characterization results revealed covalent binding between the hydroxyl group of MNP and carboxyl group of LB particles and further confirmed its physico-chemical nature favorable for Cr(VI) adsorption. The Cr(VI) adsorption on to MNPLB particle as an adsorbent was tested under different contact time, initial Cr(VI) concentration, adsorbent dose, initial pH, temperature and agitation speed. The results of the equilibrium and kinetics of adsorption were well described by Langmuir isotherm and pseudo-second-order model, respectively. The thermodynamic parameters suggest spontaneous and endothermic nature of Cr(VI) adsorption onto MNPLB. The maximum adsorption capacity for MNPLB was calculated to be 434.78 mg/g and these particles even after Cr(VI) adsorption were collected effortlessly from the aqueous solution by a magnet. The desorption of Cr(VI)-adsorbed MNPLB was found to be more than 93.72% with spent MNPLB depicting eleven successive adsorption–desorption cycles.     

Green synthesis, characterization and antimicrobial activity of silver nanoparticles using methanolic root extracts of Diospyros sylvatica

The current research study focuses to formulate the biosynthesized silver nanoparticles for the first time from silver acetate using methanolic root extracts of Diospyros sylvatica, a member of family Ebenaceae. TEM analysis revealed the average diameter of Ag NPs around 8 nm which is in good agreement with the average crystallite size (10 nm) calculated from X-ray Diffraction (XRD) analysis. Further the study has been extended to the antimicrobial activity against test pathogenic Gram (+) ve, Gram (−) ve bacterial and fungal strains. The bioinspired Ag-NP showed promising activity against all the tested bacterial strains and the activity was enhanced with increased dosage levels.     

Bioaccumulation and effects of sediment-associated gold- and graphene oxide nanoparticles on Tubifex tubifex

With the development of nanotechnology,gold(Au) and graphene oxide(GO) nanoparticles have been widely used in various fields,resulting in an increased release of these particles into the environment.The released nanoparticles may eventually accumulate in sediment,causing possible ecotoxicological effects to benthic invertebrates.However,the impact of Au-NPs and GO-NPs on the cosmopolitan oligochaete,Tubifex tubifex,in sediment exposure is not known.Mortality,behavioral impact(GO-NP and Au-NP) and uptake(only Au-NP) of sediment-associated Au-NPs(4.9±0.14 nm) and GO-NPs(116±0.05 nm) to T.tubifex were assessed in a number of 5-day exposure experiments.The results showed that the applied Au-NP concentrations(10 and 60 μg Au/g dry weight sediment) had no adverse effect on T.tubifex survival,while Au bioaccumulation increased with exposure concentration.In the case of GO-NPs,no mortality of T.tubifex was observed at a concentration range of 20 and180 μg GO/g dry weight sediment,whereas burrowing activity was significantly reduced at 20 and 180 μg GO/g dry weight sediment.Our results suggest that Au-NPs at 60 μg Au/g or GO-NPs at 20 and 180 μg GO/g were detected by T.tubifex as toxicants during short-term exposures.     

Complex interplay between formation routes and natural organic matter modification controls capabilities of C60 nanoparticles (nC60) to accumulate organic contaminants

Accumulation of organic contaminants on fullerene nanoparticles (nC₆₀) may significantly affect the risks of C₆₀ in the environment. The objective of this study was to further understand how the interplay of nC₆₀ formation routes and humic acid modification affects contaminant adsorption of nC₆₀. Specifically, adsorption of 1,2,4,5-tetrachlorobenzene (a model nonionic, hydrophobic organic contaminant) on nC₆₀ was greatly affected by nC₆₀ formation route – the formation route significantly affected the aggregation properties of nC₆₀, thus affecting the available surface area and the extent of adsorption via the pore-filling mechanism. Depending on whether nC₆₀ was formed via the “top-down” route (i.e., sonicating C₆₀ powder in aqueous solution) or “bottom-up” route (i.e., phase transfer from an organic solvent) and the type of solvent involved (toluene versus tetrahydrofuran), modification of nC₆₀ with Suwannee River humic acid (SRHA) could either enhance or inhibit the adsorption affinity of nC₆₀. The net effect depended on the specific way in which SRHA interacted with C₆₀ monomers and/or C₆₀ aggregates of different sizes and morphology, which determined the relative importance of enhanced adsorption from SRHA modification via preventing C₆₀ aggregation and inhibited adsorption through blocking available adsorption sites. The findings further demonstrate the complex mechanisms controlling interactions between nC₆₀ and organic contaminants, and may have significant implications for the life-cycle analysis and risk assessment of C₆₀.     

斑马鱼在纳米金属及金属氧化物毒性研究中的应用

纳米金属及金属氧化物材料在催化、涂料、电子、机械和生物医学领域大量生产和应用,因此,对纳米金属材料及其氧化物可能给环境以及人体健康带来的潜在影响和风险需要有足够的认识.本文就近年来纳米金属及金属氧化物对斑马鱼毒性的研究进展进行综述,为人们进一步认识和更好地应用纳米材料奠定基础.