Modifying and Fine Controlling of Silver Nanoparticle Nucleation Sites and SERS Performance by Double Silicon Etching Process

Different forms of modified and well-controlled plasmonic silver nanoparticles (AgNPs) were synthesized by silver ion reduction process of porous silicon (PS). Fine control of PS surface morphology was accomplished by employing two etching processes: light-induced etching (LIE) and photo electrochemical etching (PECE). The idea was to prepare excellent and reproducible surface-enhanced Raman scattering (SERS) substrates with high enhancement performance. PS surface modification was employed to create efficient and nearly uniformly distributed AgNP hotspot regions with very high specific surface areas. Reproducibility deviation of no more than 5% and enhancement factor of 1.2 × 10¹⁴ were obtained by SERS measurements at very low, rhodamine 6G (R6G) dye, concentration 10^?15 M. The PS morphology SERS substrate was well discussed and analyzed using field emission scanning electron microscopy (FE-SEM), X-ray diffraction spectroscopy (XRD), and Raman measurements.     

Tapered Fiber Probe Modified by Ag Nanoparticles for SERS Detection

A tapered optical fiber fabricated by a simple chemical etching method and modified with Ag nanoparticles (AgNPs) by chemical deposition was evaluated for surface-enhanced Raman scattering (SERS). The fiber probe was used for SERS measurements in both direct and remote scattering modes, yielding desired performance in both scattering configurations. The state of the obtained AgNPs made a significant contribution to the high sensitivity of SERS to Rhodamine 6G (R6G) molecules (down to a concentration of 10^?7 M), and the substrate had an analyst enhancement factor (AEF) on the order of ～10⁸. Meanwhile, the SERS intensity during the evaporation process was investigated, showing a good stability at the later stage of the evaporation process. The fiber SERS probes demonstrated good reproducibility with the average relative standard deviation (RSD) values being less than 0.2 for the major Raman peaks.     

Diagonally Aligned Squared Metal Nano-pillar with Increased Hotspot Density as a Highly Reproducible SERS Substrate

Metal nanostructure on dielectric substrate with increased hotspot density has drawn considerable research interest in recent years toward the study of surface-enhanced Raman spectroscopy (SERS). In this paper, we report the fabrication of a diagonally aligned squared metal nano-pillar (SMNP) on a dielectric substrate and revealed it as an efficient SERS substrate with increased hotspot density for sensing of Raman active materials. Due to dipolar coupling and lightening rod effect between the neighboring nano-pillars, the localized surface plasmon resonance (LSPR) field intensity increased significantly in the space between two neighboring SMNP which would lead to the enhancement of SERS signal. The SMNP has been fabricated using electron beam lithographic (EBL) technique with hotspot density of 2.45 × 10⁷/mm². With the designed SERS substrate an average enhancement factor (EF) of 3.27 × 10⁸ has been observed with relative standard deviation of ～13 %.     

Interaction of flavonols with human serum albumin: a biophysical study showing structure–activity relationship and enhancement when coated on silver nanoparticles

Binding affinities of flavonols namely quercetin, myricetin, and kaempferol to human serum albumin (HSA) were determined fluorimetrically and the order was observed to be myricetin > quercetin > kaempferol demonstrating structure–activity relationship. Quercetin-coated silver nanoparticles (AgNPs) show higher binding affinity to HSA compared to free quercetin with binding constants 6.04 × 10⁷ M^?1 and 4.2 × 10⁶ M^?1, respectively. Using site-specific markers it is concluded that free quercetin and that coated on AgNPs bind at different sites. Significant structural changes in circular dichroism (CD) spectra of HSA were recorded with quercetin-coated AgNPs compared to free quercetin. These results were further substantiated by time-resolved fluorescence spectroscopy where fluorescence life time of the tryptophan residue in HSA–quercetin-coated AgNPs complex decreased to 3.63 ns from 4.22 ns in HSA–quercetin complex. Isothermal calorimetric studies reveal two binding modes for quercetin-coated AgNPs and also higher binding constants compared to free quercetin. These higher binding affinities are attributed to altered properties of quercetin when coated on AgNPs enabling it to reach the binding sites other than site II where free quercetin mainly binds.     

Preparation,characterization of silver phyto nanoparticles and their impact on growth potential of Lupinus termis L. seedlings

The current study reports rapid and easy method for synthesis of eco-friendly silver nanoparticles (AgNPs) using Coriandrum sativum leaves extract as a reducing and covering agent. The bio-reductive synthesis of AgNPs was monitored using a scanning double beam UV-vis spectrophotometer. Transmission electron microscopy (TEM) was used to characterize the morphology of AgNPs obtained from plant extracts. X-ray diffraction (XRD) patterns of AgNPs indicate that the structure of AgNPs is the face centered cubic structure of metallic silver. The surface morphology and topography of the AgNPs were examined by scanning electron microscopy and the energy dispersive spectrum revealed the presence of elemental silver in the sample. The silver phyto nanoparticles were collected from plant extract and tested growth potential and metabolic pattern in (Lupinus termis L.) seedlings upon exposure to different concentrations of AgNPs. The seedlings were exposed to various concentrations of (0, 0.1, 0.3 and 0.5 mg L^?1) AgNPs for ten days. Significant reduction in shoot and root elongation, shoot and root fresh weights, total chlorophyll and total protein contents were observed under the higher concentrations of AgNPs. Exposure to 0.5 mg L^?1 of AgNPs decreased sugar contents and caused significant foliar proline accumulation which considered as an indicator of the stressful effect of AgNPs on seedlings. AgNPs exposure resulted in a dose dependent decrease in different growth parameters and also caused metabolic disorders as evidenced by decreased carbohydrates and protein contents. Further studies needed to find out the efficacy, longevity and toxicity of AgNPs toward photosynthetic system and antioxidant parameters to improve the current investigation.     

Substrate Temperature Effect on Microstructure,Optical, and Glucose Sensing Characteristics of Pulsed Laser Deposited Silver Nanoparticles

This work reports the substrate temperature-influenced change in the structural, morphological, optical, and glucose sensing properties of silver (Ag) nanoparticles (NPs) deposited on p-type Si (100) wafers. AgNP films grown at temperatures ranging from RT to 600 °C clearly show a dependence of orientation texture and surface morphology on substrate temperature (T _s). As T _s increases from RT towards 600 °C, the preferred orientation of AgNP film changes from (111) to (200). The AgNPs size, that is T _s-dependent, reaches the maximum value at T _s = 300 °C. This result is attributed to restructuring of AgNPs texture. Moreover, the AgNP shape also changes from ellipsoid to sphere as T _s increases from RT to 600 °C. Surface plasmon enhancement in photoluminescence intensity is observed with increase in T _s. It is found also that the AgNP film deposited at 300 °C has considerable reflectance reduction relative to the silicon substrate, in wavelength range of 300–800 nm and a progressive red shift of localized surface plasmon resonances caused by the adding of increasing quantities of glucose has been observed. As a proof of concept, we also demonstrate the capability of grown AgNP substrates for glucose detection based on surface enhanced Raman spectroscopy in physiological concentration range with short integration time 10 s, varying with T _s.     

Toxicity of biosynthetic silver nanoparticles on the growth,cell ultrastructure and physiological activities of barley plant

Silver nanoparticles (AgNPs) were biosynthesized using the cell-free filtrate of bacterium Proteus mirabilis, reacted with 1 mM of AgNO₃ solutions at 37 °C. The synthesis of AgNPs was monitored by UV–Vis spectroscopy and transmission electron microscopy (TEM) equipped with selected area electron diffraction (SAED). The results point to formation of spherical to cubical particles of AgNPs ranging in size from 5 to 35 nm with an average of 25 nm in diameter. The toxicity of Ag on barley (Hordeum vulgare L. cv. Gustoe) that was subjected to Ag⁺ as AgNO₃ and AgNPs was explored. The grain germination and seedling growth of barley decreased in the presence of 0.1 mM Ag⁺ and was inhibited at 1 mM Ag⁺. In contrast, our results indicated that the AgNPs at low concentration (0.1 mM) could be useful for barley grain germination and seedling growth. However, the higher concentrations of AgNPs (0.5 and 1 mM) reduced grain germination and exhibited a stronger reduction in the root length. A decline in the photosynthetic pigments and disorganization of chloroplast grana thylakoids in Ag⁺ and AgNPs-treated plants confirmed the leaf chlorosis. An increase of plastoglobuli within chloroplasts was observed in Ag⁺ and AgNPs-treated leaves. Ag⁺ caused dense aggregation of nuclear chromatin materials and degeneration of mitochondria. Ag⁺ and AgNPs increased contents of malondialdehyde, soluble proteins, total phenolic compounds and activity of guaiacol peroxidase in barley leaves; these results point to activation of plant defence mechanisms against oxidative stress in barley.     

Antimicrobial and hormetic effects of silver nanoparticles on in vitro regeneration of vanilla (<Emphasis Type="Italic">Vanilla planifolia</Emphasis> Jacks. ex Andrews) using a temporary immersion system

Microbial contamination is a serious problem in temporary immersion systems (TIS) during commercial micropropagation. The use of adequate doses of silver nanoparticles (AgNPs), formulated as Argovit?, is an alternative to reduce the contamination indices and promote development in plants. The aim of this study was to evaluate the antimicrobial and hormetic effects of Argovit on in vitro regeneration of vanilla (Vanilla planifolia) using a TIS. In vitro regenerated shoots were grown in Murashige and Skoog (MS) liquid medium with Argovit at five different concentrations (0, 25, 50, 100 and 200 mg/l) using a temporary immersion bioreactor system (RITA^®). At 30 days of culture, contamination percentage was evaluated and shoot regeneration and length were used to determine the hormetic response. Analysis of macro and micronutrient contents was performed. In addition, the effect of Argovit on total phenolic content (TPC), reactive oxygen species (ROS) production, antioxidant capacity (ORAC) and lipid peroxidation (LP-MDA) was determined. Results showed that bacterial contamination was reduced at 50, 100 and 200 mg/l of Argovit. Growth stimulation was observed at 25 and 50 mg/l of Argovit, while significant inhibition was detected at 100 and 200 mg/l of Argovit. Mineral nutrient analysis revealed changes in macro and micronutrient concentrations exerted by Argovit. Moreover, the presence of Argovit induced the production of ROS and increased total phenolic content, antioxidant capacity and lipid peroxidation with a dose-dependent effect. Results suggested that the production of ROS and mineral nutrition are key mechanisms of AgNPs-induced hormesis for vanilla. Therefore, the addition of 50 mg/l of Argovit in the culture media had an antimicrobial and hormetic effect. Use of Argovit could be an efficient strategy for commercial micropropagation of vanilla and other species.     

Mercury sensing and toxicity studies of novel latex fabricated silver nanoparticles

Safe and eco-friendly alternatives to currently used hazardous chemico-physical methods of silver nanoparticles (AgNPs) synthesis are need of time. Rapid, low cost, selective detection of toxic metals in environmental sample is important to take safety action. Toxicity assessment of engineered AgNPs is essential to avoid its side effects on human and non-target organisms. In the present study, biologically active latex from Euphorbia heterophylla (Poinsettia) was utilized for synthesis of AgNPs. AgNPs was of spherical shape and narrow size range (20–50 nm). Occurrence of elemental silver and crystalline nature of AgNPs was analyzed. Role of latex metabolites in reduction and stabilization of AgNPs was analyzed by FT-IR, protein coagulation test and phytochemical analysis. Latex-synthesized AgNPs showed potential in selective and sensitive detection of toxic mercury ions (Hg²⁺) with limit of detection around 100 ppb. Addition of Hg²⁺ showed marked deviation in color and surface plasmon resonance spectra of AgNPs. Toxicity studies on aquatic non-target species Daphnia magna showed that latex-synthesized AgNPs (20.66 ± 1.52 % immobilization) were comparatively very less toxic than chemically synthesized AgNPs (51.66 ± 1.52 % immobilization). Similarly, comparative toxicity study on human red blood cells showed lower hemolysis (4.46 ± 0.01 %) by latex-synthesized AgNPs as compared to chemically synthesized AgNPs causing 6.14 ± 0.01 % hemolysis.     

Optimizing of Gold Nanoparticles on Porous Silicon Morphologies for a Sensitive Carbon Monoxide Gas Sensor Device

A set of carbon monoxide (CO) gas sensors based on porous silicon (PSi)/gold nanoparticle (AuNP) hetro structures were fabricated. Different forms of PSi surface morphologies were studied as a substrate for growth of AuNPs. Simple dipping process of PSi in hydrogen tetrachloroaurate (III) solution (HAuCl₄) at fixed concentrations of 10⁻² M/3.5 HF was used to synthesize AuNPs. The n-type PSi was equipped through photo-electrochemical etching process at current density value of 10 mA/cm² under illumination condition of 530-nm wavelength and laser illumination intensity of 20 to 80 mW/cm². Three different forms of PSi morphology, meso, macro, and double layers with pore shapes and sizes, were prepared. The structural and surface morphology properties of PSi-based substrate before and after deposition of AuNPs were investigated through studying of scanning electron microscopy (SEM), photoluminescence (PL), and X-ray diffraction (XRD). The electrical property (J-V) was carried out in primary vacuum and CO at low pressure. The results show that PSi surface morphologies strongly influenced the AuNP sizes and hence the sensor performance. It was found that decrease the AuNP sizes could be occasioned in high and fast current response.

     

Establishment and characterization of Stevia rebaudiana (Bertoni) cell suspension culture: an in vitro approach for production of stevioside

A protocol has been standardized for establishment and characterization of cell suspension cultures of Stevia rebaudiana in shake flasks, as a strategy to obtain an in vitro stevioside producing cell line. The effect of growth regulators, inoculum density and various concentrations of macro salts have been analyzed, to optimize the biomass growth. Dynamics of stevioside production has been investigated with culture growth in liquid suspensions. The callus used for this purpose was obtained from leaves of 15-day-old in vitro propagated plantlets, on MS medium fortified with benzyl aminopurine (8.9 μM) and naphthalene acetic acid (10.7 μM). The optimal conditions for biomass growth in suspension cultures were found to be 10 g l^?1 of inoculum density on fresh weight basis in full strength MS liquid basal medium of initial pH 5.8, augmented with 2,4-dichlorophenoxy acetic acid (0.27 μM), benzyl aminopurine (0.27 μM) and ascorbic acid (0.06 μM), 1.0× NH₄NO₃ (24.7 mM), 3.0× KNO₃ (56.4 mM), 3.0× MgSO₄ (4.5 mM) and 3.0× KH₂PO₄ (3.75 mM), in 150 ml Erlenmeyer flask with 50 ml media and incubated in dark at 110 rpm. The growth kinetics of the cell suspension culture has shown a maximum specific cell growth rate of 3.26 day^?1, doubling time of 26.35 h and cell viability of 75 %, respectively. Stevioside content in cell suspension was high during exponential growth phase and decreased subsequently at the stationary phase. The results of present study are useful to scale-up process and augment the S. rebaudiana biological research.     

Phyto-synthesis of silver nanoparticles using <Emphasis Type="Italic">Alternanthera tenella</Emphasis> leaf extract: an effective inhibitor for the migration of human breast adenocarcinoma (MCF-7) cells

In this study, phyto-synthesis of silver nanoparticles (AgNPs) was achieved using an aqueous leaf extract of Alternanthera tenella. The phytochemical screening results revealed that flavonoids are responsible for the AgNPs formation. The AgNPs were characterised using UV–visible spectrophotometer, field emission scanning microscopy/energy dispersive X-ray, transmission electron microscopy, fourier transform infrared spectroscopy (FT-IR), and X-ray diffraction. The average size of the nanoparticles was found to be ≈48 nm. The EDX results show that strong signals were observed for the silver atoms. The strong band appearing at 1601–1595 cm^?1 correspond to C–C stretching vibration from dienes in FT-IR spectrum indicating the formation of AgNPs. Human breast adenocarcinoma (MCF-7) cells treated with various concentrations of AgNPs showed a dose-dependent increase in cell inhibition. The IC₅₀ value of the AgNPs was calculated to be 42.5 μg mL^?1. The AgNPs showed a significant reduction in the migration of MCF-7 cells.     

Biosynthesis and characterization of silver nanoparticles produced by Pleurotus ostreatus and their anticandidal and anticancer activities

The biosynthesis of nanoparticles has received increasing interest because of the growing need to develop safe, cost-effective and environmentally friendly technologies for the synthesis of nano-materials. In this study, silver nanoparticles (AgNPs) were synthesized using a reduction of aqueous Ag⁺ ions with culture supernatant from Pleurotus ostreatus. The bioreduction of AgNPs was monitored by ultra violet-visible spectroscopy and the obtained AgNPs were characterized by transmission electron microscopy (TEM) and Fourier transform infrared spectroscopy techniques. TEM studies showed the size of the AgNPs to be in the range of 4–15 nm. The formation of AgNPs might be an enzyme-mediated extracellular reaction process. Furthermore, the antifungal effect of AgNPs against Candida albicans as compared with commercially antifungal drugs was examined. The effect of AgNPs on dimorphic transition of C. albicans was tested. The anticancer properties of AgNPs against cells (MCF-7) were also evaluated. AgNPs caused a significant decrease in cell viability of an MCF-7 cell line (breast carcinoma). Exposure of MCF-7 cells with AgNPs resulted in a dose-dependent increase in cell growth inhibition varying from 5 to 78 % at concentrations in the range of 10–640 μg ml^?1. The present study demonstrated that AgNPs have potent antifungal, antidimorphic, and anticancer activities. The current research opens a new avenue for the green synthesis of nano-materials.     

Optimizing modes of inoculation of <Emphasis Type="Italic">Rhipicephalus</Emphasis> ticks (Acari: Ixodidae) with a mitosporic entomopathogenic fungus in the laboratory

The process of strain selection is an important step in the development of insect pathogens for biological control. Bioassays were conducted in the laboratory to evaluate the efficacy of different methods of inoculation using Rhipicephalus pulchellus Gerstäcker (Acari: Ixodidae) as a model. Initially, an oil-based formulation of Metarhizium anisopliae (Metsch.) Sorok. (Ascomycota: Hypocreales) titred at 10⁹ conidia ml^?1 was applied to R. pulchellus adults using a Burgerjon spray tower or a microapplicator. Inoculation by microapplicator yielded poor results (25.0% tick mortality) compared to Burgerjon’s spray tower (52.3% tick mortality), although the mean number of fungal conidia on R. pulchellus adults was lower (1.5 × 10⁴ ± 1.1 × 10³ conidia ml^?1) after spraying by Burgerjon’s spray tower compared to 1 × 10⁶ conidia ml^?1 obtained with the microapplicator. Thus, inoculation by Burgerjon’s spray tower was selected for further investigations. Different modes of inoculation were tested and included direct spray of inoculum on the tick and substrate (SS), direct spray on the substrate and tick followed by transfer of the tick to clean uncontaminated Petri dish (SP) or indirect inoculation of ticks through substrate (SW). The LC₅₀ values following contamination of nymphs (LC₅₀ = 1.4 × 10⁷ conidia ml^?1) and adults (LC₅₀ = 6.7 × 10⁷ conidia ml^?1) in SS were significantly lower compared to SP; nymphs (LC₅₀ = 5.7 × 10⁸ conidia ml^?1) and adults (LC₅₀ = 5.3 × 10⁹ conidia ml^?1) and SW; nymphs (LC₅₀ = 5 × 10⁸ conidia ml^?1). Although the LC₅₀ value in SS was the lowest, it recorded the highest tick mortality among control ticks (24.2% at 2 weeks post-treatment) and (23.3% at 3 weeks post-treatment) in nymphs and adults respectively compared to SP (2.5 and 5.8%, respectively) and SW (0.0 and 0.0). Results show that among the modes of inoculation tested, SP was the most appropriate for inoculating R. pulchellus adults. SW and SP were identified as appropriate techniques for infecting the R. pulchellus nymphs with conidia formulated in oil.     

On culture artefacts in coccolith morphology

Coccolith malformations occur more frequently in cultured specimens than in specimens from natural samples, a phenomenon commonly termed ‘culture artefacts’. The causes of culture artefacts are unknown. Here, we tested the effect of culture flask shape, mixing, and cell density on the morphology of Emiliania huxleyi coccoliths. While there was no effect of different culture flask types typically used in coccolithophore culturing, continuous mixing reduced the percentage of malformations by ca. 11 % in exponential-phase cells (cell density ca. 80 × 10³ cells per ml) and ca. 17 % in stationary-phase cells (cell density ca. 2 × 10⁶ cells per ml). Stationary-phase cells displayed 19 % more malformations than mid-exponential-phase cells when not mixed at all and 20 % more malformations when continuously mixed. It is concluded that the lack of mixing and unnaturally high cell densities, typical for coccolithophore stock cultures, are partly responsible for culture artefacts.     

Synthesis,characterization and evaluation of antimicrobial and cytotoxic activities of biogenic silver nanoparticles synthesized from <Emphasis Type="Italic">Streptomyces xinghaiensis</Emphasis> OF1 strain

We report synthesis of silver nanoparticles (AgNPs) from Streptomyces xinghaiensis OF1 strain, which were characterised by UV–Vis and Fourier transform infrared spectroscopy, Zeta sizer, Nano tracking analyser, and Transmission electron microscopy. The antimicrobial activity of AgNPs alone, and in combination with antibiotics was evaluated against bacteria, namely Escherichia coli, Pseudomonas aeruginosa, Staphylococcus aureus and Bacillus subtilis, and yeasts viz., Candida albicans and Malassezia furfur by using micro-dilution method. The minimum inhibitory concentration (MIC) and minimum biocidal concentration of AgNPs against bacterial and yeast strains were determined. Synergistic effect of AgNPs in combination with antibacterial and antifungal antibiotics was determined by FIC index. In addition, MTT assay was performed to study cytotoxicity of AgNPs alone and in combination with antibiotics against mouse fibroblasts and HeLa cell line. Biogenic AgNPs were stable, spherical, small, polydispersed and capped with organic compounds. The variable antimicrobial activity of AgNPs was observed against tested bacteria and yeasts. The lowest MIC (16 µg ml^?1) of AgNPs was found against P. aeruginosa, followed by C. albicans and M. furfur (both 32 µg ml^?1), B. subtilis and E. coli (both 64 µg ml^?1), and then S. aureus and Klebsiella pneumoniae (256 µg ml^?1). The high synergistic effect of antibiotics in combination with AgNPs against tested strains was found. The in vitro cytotoxicity of AgNPs against mouse fibroblasts and cancer HeLa cell lines revealed a dose dependent potential. The IC₅₀ value of AgNPs was found in concentrations of 4 and 3.8 µg ml^?1, respectively. Combination of AgNPs and antibiotics significantly decreased concentrations of both antimicrobials used and retained their high antibacterial and antifungal activity. The synthesis of AgNPs using S. xinghaiensis OF1 strain is an eco-friendly, cheap and nontoxic method. The antimicrobial activity of AgNPs could result from their small size. Remarkable synergistic effect of antibiotics and AgNPs offer their valuable potential in nanomedicine for clinical application as a combined therapy in the future.     

Process optimization of xylanase production using cheap solid substrate by Trichoderma reesei SAF3 and study on the alteration of behavioral properties of enzyme obtained from SSF and SmF

This study aimed to assess the variability in respect of titer and properties of xylanase from Trichoderma reesei SAF3 under both solid-state and submerged fermentation. SSF was initially optimized with different agro-residues and among them wheat bran was found to be the best substrate that favored maximum xylanase production of 219 U (gws)^?1 at 96 h of incubation. The mycelial stage of the fungi and intracellular accumulation of Ca⁺⁺ and Mg⁺⁺ induced maximum enzyme synthesis. Inoculum level of 10 × 10⁶ spores 5 g^?1 of dry solid substrate and water activity of 0.6 were found to be optimum for xylanase production under SSF. Further optimization was made using a Box-Behnken design under response surface methodology. The optimal cultivation conditions predicted from canonical analysis of this model were incubation time (A) = 96–99 h, inoculum concentration (B) = 10 × 10⁶ spores 5 g^?1 of dry substrate, solid substrate concentration (C) = 10–12 g flask^?1, initial moisture level (D) = 10 mL flask^?1 (equivalent to a _w  = 0.55) and the level of xylanase was 299.7 U (gws)^?1. Subsequent verification of these levels agreed (97 % similar) with model predictions. Maximum amount of xylanase was recovered with water (6:1, v/w) and under shaking condition (125 rpm). Purified xylanase from SSF showed better stability in salt and pH, was catalytically and thermodynamically more efficient over enzyme from SmF, though molecular weight of both enzymes was identical (53.8 kDa).     

Silver nanopaticles synthesized using the seed extract of Trigonella foenum-graecum L. and their antimicrobial mechanism and anticancer properties

Background

Synthesis of silver nanoparticles (AgNPs) through biological route plays an important role in their applications in the medical field, especially in the prevention of disease causing microbial pathogens and arresting the propagation of cancer cells. The stable, green synthesis of AgNPs is very much welcomed in the medical field because of their low toxicity. Therefore, the demands of AgNPs synthesised biologically is on the rise. The present study aimed to investigate the antimicrobial mechanisms and anticancer properties of the AgNPs synthesized using the seed extract of Trigonella foenum-graecum L. The AgNPs were characterized by UV–vis, SEM, XRD, FTIR and EDAX analysis. The minimum inhibitory concentrations (MIC) of the AgNPs were determined by the broth micro dilution method.

Effects of the Electrostatic Repulsion Between Nanoparticles on Colorimetric Sensing: An Investigation of Determination of Hg2+ with Silver Nanoparticles

The electrostatic repulsion between metal nanoparticles has an important effect on the colorimetric assays based on the aggregation of nanoparticles. In this work, an Hg²⁺ colorimetric sensor based on silver nanoparticles (AgNPs) was used as a model system to study the effects of electrostatic repulsion. Adenine nucleotides carrying different numbers of phosphate groups, adenosine monophosphate (AMP), adenosine diphosphate, and adenosine triphosphate, were used to functionalize AgNPs, respectively. Three kinds of AgNPs displayed different responses to Hg²⁺ ions due to the difference in electrostatic repulsion force, which is resulted from the varying of the number of phosphate groups. The density of negative charges on the surface of AgNPs exhibited a great affect on the size of the AgNPs, detection sensitivity and response range for Hg²⁺ ions. On these bases, the AMP-modified AgNPs were developed into highly sensitive colorimetric sensor to determine Hg²⁺ ions in aqueous solution, which showed a high sensitivity of 0.5 nM and excellent selectivity for Hg²⁺. The Hg²⁺ levels in water samples were determined using AMP-AgNPs with satisfied recovery. The studies on the role of electrostatic repulsion in the colorimetric assays will facilitate the development of more sensitive colorimetric sensors.     

Optimization of a MRC-5 Cell Culture Process for the Production of a Smallpox Vaccine

A cell culture process adaptable to produce smallpox vaccine at large scale has been developed. To achieve this, Design of Experiments (DOE) was applied to identify and optimize critical cell culture process parameters for MRC-5 cell growth and recovery during cell expansion. For cell growth, a 2^5?1 partial factorial (two level, five factor, 16 conditions) study was designed to evaluate the effects of basal media, seeding density, culture volume, feeding frequency and serum concentration on population doubling level (PDL) after 6–7 days in adherent T-flask cultures. Results indicated that lowering the cell density to 1×10⁴ cells/cm², increasing the culture volume to 0.5 ml/cm² and increasing serum concentration to 20% significantly improved cell expansion. These findings correlated with PDLs above 2.0 and cell densities above 1×10⁵ cells/cm² at the end of the study period. For cell recovery at passaging, a similar DOE was used to evaluate the effect of trypsin concentration, solution temperature, duration of treatment, incubation temperature and duration of standing time between quenching and reseeding. By increasing the trypsin treatment duration to 60 min and lowering the standing time between quenching and reseeding to within 1 h, the recovery of the MRC-5 cells was greatly improved. By using these newly defined conditions, a two-fold improvement in cell expansion was consistently achieved in both roller bottles and 10 layer Nunc^® Cell Factories (Cell Factories). Application of these new conditions for current Good Manufacturing Practices (cGMP) production of MRC-5 cell banks and clinical material demonstrated predictably high cell expansion as well as significantly higher production of vaccinia virus, thus providing the basis for manufacturing vaccinia virus at large scale. These findings demonstrate the need for cell culture optimization and the effectiveness of DOE to rapidly define processes suitable for cGMP manufacturing of a smallpox vaccine or other viral vaccine products.