Synthesis of gold nanoparticles by various leaf fractions of Semecarpus anacardium L. tree

Gold nanoparticles (NPs) were synthesized using Semecarpus anacardium leaf extracts in water and the green biomass. Extract prepared at ambient condition by crushing the leaves in deionized water is identified as ‘green extract’, and that by boiling the leaf pieces as ‘boiled extract’. The mass remaining after separating the ‘green extract’ is identified as ‘green biomass’. These components triggered rapid reduction of Au(III) to Au (0) in HAuCl₄ solution indicating the natural ability of the leaves of S. anacardium to synthesize NPs in ambient conditions. Green extract produced more NPs compared to the boiled extract suggesting denaturization of some of the useful factors due to boiling. NPs were quantified using UV and ICP-AES analysis. These were characterized using Transmission electron microscopy, Fourier transform infrared spectroscopy and X-ray diffraction. TEM images of the particles formed with green extract, boiled extract and green biomass showed that the particles were of different shapes and sizes.     

Biorecovery of gold using cyanobacteria and an eukaryotic alga with special reference to nanogold formation – a novel phenomenon

Pro- and eukaryotic algal genera, i.e. Lyngbya majuscula, Spirulina subsalsa (Cyanophyceae) and Rhizoclonium hieroglyphicum (Chlorophyceae), were used for bio-recovery of gold (Au) out of aqueous solution. Au (III) spiked with ¹⁹⁸Au was used for the experiment. Batch laboratory experiments indicated quick metabolic independent binding of Au to the algae followed by active accumulation and subsequent reduction. Gold accumulation by different algal genera was found in order of R. hieroglyphicum > L. majuscula > S. subsalsa (3.28, 1.93 and 1.73 mg g^-1, respectively). It was observed that the algal biomass and the media used for the experiment turned purple in colour indicating reduction of Au (III) to Au (0) at intra- and extracellular level. This was confirmed by TEM studies of L. majuscula biomass exposed in HAuCl₄ solution where <20-nm-sized gold particles were found both inside as well as on the surface of the cell. Up to 90–100% of accumulated gold was recovered from the algal biomass by using nitric acid and acidic thiourea solution.     

Fine structure of in situ microbial iron deposits

The fine structure of iron deposits produced by Leptothrix spp. from two caverns and a surface spring were observed. In the case of Leptothrix pseudovacuolata, the iron occurred as an amorphous deposit within the cell sheath and the cells contained gas vesicles. In the case of the other Leptothrix spp., the iron was deposited within the cell sheath either as a hexagonal or fibrillar matrix. In the case of fibrillar iron deposits, fibrils resembling those of the sheath were found within the cytoplasm of the cells. This suggests that the deposition of iron could have occurred within the cells as well as at the cell surface. In some cases, the fine structure of microbial iron deposits could provide a means of distinguishing biological from abiological iron deposition.     

Biosorption and Bioreduction of Trivalent Aurum by Photosynthetic Bacteria <Emphasis Type="Italic">Rhodobacter capsulatus</Emphasis>

Biosorption has been shown to be an eco-friendly approach to remove heavy metal ions. In this study, the photosynthetic bacteria Rhodobacter capsulatus was screened and found to have strong ability to adsorb Au(III). The maximum specific uptake of living cells was over 92.43 mg HAuCl₄/g dry weight of cell in the logarithmic phase. Biosorpion ability would be enhanced by an acidic environment. As the main cations, during biosorption the quantity of Mg²⁺ exchanged was more than Na⁺. Biosorbed Au(III) could be reduced by carotenoid and enzymes embedded and/or excreted by R. capsulatus, which might be the mechanism of photosynthtic bacteria metal tolerance.     

Carbohydrate-directed synthesis of silver and gold nanoparticles: effect of the structure of carbohydrates and reducing agents on the size and morphology of the composites

A monosaccharide (β-d-glucose) and polysaccharide (soluble starch) were used as structure directing and subsequently stabilizing agents for the synthesis of spherical nanoparticles (NPs) and nanowires of silver and gold. Homogeneous monodispersed Ag(0) nanoparticles (Ag NPs) of 15 nm diameter were obtained when 10⁻⁴ M AgNO₃ precursor salt was reduced in starch (1 wt %)–water gel by 1 wt % β-d-glucose. For a second preparation the effect of reducing agents on the synthesis of Au(0) metallic nanoparticles (Au NPs) of 2 × 10⁻⁴ M concentration prepared in a β-d-glucose (0.03 M)–water dispersion was studied first in detail. Different equivalent amounts of NaBH₄ and a number of pH values were evaluated for the reduction of the Au salt HAuCl₄·3H₂O to obtain Au NPs. The type and the amount of reducing agent, as well as the pH of the solution was shown to affect the size and morphology of the NPs. NaBH₄ (4 equiv) produced the smallest (5.3 nm (σ 0.7)) metallic particles compared to larger particles (10.0 nm (σ 1.4)) when the salt was reduced by 1 equiv of NaBH₄. Addition of excess NaBH₄ caused the NPs to settle out as a precipitate forming a mesh or wire structure rather than monodispersed particles. Low pH (pH 6) resulted in incomplete reduction, while at pH 8 the salt was completely reduced. When the salt was reduced by NaOH at pH 8, the particles were larger (14.2 nm) and less homogeneous (σ 2.8) compared to those from NaBH₄ reduction.     

Mycogenesis of gold nanoparticles using a phytopathogen <Emphasis Type="Italic">Alternaria alternata</Emphasis>

The development of an eco-friendly and reliable process for the synthesis of gold nanomaterials (AuNPs) using microorganisms is gaining importance in the field of nanotechnology. In the present study, AuNPs have been synthesized by bio-reduction of chloroauric acid (HAuCl₄) using the fungal culture filtrate (FCF) of Alternaria alternata. The synthesis of the AuNPs was monitored by UV–visible spectroscopy. The particles thereby obtained were characterized by UV, dynamic light scattering (DLS), X-ray diffraction (XRD), energy dispersive X-ray (EDX) analysis, Fourier transform infrared (FTIR) spectroscopy, atomic force microscopy (AFM) and transmission electron microscopy (TEM). Energy-dispersive X-ray study revealed the presence of gold in the nanoparticles. Fourier transform infrared spectroscopy confirmed the presence of a protein shell outside the nanoparticles which in turn also support their stabilization. Treatment of the fungal culture filtrate with aqueous Au⁺ ions produced AuNPs with an average particle size of 12 ± 5 nm. This proposed mechanistic principal might serve as a set of design rule for the synthesis of nanostructures with desired architecture and can be amenable for the large scale commercial production and technical applications.     

Formation of Au(III)-DNA Coordinate Complex by Laser Ablation of Au Nanoparticles in Solution

We discovered that an Au(III)-DNA coordinate complex, Au(III)(DNA-base)₂(amine)l, are formed by laser ablation of Au nanoparticles in an aqueous solution containing DNA molecules in the presence of amines and multi-valent cations, where l represents an unknown ligand (either amine or water). Optical absorption spectrum of the solution after laser ablation exhibited a 360 nm absorption peak assigned to ligand→Au(III) charge transfer (LMCT) band of the coordinate complex. The complex is considered to be formed as follows: 1) the DNA molecules are neutralized by binding the multi-valent cations to their negatively charged phosphate groups, and adsorbed on the surface of the Au nanoparticles by a hydrophobic interaction, 2) Au(III) ions are liberated from the Au nanoparticles by laser ablation, and 3) an Au(III) ion reacts with amine and two DNA bases of a DNA molecule into an Au(III)(DNA-base)₂(amine)l.     

Resonance light scattering determination of trace bisphenol A with signal amplification by aptamer–nanogold catalysis

HAuCl₄ was reduced by sodium citrate to prepare 10 nm gold nanoparticles (AuNPs) that were modified by the bisphenol A aptamer (Apt) to obtain an aptamer–nanogold probe (Apt‐AuNP) for bisphenol A (BPA). The probes were aggregated nonspecifically to form large clusters, which showed a strong resonance light scattering (RLS) peak at 520 nm, under preparation conditions (pH 7.6 Na₂HPO₄‐NaH₂PO₄ buffer and ultrasonication). Upon addition of BPA, the probe reacted specifically to form dispersed BPA‐Apt‐AuNP conjugates that exhibited strong catalysis of the two particle reactions of glucose‐Cu(II) and hydrazine hydrochloride‐Cu(II) with a strong RLS peak at 360 nm and 510 nm respectively. When the BPA concentration increased, the RLS intensity at 360 nm and 510 nm increased respectively. Accordingly, two new and highly‐sensitive RLS methods were established for the detection of BPA, using the Apt‐AuNP catalytic amplification. Copyright © 2013 John Wiley & Sons, Ltd.     

Purification, characterization and reassembly of the bacteriophage T4D tail sheath protein P18.

P18, the sole component of T4 tail sheath, has been isolated in a monomeric active form from extended sheaths of intact tails which were dissociated at low ionic strength. The molecular weight of P18 is determined to be 65,000 from sedimentation equilibrium and 73,000 from sodium dodecyl sulphate/gel electrophoresis. Combining the diffusion constant (D_20,w = 5·5× 10^?7cm²s^?1)and the sedimentation constant (s⁰_20,w = 4·2 S) a value of 67,000 is obtained. The circular dichroism spectra reveal a striking similarity of the structure of P18 in the monomeric state and in the extended sheath conformation.The purified P18 is found to reassemble into extended sheaths if the core-baseplate complex is present, forming normal length tails. Structures similar to polysheath are formed in the absence of core-baseplates.     

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.

     

Soil stabilization by a prokaryotic desert crust: Implications for Precambrian land biota

A cyanophyte dominated mat, desert crust, forms the ground cover in areas measuring hundreds of square meters in Utah and smaller patches in Colorado. The algal mat shows stromatolitic features such as sediment trapping and accretion, a convoluted surface, and polygonal cracking. Sand and clay particles are immobilized by a dense network of filaments of the two dominating cyanophyte species,Microcoleus vaginatus andM. chthonoplastes, which secrete sheaths to which particles adhere. These microorganisms can tolerate long periods of desiccation and are capable of instant reactivation and migration following wetting. Migration occurs in two events: 1. immediately following wetting of dry mat, trichomes are mechanically expelled from the sheath as it swells during rehydration, and 2. subsequently, trichomes begin a self-propelled gliding motility which is accompanied by further production of sheath. The maximum distance traveled on solid agar by trichomes ofMicrocoleus vaginatus during a 12 hour period of light was 4.8 cm. This corresponds to approximately 500 times the length of the fastest trichome, and provides a measure of the potential for spreading of the mat in nature via the motility of the trichomes.Dehydration resistence of the sheath modifies the extracellular environment of the trichomes and enables their transition to dormancy. Following prolonged wetting and evaporative drying of the mat in the laboratory, a smooth wafer-like crust is formed by the sheaths ofMicrocleus trichomes that have migrated to the surface. Calcium carbonate precipitates among the algal filaments under experimental conditions, indicating a potential for mat lithification and fossilization in the form of a caliche crust. It is suggested that limestones containing tubular microfossils may, in part, be of such an origin.The formation of mature Precambrian soils may be attributable to soil accretion, stabilization, and biogenic modification by blue-green algal land mats similar to desert crust.     

Effect of continuous application of manures and fertilizers on rhizosphere microflora in arecanut palm

Summary The rhizosphere microflora of arecanut palm under continuous application of organic manures and inorganic fertilizers was studied. The nutrients applied are 100 g N, 40 g P₂O₅ and 140 g K₂O/palm/year in the form of organics and inorganics. The application of organic manure increased the microbial population. The increase in microbial population was observed between the rhizosphere samples collected at 0–30cm and 30–60 cm depths. The surface cultivation of soil increased the microbial population.Trichoderma sp. andAspergillus sp. dominated in therhizosphere of arecanut palm. Contribution No. 208. Central Plantation Crops Research Institute, Vittal-574243, Karnataka, India.     

Chemiluminescence of off‐line and on‐line gold nanoparticle‐catalyzed luminol system in the presence of flavonoid

It was found that flavonoids could remarkably inhibit the chemiluminescence (CL) intensity of an off‐line gold nanoparticle (AuNP)‐catalyzed luminol–H₂O₂ CL system. By contrast, flavonoids enhanced the CL intensity of an on‐line AuNP‐catalyzed luminol–H₂O₂ CL system. In the off‐line system, the AuNPs were prepared beforehand, whereas in the on‐line system, AuNPs were produced by on‐line mixing of luminol prepared in a buffer solution of NaHCO₃ ? Na₂CO₃ and HAuCl₄ with no need for the preliminary preparation of AuNPs. The on‐line system had prominent advantages over the off‐line system, namely a lowering of the background noise and improvements in the stability of the CL system. The results show that differences in the signal suppression effect of flavonoids on the off‐line AuNP‐catalyzed CL system are influenced by the combined action of a free radical scavenging effect and occupy‐sites function; the latter was proved to be predominant using controlled experiments. Enhancement of the on‐line system was ascribed to the presence of flavonoids promoting the on‐line formation of AuNPs, which better catalyzed the luminol–H₂O₂ CL reaction, and the enhancement activity of the six flavonoids increased with the increase in reducibility. This work broadens the scope of practical applications of an AuNP‐catalyzed CL system.     

DIFFERING ONTOGENETIC ORIGINS OF PCR (“KRANZ”) SHEATHS IN LEAF BLADES OF C4 GRASSES (POACEAE)

The origin and early development of procambium and associated ground meristem of major and minor veins have been examined in the leaf blades of seven C₄ grass species, representing different taxonomic groups and the three recognized biochemical C₄ types (NAD-ME, PCK, and NADP-ME). Comparisons were made with the C₃ species, Festuca arundinacea. In “double sheath” (XyMS+) species (Panicum effusum, Eleusine coracana, and Sporoboìus elongatus), the procambium of major veins gives rise to xylem, phloem, and a mestome sheath; associated ground meristem differentiates into PCA (“C₄ mesophyll”) tissue and the PCR (“Kranz”) sheath. Development in the C₃ species parallels this pattern, except that associated ground meristem differentiates into mesophyll and a parenchymatous bundle sheath. In contrast, major vein procambium of “single sheath” (XyMS–) species (Panicum bulbosum, Digitaria brownii, and Cymbopogon procerus) differentiates into xylem, phloem and a PCR sheath; associated ground meristem gives rise to PCA tissue. These observations of major vein development support W. V. Brown's hypothesis that the PCR sheaths of “double sheath” (XyMS+) C₄ grasses are homologous with the parenchymatous bundle sheaths of C₃ grasses, while in “single sheath” (XyMS–) C₄ species they are homologous with the mestome sheath. Although there are some similarities in the development of the major and minor vascular bundle procambium in the C₄ species examined, the ontogeny of the smaller minor veins is characterized by a precocious delineation of the PCR sheath layer that may even precede the appearance of the distinctive cytological features of ground meristem and procambium. This contracted development in minor veins appears to be related to their close spacing in mature leaves and to their comparatively late appearance during leaf ontogeny.     

Penetration into rice tissues by brown planthopper and fine structure of the salivary sheaths

The fine structure of the salivary sheaths in plant tissues can provide important information on homopteran probing and ingestion behaviors. Salivary sheaths secreted by the brown planthopper (BPH), Nilaparvata lugens (Stål) (Homoptera: Delphacidae), and their tissue pathway were investigated using light, scanning electron, and transmission electron microscopy. About half of the salivary flanges on the surface of the food substrate were connected with internal salivary sheaths. Only 43% of the salivary sheaths showed side branches. Many sculpture‐like protuberances and small cavities had been formed on the outer surface of the salivary sheath, but the sheath lumen circumferences were sealed. Brown planthoppers showed a preference for probing and leaving salivary sheaths in the susceptible rice variety TN1 rather than in the resistant variety B5 during the first 2 days of the experiments. The salivary sheaths in rice tissues reached the inner tissue layer of the leaf sheaths and stems, but were mostly observed to end in the first and second layer of the leaf sheaths. Brown planthoppers also preferred to probe into the thick segment of the outer leaf sheath. After ingestion by the insect, the cytoplasm in both phloem and companion cells degraded and the main organelles were lost. Numerous small vesicles were found in most of the phloem cells, but cell walls remained intact. Large numbers of symbiont‐like structures were observed inside the salivary sheath lumen. These results indicated that BPH has complicated feeding behaviors, which warrants further investigation.     

Increased Abundance of Gallionella spp., Leptothrix spp. and Total Bacteria in Response to Enhanced Mn and Fe Concentrations in a Disturbed Southern Appalachian High Elevation Wetland

The Sorrento wetland hosts several Fe- and Mn-rich seeps that are reported to have appeared after the area was disturbed by recent attempts at development. Culture-independent and culture-based analyses were utilized to characterize the microbial community at the main site of the Fe and Mn seep. Several bacteria capable of oxidizing Mn(II) were isolated, including members related to the genera Bacillus, Lysinibacillus, Pseudomonas, and Leptothrix, but none of these were detected in clone libraries. Most probable number assays demonstrated that seep and wetland sites contained higher numbers of culturable Mn-oxidizing microorganisms than an upstream reference site. When compared with quantitative real time PCR (qPCR) assays of total bacteria, MPN analyses indicated that less than 0.01% of the total population (estimated around 10⁹ cells/g) was culturable. Light microscopy and fluorescence in situ hybridization (FISH) images revealed an abundance of morphotypes similar to Fe- and Mn-oxidizing Leptothrix spp. and Gallionella spp. in seep and wetland sites. FISH allowed identification of Leptothrix-type sheath-forming organisms in seep samples but not in reference samples. Gallionella spp. and Leptothrix spp. cells numbers were estimated using qPCR with a novel primer set that we designed. Results indicated that numbers of Gallionella, Leptothrix or total bacteria were all significantly higher at the seep site relative to the reference site (where Gallionella was below detection). Interestingly, numbers of Leptothrix in the seep site were estimated at only 10⁷ cells/g and were not statistically different in the late summer versus the late winter, despite dramatic changes in sheath abundance (as indicated by microscopy). qPCR also indicated that Gallionella spp. may represent up to 10% (3 × 10⁸ cells/g) of the total bacteria in seep samples. These data corroborate clone library data from samples taken in October 2008, where 11 SSU rRNA sequences related to Gallionella spp. were detected out of 77 total sequences (roughly 10–15%), and where Leptothrix sequences were not detected. Analysis of this SSU rRNA clonal library revealed that a diverse microbial community was present at seep sites. At a 3% difference cutoff, 30 different operational taxonomic units were detected out of 77 sequences analyzed. Dominant sequence types clustered among the beta- and gamma- Proteobacteria near sequences related to the genera Ideonella, Rhodoferax, Methylotenera, Methylobacter, and Gallionella. Overall, results suggest that high metal concentrations at the seep sites have enriched for Fe- and Mn-oxidizing bacteria including organisms related to Gallionella and Leptothrix species, and that members of these genera coexist within a diverse microbial community.     

A Simple Method for the Size Controlled Synthesis of Stable Oligomeric Clusters of Gold Nanoparticles under Ambient Conditions

Reducing dilute aqueous HAuCl₄ with sodium thiocyanate (NaSCN) under alkaline conditions produces 2 to 3 nm diameter nanoparticles. Stable grape-like oligomeric clusters of these yellow nanoparticles of narrow size distribution are synthesized under ambient conditions via two methods. The delay-time method controls the number of subunits in the oligoclusters by varying the time between the addition of HAuCl₄ to alkaline solution and the subsequent addition of reducing agent, NaSCN. The yellow oligoclusters produced range in size from ~3 to ~25 nm. This size range can be further extended by an add-on method utilizing hydroxylated gold chloride (Na⁺[Au(OH_4-x)Cl_x]^-) to auto-catalytically increase the number of subunits in the as-synthesized oligocluster nanoparticles, providing a total range of 3 nm to 70 nm. The crude oligocluster preparations display narrow size distributions and do not require further fractionation for most purposes. The oligoclusters formed can be concentrated >300 fold without aggregation and the crude reaction mixtures remain stable for weeks without further processing. Because these oligomeric clusters can be concentrated before derivatization they allow expensive derivatizing agents to be used economically. In addition, we present two models by which predictions of particle size can be made with great accuracy.     

Molecular regulation of sink–source transition in rice leaf sheaths during the heading period

The upper leaf sheath of rice (Oryza sativa L.) serves as a temporary starch sink before heading, subsequently becoming a carbon source tissue to the growing panicle at the post-heading stage. The time of sink–source transition in upper leaf sheaths is highly correlated to the panicle exsertion. Here, we found that the expression profiles of starch synthesis genes such as ADP-glucose pyrophosphorylase large subunit 2, granule-bound starch synthase II, soluble starch synthase I, starch branching enzyme (SBE) I, SBEIII, and SBEIV were highly correlated with starch content changes during the heading period in the second leaf sheath below the flag leaf. In addition, the α-amylase2A and β-amylase were considered as major genes that were in charge of starch degradation at the post-heading period. Of the five sucrose transporter (OsSUT) genes, OsSUT1 and OsSUT4 appeared to play an important role in sucrose loading into the phloem of source leaf sheaths. Moreover, the microarray-based data implied that the dominant processes associated with functional leaf sheath transition from sink to source were carbohydrate metabolism and the translocation of the carbon and nitrogen sources and inorganic phosphate.     

Silver Fused Conducting Fiber Formation of Au–Ag Core-Shell Nanoparticles Mediated by Ascorbic Acid

In this paper, we report the spontaneous formation of fibrous structures consisting of assemblies of Au–Ag core-shell nanoparticles (NPs) from a solution consisting of Au–Ag core-shell NPs and l-ascorbic acid (AA). AA acted both as the reducing agent for the generation of NPs and also as the mediator for the formation of fibers. The process of fiber formation involved three steps—reduction of HAuCl₄ to Au NPs by AA, subsequent formation of Au–Ag core-shell NPs after addition of AgNO₃, and spontaneous formation of fibers from the mixtures in water. It took typically about 30 days to form complete fibers that are of lengths of several hundred micrometers to millimeters, although nanofibers started forming from the first day of solution preparation. The width of each of these fibers was typically about 1–4 μm with length of each segment of fiber bundle, on the order of 40 μm. Formation of fibers was also observed in absence of AgNO₃. These fibers consisted of Au NPs and polymer of AA degradation products and were not electrically conducting. Also, low concentrations of AgNO₃ produced fibers with low electrical conductivity. However, it was observed that increase in the amount of AgNO₃ leads to the formation of fibers that were electrically conducting with conductivity values in the range of metallic conductivity. Spectroscopic and electron microscopic investigations were carried out to establish the formation of fibers. The details of fiber formation mechanism under different conditions and electrical conductivities of the fibers are discussed in the article.     

Environmentally benign rapid biosynthesis of extracellular gold nanoparticles using Aspergillus flavus and their cytotoxic and catalytic activities

In this study, the rapid biosynthesis of gold nanoparticles (AuNPs) by Aspergillus flavus culture supernatant was achieved by reducing 1 mM of chloroauric acid (HAuCl₄) within 2 min at pH 7 and 30 °C. The biosynthesized nanoparticles exhibited maximum absorbance at 545 nm in UVvis spectroscopy. Transmission electron microscopy exhibited that AuNPs tend to take nearly spherical shapes with an average size of 12 nm. Fourier transform infrared analysis indicated that carboxyl, amine, and hydroxyl groups may participate in the biosynthesis and stabilization of AuNPs. Its zeta potential was found to be -33.01 mV. Energy dispersive X-rays showed a strong and typical beak of gold nanocrystallites with 80.84 % of analyzed sample. X-Ray diffraction spectrum displayed Bragg reflections identical to the gold nanocrystals. The results confirmed that biosynthesized AuNPs are a potent anticancer agent against A549, HepG2 and MCF7 cell lines with IC₅₀ value 53.5, 60.7 and 100 μg/mL, respectively. Crystal violet assay confirmed the cytopathic effects of AuNPs on HepG2 and A549 cell lines. Annexin-V FITC assay and cell cycle confirmed the apoptotic effect and cell cycle arrest in G2/M phase, respectively for A549 cell line. Moreover, the results showed a degradation efficiency of AuNPs to 4-nitrophenol within 16 min.