Critical Reviews in Environmental Science and Technology, 44:1679–1739, 2014 Copyright © Taylor & Francis Group, LLC ISSN: 1064-3389 print / 1547-6537 online DOI: 10.1080/10643389.2013.790747
Biocatalytic Synthesis Pathways, Transformation, and Toxicity of Nanoparticles in the Environment AMARENDRA D. DWIVEDI1 and LENA Q. MA1,2
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1
State Key Laboratory of Pollution Control and Resource Reuse, School of the Environment, Nanjing University, Jiangsu, China 2 Department of Soil and Water Science, University of Florida, Gainesville, FL, USA
Wide application of nanoparticles (NPs) in consumer products over the last decade has increased their flux in the environment. This paper provides comprehensive review on the biocatalytic production pathways, transformations, and toxicity to human and other organisms of important NPs. Plants, algae, fungi, and bacteria have been used for energy-efficient and nontoxic biocatalytic production of NPs. The process is simple, serving as an alternative to the more popular physicochemical methods. NPs go through significant physicochemical transformation in the environment. Ionic strength, pH, and NPs’ surface potential strongly influence their stability and aggregation. Their transformations are linked to their bioavailability and aging including surface coatings and dissolved organic carbon effects. In addition, nanotoxicity has been a major global concern as NPs are toxic to organisms due to their cytotoxicity and genotoxicity. The stability and transformation of NPs in environment influence their short- and long-term toxicity. Release of free metal ions, dissolution-enhanced toxicity, and direct intercalation with biological targets are studied the most. Their toxicity to ecological receptors and organisms are linked to oxidative stress by generation of reactive oxygen species. Moreover, NPs toxicity depends on their physicochemical alterations. Inherent and acquired properties have potential to alter toxicity of NPs. Thus achieving safe nanotechnology and minimizing their adverse impact is important to protect the health of humans as well as the environment. Address correspondence to Lena Q. Ma, State Key Laboratory of Pollution Control and Resource Reuse, School of the Environment, Nanjing University, Jiangsu 210023, China. E-mail:
[email protected] 1679
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KEY WORDS: aggregation, bioavailability, biomimetics, nanoparticle, ROS, transformation
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I. INTRODUCTION Nanosciences started in the 1980s. The significant developments of cluster science and the invention of scanning tunneling microscope led to the discovery of fullerenes in 1986 and carbon nanotubes (CNTs) a few years later. In 2009 alone, >80,000 nano-related journal articles were published (Videa et al., 2011). Manufactured nanoparticles (NPs) from sunscreens to sensors affect every walk of human life (Table 1). NPs are currently widely used in optoelectronic devices, biochemical sensors, water purification, and catalysts. Also, nanomaterials (NMs) are expected to play an increasing role in areas such as chemotherapy, drug delivery, and labeling of food pathogen in coming years (Richardson, 2008). Biosynthesis of NPs based on natural materials is an emerging area of nanoscience. Natural environment provides crude unprocessed extract from tissues of different flora and fauna such as plants, marine organisms, and microbes, which contain structurally diverse chemical moieties and functional groups. This green method of synthesis overcomes the cumbersome processes of physicochemical methods. It is simple and eco-friendly when using natural extracts without adding extra surfactant, capping agent, and/or template to produce NPs. Nanotechnology bridges the crucial dimensional gap by linking the atomic and molecular scale of many fundamental sciences. However, no technology is ideally philanthropic in nature, so it also has its undesirable side. Figure 1 presents Amara’s law on the growth of nanotechnologies, nanoproducts, and nanowastes (Bystrzejewska et al., 2009). Environmental exposure due to anthropogenic release of NPs during their production and utilization cannot be ignored. Nanozerovalent iron (nZVI), for example, is injected into groundwater polluted with chlorinated solvents for remediation where NPs are released directly into water and soil. In addition, CNTs have been found in a coal–petroleum mix extracted from an oil well (Velasco-Santos et al., 2003). Fullerenes have been found in high concentrations (3 mg/kg to 1 g/kg) in Chinese ink sticks made from soot obtained by slow burning of oils (Heymann et al., 2003). Natural occurrences of NPs are also a major concern due to their potential toxicity. Chemical weathering processes of silicates, oxides, and other minerals frequently produce NPs including amorphous silica, hydrous aluminosilicates such as allophane, clays such as halloysite, and oxides such as magnetite and hematite. They are being detected in different matrices during volcanic activities and biochemical transformation. A probable exposure route for NPs toxicity is shown in Figure 2.
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Batteries
Air quality
Water quality
Sporting goods
Nanomaterial Applications
Nanotechnology enhanced membranes for water desalination Nano-composite catalyst for use in automotive catalytic converters Catalyst composed of manganese oxide NPs to remove volatile organic compounds (VOCs) Enzyme for removal of CO2 from industrial smoke stacks Lithium-ion battery with the cathode made from nano-phosphate Electrodes composed of NPs on a substrate for use in batteries Battery with chemicals isolated from electrode by “nanograss”
Nanocomposite barrier film Bicycle components with CNTs Golf shafts with NPs filling Golf balls using nano-enhanced polymer nsTM Tennis racquet frames with CNTs nCodeTM racquet frames with SiO2 NPs Deionization using electrodes made from nanosized carbon fibers Filter made from nanofibers is capable of removing viruses from water Fe NPs to treat groundwater pollutants
Application potential
(Continued on next page)
Faster charge and discharge rate than conventional electrodes Very long shelf life
Higher power, quicker recharge, and less combustion
Improved safety measures
Capable of destroying VOCs down to ppb level
Reduce cost due to lower platinum usage
Prevents air loss from tennis balls Strong, lightweight components Uniform golf shaft enabling a more consistent swing Improved energy transfer from golf club to ball Stiffer racquet provides more power Increases strength, stability, and power Lower energy and operating cost than conventional methods Lower cost than conventional filters of equivalent performance Less expensive than pumping water out of the ground for treatment Reduced cost for water desalination
Advantages
TABLE 1. Application potential of nanomaterial products by different industries across the world (www.understandingnano.com)
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Electronics
Solar cells
Chemical sensors
Cleaning products
Nanomaterial Applications
Higher power, and less combustion than standard lithium-ion batteries Higher power density, and low combustibility Kills bacteria and reduces odors Replace solvents with lower level of VOC’s and other pollutants Repels water and dirt to increase visibility with longer lifetime
Higher power, quicker recharge, and less combustion
Advantages
Liquid in which polymer molecules will align to bond with the glass and form a very thin, strong polymer film SNPs used in household appliances such as washer or Kills bacteria and reduces odors refrigerator Spray on liquid containing NPs which form a Repels water and dirt hydrophobic film CNT based sensors for detecting low levels of Quick evaluation of the respiratory status of medical industrial gas patients MEMS based sensor for detecting a wide range of For detecting a wide range of gases gasses Pd NPs-based hydrogen sensor Solar cell using NPs imbedded in plastic film Solar cell made with copper–indium–diselenide semiconductor ink Organic solar cell Solar cell made with silicon nanocrystalline ink Integrated circuits with nano-sized features Magnetoresistive random access memory (MRAM) Memory chips that use nano-scale probe tips to read and write data Self-assembled nanostructures Organic light-emitting diode (OLED) displays Nanophotonics Nanoemmissive displays
Ag–Zn battery using NPs in the silver cathode Spray on film containing TNPs Liquid cleaner using NPs
Lithium-ion battery with the anode composed of lithium titanate spindel NPs Lithium-ion battery using nanocomposite electrodes
Application potential
TABLE 1. Application potential of nanomaterial products by different industries across the world (www.understandingnano.com) (Continued)
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FIGURE 1. Amara’s law of correlation for nanotechnology showing nanohazards in long run (adopted from Bystrzejewska et al., 2009).
FIGURE 2. Prevalent development of toxicity of NPs upon exposure in humans.
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There has been increasing interest in the transformation and toxicity of NPs in the environment. Most investigations on NPs transformation consider metallic core and organic shell separately and seldom emphasize the coreshell structure together, which is vital for their transformations and toxicity in the environment (Levard et al., 2012). Oberdorster (2004) has observed that fullerenes were capable of crossing the blood-brain barrier in fish, which can be consumed by humans and cause potential toxicity. Moreover, soluble metal ions released from NPs make them bioavailable and toxic to different biota (Navarro et al., 2008a). This paper highlights the biocatalytic production pathways, transformation, and toxicity of NPs in the environment. It is divided into four sections including biocatalytic synthesis, transformation, toxicity, along with current perspective and future issues.
II. BIOCATALYTIC SYNTHESIS OF NPS Production of NPs based on natural materials is the state-of-the-art for their synthesis. The plant materials such as seed, leaf, flower, whole biomass, and plant latex have been used in biocatalytic production of NPs. This integrates nanotechnology with natural materials of plant kingdom in addition to combine with other branch of biology, which improves the formulation of new materials with diverse applications. Two major pathways including “top-down” or “bottom-up” are popular in NPs synthesis. Growth of living organisms in nature follows bottom-up pathways to synthesize NPs with fewer defects whereas major defects of crystallographic imperfections and surface structure damage are more pronounced in top-down pathways. Furthermore, surface plasmon resonance (SPR) is an important characterization tool for NPs biosynthesis. Due to the abundant free electrons from metallic NPs, their characteristic wavelength pattern can be measured using UV–Vis spectral analysis. The combined electron vibrations of NPs in resonance with light wave produce a distinctive pattern of SPR absorption band in UV–Vis region, thereby confirming formation of NPs from their macromolecular levels (Noginov et al., 2006; Nath et al., 2008).
A. Bioreduction Theory Biopolymers from plants and cell extract possess reductive enzymes and reducing agents, which can be used to produce NPs at room temperature and circumneutral pH in short time. A biocatalytic pathway for NPs synthesis is mainly through the reduction of metal salts, which acts as precursors for NPs. The kinetic factors for NP growth are controlled by precursor concentration, reductant power, nature of solvent (polarity and nonpolarity), and
Biocatalytic Synthesis Pathways, Transformation, and Toxicity of NPs
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appropriate shielding of the growth surface of NPs with a stabilizing agent. For example, abundant natural ascorbic acid has the ability to reduce metal ions into metal NPs where it acts as reductant in following manner (Jana et al., 2001) (Equation 1):
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(1)
Reduction reaction for a few metallic ions and their corresponding electrochemical reactions are summarized in Table 2, which are frequently used in the synthesis of metal NPs (Pradeep and Anshup, 2009).
B. Higher Plants Various plant species have been used to synthesize NPs based on their mild reduction ability. For example, the leaf extract of persimmon (Diopyros kaki) has been used to synthesize platinum NPs (Song et al., 2010) and the leaf extract of cycad (Cycas beddomei) and melde (Chenopodium album) has been used to produce silver NPs (SNPs) and gold NPs (GNPs) (Dwivedi and Gopal, 2010; Jha and Prasad, 2010). Reduction of Ag ions in solution was accomplished with the help of amentiflavone and hinokiflavone as well as ascorbates/glutathiones/metallothioneins in the leaves. The reduction and stabilization was attributed to different functional groups in various metabolites of terpenoids and reduced sugars in plant leaves. In addition, plant leaves have high levels of oxalic acid and aldehydic groups (Maruta et al., 1995), acting as both reducing agent and stabilizing ligand in NPs synthesis. Based on transmission electron microscopy (TEM) imaging, quasispherical particles were produced using leaf extract (Dwivedi and Gopal, 2010). Fourier transform infrared (FTIR) spectroscopy analysis indicated the possible involvement of carbonyl moieties in reduction process with carboxylate TABLE 2. Electrochemical reactions of various metallic ions Reactions Au3+ oxidised + 3e− → Au0 reduced − 0 Ag + oxidised + e → Ag reduced P d2+ oxidised + 2e− → P d0 reduced P t 2+ oxidised + 2e− → P t 0 reduced F e2+ oxidised + 2e− → F e0 reduced
Electrode potential (E 0reduction, in volts ) +1.50 +0.80 +0.83 +1.20 –0.44
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ions acting as shielding agent to stabilize NPs. Also, X-rays diffraction (XRD) analysis suggests transformation of elemental Ag and Au from metal salt solutions instead of their nano-oxides. Oxidation–reduction ability in plants is primarily owing to its phenolic antioxidant compounds, i.e., their ability to act as reducing agents, hydrogen donors, and singlet oxygen quenchers as well as their metal chelation potential (Kumarasamy et al., 2004). To synthesize SNPs and GNPs, oxalic acids can convert silver nitrate and auric acid to corresponding Ag and Au nanocolloid particles in a single step (Goia and Matijevic, 1999). Moreover, sorbic acid can also convert Ag and Au salts to metal NPs (Dubey et al., 2010b). FTIR analysis of native and NPs samples indicated the involvement of carbonyl functional group during the synthesis, with carboxylate ion shielding the developed NPs due to their negative surface charge (Dubey et al., 2010a). Dubey et al. (2013) employed a simple protocol to synthesize SNPs (25–42 nm) and GNPs (21–47 nm) using various plant leaf extracts (lingonberry, tansy, dandelion, lady’s mantle, and stinging nettle). Among the materials, tansy leaf-derived GNPs with higher negative zeta potential (–41.7 mV) was most stable. Jha et al. (2009) prepared SNPs (2–5 nm) using extracts from mesophytic (Cyperus sp.), hydrophytic (Hydrilla sp.), and xerophytic (Bryophyllum sp.) plants. Mesophytes, which are capable of nanotransformation, might have resulted from tautomerization of quinones. The mesophytic genera contain three types of benzoquinones, namely cyperoquinone, dietchequinone, and remirin. There is no observed pH shift in the extract during synthesis; however, mild warming and incubation may activate the quinones leading to particle size reduction as well as coalescent cluster formation (Figure 3). Moreover, regeneration of ascorbate is critical to maintain the antioxidative system in plants. Dehydroascorbate reductase catalyzes dehydroascorbate reduction to ascorbate. Catechol and protocatecheuic acid have also been reported in Hydrilla. Under alkaline conditions, catechol gets transformed into protocatechaldehyde and then to protocatecheuic acid. In both cases, reactive hydrogen gets liberated and takes part in synthesis of SNPs (Figure 4). In a similar way, oxaloacetic acid is formed from reaction of CO2 with phosphoenol pyruvate (PEP) by enzyme PEP carboxylase in xerophytic succulents (Bryophyllum sp.). Total tolerable acidity in Bryophyllum leaves increased from 2.2 g during night to 4.0 g during day at room temperature. The pool of organic acid gets constantly generated due to ongoing redox reactions in plant leaves. These changes helped the transformation of SNPs. In addition, chemical constituent emodin may undergo keto–enol tautomerization, which assists the reduction of Ag ions in the extract solution. Due to its abundance and ability to provide sites for metal cation binding, gelatin has been used as a matrix to disperse an aqueous Fe acetate precursor for NPs synthesis (Schnepp et al., 2010). Dispersing precursor Fe
Biocatalytic Synthesis Pathways, Transformation, and Toxicity of NPs O
O
O
H
Ag+
O
H
O
Cyperaquinone (keto form)
O
OH
O
O
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OH
(enol form)
O OCH3
H3CO
OH
O
OCH3
H
O OH
O OH
H
O
Rimirin (keto form)
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H3CO
OH
O
enol form
O H3CO
H O
H OH
Dietchequinone (keto form)
OCH3 OH
Ag0
(enol form)
FIGURE 3. Mesophytes pathways of NPs synthesis (Jha et al., 2009).
cation in an aqueous gel helps to form a homogeneous mixture of metal precursor. Consequently, the initial nucleation of iron oxide was constrained to NPs. The polymer simultaneously decomposed around these NPs and produced a C- and N-rich template, which prevents sintering of the oxide phase. Upon further heating, this template reacts with iron oxide, forming iron carbide (Fe3 C) NPs.
C. Microorganisms Microorganisms are known for their capability of metal transformation. Extracellular biosynthesis is more dominant than the intracellular biosynthesis in microorganisms. From thermodynamic point of view, e– acceptors are depleted according to their Gibb’s free energy in the order: O2 > NO3 – > Mn(IV) > Fe(III) > SO4 2– > CO2 . Oxygen is often preferred e– acceptor, but after its
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A. D. Dwivedi and L. Q. Ma HO
HO
HO
O
O
Ag+
HO
H
O
H
H
H
OH
HO
O
O
Ascorbic acid
Dehydroascorbic acid
OH OH
OH OH
OH
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O
OH
H H H H
Catechol
O
Protocatechaldehyde
O
OH
Protocatecheuic acid
Ag0 FIGURE 4. Hydrophytes pathways of NPs synthesis (Jha et al., 2009).
depletion, alternative e– acceptors are consumed sequentially (Seagren and Becker, 2002). Cyanobacteria generally use nitrate as the major source of nitrogen in the environment (Flores et al., 2005). Kalimuthu et al. (2008) reported the synthesis of SNPs by bacteria Bacillus lichemiformis, which were isolated from municipal biosolids. Nitrate reductase reduces Ag+ to Ag0 (Figure 5) (Mokhtari et al., 2009). Lengke et al. (2007) reported cyanobacteria reduce nitrate to nitrite and ammonium ions. In this way, Ag+ ions could be reduced by an intracellular electron donor (Equations 2–4): (2) (3) (4) Hyperthermophilic neutrophilic archaebacteria Pyrobaculum islandicum were utilized in extracellular production of spherical metal NPs of U(VI),
Biocatalytic Synthesis Pathways, Transformation, and Toxicity of NPs
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FIGURE 5. Bacillus lichemiformis-assisted NPs production pathways (Mokhtari et al., 2009).
Tc(VII), Cr(VI), Co(III), and Mn(IV) (Kashefi and Lovley, 2000). Their reduction depends on the presence of cell suspensions and hydrogen as e– donor. Moreover, P. islandicum has the ability to conserve energy using Fe(III) as a terminal e– acceptor and has the capability to transfer e– during metal reduction. Bacteria Enterobacter sp. showed a novel property of mercury (Hg) bioaccumulation via synchronized synthesis of intracellular Hg NPs (Sinha and Khare, 2011). Uniformly dispersed spherical Hg NPs were seen on the cell wall as well as inside the cytoplasm. Mechanism of Hg NPs synthesis is not fully understood but it could be mediated through reductase, followed by aggregation with other cellular proteins.
D. Fungi and Algae The shift from bacteria to fungi and algae to develop natural “nanofactories” has the added advantage in that downstream processing and handling of the biomass is much simpler. Several fungi species including Verticillium sp., Cladosporium cladosporioides, Trichoderma asperellum, and Volvariella volvacea and some species of Aspergillus, Penicillium, and Fusarium have been successfully used to synthesize metallic NPs (Table 3). The extracellular synthesis of bimetallic Au–Ag NPs by fungus Fusarium oxysporum biomass was reported by Ahmad et al. (2003a). The reduction of Ag+ was attributed to a nitrate-dependent reductase and a shuttle quinine extracellular process. The IR spectroscopic investigations have confirmed that amino acids and peptides form a coating, covering the SNPs to prevent them from agglomeration during extracellular synthesis using Fusarium semitectum (Basavaraja et al., 2008). Moreover, the filamentous fungus Neurospora crassa was used to produce monometallic and bimetallic SNPs and GNPs (Castro-Longoria et al., 2011). It showed potential for intracellular and extracellular synthesis of fairly monodispersed NPs. Dry powder of marine alga Sargassum wightii have been used to reduce aqueous AuCl4 – to
1690 10–35 21 39 5–30 — 5–50 3.2–6 1–4
Au Au Au Ag Au Ag, Au In2 O3 Pd Ti–Ni alloys Ag, Au Ag Ag Fe-oxide
Ocimum sanctum (leaf extract)
Ocimum sanctum (root extract) Moringa oleifera (leaf extract) Medicago sativa (Alfalfa)
10, 5 57 2–10
10–20, 30
10–20 15–50 15–20
16, 11 5–30 6–20 72.5 2–5 2–5 6.75–57.9
Ag Ag Pd
Ag, Au Ag Au ZnO Ag Ag Au
Plant part Tanacetum vulgare (tansy fruit) Mentha Piperita (leaf extract) Sesbania drummondii (seeds) Physalis alkekengi Hydrilla sp. Bryophyllum sp. Coriander leaf
Particle size (nm)
Jatropha curcas (latex) Jatropha curcas (seed extract) Cinnamon zeylanicum (cinnamon) Terminalia catappa (almond) (leaf) Lemon grass (leaf extract) Henna (leaf) Henna (leaf) Scutellaria barbata D. Don (barbated skullcup) Aloe vera Aloe vera (Aloe barbadensis Miller) Cinnamomum camphora Medicago sativa (Alfalfa)
NPs
Sources
TABLE 3. Various biocatalytic fabrication pathways of nanoparticles
Spherical and crystalline, hexagonal, triangular Spherical Spherical Crystalline
— FCC and complex arrays
Spherical/triangular Spherical
Spherical/triangular Anisotropic Quasispherical Spherical/triangular
Spherical
Spherical, triangle Spherical Spherical Crystalline Face centered cubic (FCC) FCC Spherical/triangle/truncated triangle/decahedral FCC Spherical Crystalline
Particle’s shape/Geometry
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Ahmad et al. (2010) Prasad and Elumalai (2011) Herrera-Becerra et al. (2008)
Yang et al. (2010) Schabes-Retchkiman et al. (2006) Philip and Unni (2011)
Chandran et al. (2006) Maensiri et al. (2008)
Pasricha et al. (2009) Kasthuri et al. (2009) Kasthuri et al. (2009) Wang et al. (2009a)
Ankamwar (2010)
Dubey et al. (2010a) Parashar et al. (2009b) Sharma et al. (2007) Qu et al. (2011a) Jha et al. (2009) Jha et al. (2009) Narayanan and Sakthivel (2008) Bar et al. (2009) Bar et al. (2009) Sathishkumar et al. (2009a)
References
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Psidium guajava (guava) (leaf extract) Pear fruit extract Parthenium (leaf extract) Tamarind (leaf extract) Neem (Azadirachta indica) leaf Geranium (Pelargonium graveolens) (leaf extract) Eucalyptus hybrida leaf Medicago sativa (Alfalfa) (biomass) Cinnamomum zeylanicum (leaf) Tea leaves extract Desmodium triflorum Acalypha indica leaf extract Euphorbia hirta (leaf) Cinnamon zeylanicum (cinnamon) Diospyros kaki (persimmon) (leaf extract) Hibiscus Rosa sinensis (leaf extract) Pelargonium graveolens (geranium) Syzygium aromaticum (clove buds) Honey Sorbus aucuparia (rowan) (leaf extract) Chenopodium album (leaf extract) Musa paradisiaca (banana peel extract) Eucalyptus citriodora (neelagiri) Avena sativa (oat) (biomass) Cubic Spherical/prism
Crystalline, irregular Spherical Rod-shaped
50–150 25 20 5–20 20–30 40–50 31–40 50–500 14 20–40 5–100 4 16–18 10–30 — ∼20 1 5–20 and 225–85
Ag Au Au Ag, Au Ag Ag Ag Ag Bimetallic Au/Ag Ag, Au Au Au Ag Ag, Au Ag, Au Ag Ag Au
Crystalline, irregular, spherical, elliptical Spherical Spherical, triangular, hexagonal Quasispherical
Decahedral, icosahedral
Spherical/prism Spherical/prism Spherical Spherical Spherical Cubic, hexagonal
Cubical Icosahedral/irregular
Triangular, hexagonal Irregular Triangle Spherical Quasilinear superstructures
200–500 ∼50 20–40 50–100 16–40
Au Ag Au Ag–Au Ag
Spherical
25–30
Au
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Ravindra et al. (2010) Armendariz et al. (2004) (Continued on next page)
Bankar et al. (2010)
Dwivedi and Gopal (2010)
Philip (2010b) Dubey et al. (2010b)
Deshpande et al. (2010)
Shankar et al. (2003a)
Philip (2010a)
Song and Kim (2008)
Dubey et al. (2009) Gardea-Torresdey et al. (1999) Smitha et al. (2009) Begum et al. (2009) Ahmad et al. (2011) Krishnaraj et al. (2010) Elumalai et al. (2010) Sathishkumar et al. (2009b)
Ghodake et al. (2010) Parashar et al. (2009a) Ankamwar et al. (2005) Shankar et al. (2004) Shankar et al. (2003b)
Raghunandan et al. (2009)
1692 16–40 100–400 29–92 2–6 25–80
Ag Ag Ag Ag Ag
Datura metel (leaf extract) Ipomoea aquatica Syzygium cumini (leaf and seed extract) Cycas sp. (cycas) leaf Nelumbo nucifera (lotus) (leaf extract)
20–50 and >100(cluster) n.d. 160–180
Ag Ag Au Ag Au, Ag, Au–Ag alloy CdS Ag
Bacillus licheniformis Shewanella algae Pseudomonas stutzeri
Clostridium thermoaceticum
Staphylococcus aureus
Lactobacillus
FCC crystalline
7.6 ± 1.8 and 4 7.3 ± 2.3 4 6.1 ± 1.6 50 10–20 200
Au
Bacillus subtilis
3
Spherical
4–5
Ag
Irregular
n.d.
n.d. n.d. Equilateral triangles/hexagons Hexagonal/other shape
Crystalline
2–12
Pt
Persimmon (Diopyros kaki) leaf extract MICROORGANISMS Bacteria Bacillus cereus
2–35
Ag
Spherical Spherical, triangular, truncated triangular, decahedral Spherical
Hexagonal wurtzite and spherical Spherical, ellipsoidal Spherical and cubic Spherical
Particle’s shape/Geometry
Brassica juncea (mustard)
53.7
ZnO
Sedum alfredii Hance
Particle size (nm)
NPs
Sources
TABLE 3. Various biocatalytic fabrication pathways of nanoparticles (Continued)
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Cunningham and Lundie (1993) Nanda and Saravanan (2009)
Nair and Pradeep (2002)
Kalishwaralal et al. (2008) Konishi et al. (2006) Tanja et al. (1999)
Ganesh Babu and Gunasekaran (2009) Reddy et al. (2010)
Haverkamp and Marshall (2009) Song et al. (2010)
Jha and Prasad (2010) Santhoshkumar et al. (2011)
Kesharwani et al. (2009) Roy and Barik (2010) Kumar et al. (2010)
Qu et al. (2011b)
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Klebsiella pneumonia, Escherichia coli, Enterobacter cloacae Pseudomonas aeruginosa Proteus mirabilis Rhodopseudomans capsulata Escherichia coli Geobacter sulfurreducens Brevibacterium casei Plectonema boryanum Bacillus subtilis, Lactobacillus acidophilus, Klebsiella pheumoniae, Escherichia coli, Enterobacter cloacae, Staphylococcus aureus, Candida albicans Morganella sp. Thermoanaerobacter ethanolicus Thermoanaerobacter ethanolicus Escherichia coli Thermomonospora sp. Fungi Alternaria alternata Volvariella volvacea, Mushroom Volvariella volvacea, Mushroom Verticillium Fusarium oxysporum Fusarium oxysporum Fusarium oxysporum Fusarium oxysporum Trichoderma viride Colletotrichum sp./geranium leaves Fusarium semitectum Spherical
Triangular/spherical/hexagonal Spherical Spherical and triangular n.d. Quasispherical Spherical/triangular Spherical/rod-like Variable (spherical/rod/flat sheet) Spherical
20 ± 5 41.3 30–100 2–5 8 20–60 ∼15 20–150 25 ± 12 20–40 5–20 3–11 5–15 5–40 20–40 10–60
Ag Fe3 O4 Fe3 O4 CdS Au Ag Ag Au Ag Au CdS, zirconia Ag Ag Au Ag
Spherical Spherical
Octahedral Spherical/elliptical Spherical
n.d. Spherical Spherical Spherical n.d. Spherical Spherical n.d.
15–30 10–20 10–20 50 30 10–50 200 50–100
Au Ag Au Ag Ag Ag Ag Ag
Spherical
∼52.5 (average)
Ag
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Basavaraja et al. (2008) (Continued on next page)
Mukherjee et al. (2001) Mukherjee et al. (2002) Ahmad et al. (2002) Bansal et al. (2004) Ahmad et al. (2003a) Fayaz et al. (2010) Shankar et al. (2003a)
Philip (2009)
Gajbhiye et al. (2009) Philip (2009)
Parikh et al. (2008) Yeary et al. (2005) Zhang et al. (1998) Sweeney et al. (2004) Ahmad et al. (2003b)
Husseiny et al. (2007) Samadi et al. (2009) He et al. (2007) Gurunathan et al. (2009) Law et al. (2008) Kalishwaralal et al. (2010) Lengke et al. (2007) Minaeian et al. (2008)
Shahverdi et al. (2007)
1694 2–5 2 1–1.5 90%) appeared in the nonaerated tank in fullerenes. Thus, geometric arrangement of CNTs leads to variable toxicity. Surface coatings have profound effects on toxicity of CNTs. Tabet et al. (2011) investigated surface coating effect of CNTs on BALB/c mice intratracheally and murine macrophages. The polystyrene-coated CNTs showed a weak toxicity without affecting their intrinsic structure. In contrast, acidbased CNTs induced higher toxicity including oxidative stress and inflammation in the lungs of mice during 6 months monitoring. The hydrophilic carboxylic group on the CNTs surfaces facilitates the internalization of CNTs. In addition, cell adherence to hydrophobic materials reduces internalization of polystyrene-based CNTs and their toxicity (Arima and Iwata, 2007). Furthermore, functional groups affected phototoxicity of C60 by altering photochemistry (Snow et al., 2012). Functionalization with bis- and trisfulleropyrrolidinium ions exhibited more efficient 1O2 sensitization rates than aminofullerenes (Lee et al., 2009). In addition, 1O2 exposure to MS2 bacteriophage virus showed its disinfection ability by rapid viral inactivation. Nanodiamonds (NDs) are also toxic to organisms (Schrand et al., 2007; Perez et al., 2009; Mohan et al., 2010; Zhang et al., 2010). Different functional groups on NDs are responsible for their cytotoxicity and in vivo toxicity based on human embryonic kidney 293 cells (HEK 293 cells) and Xenopus embryos (Marcon et al., 2010). The safe concentration limit was < 50 μg/mL by HEK 293 cell viability assays. Concentration above this level causes cytotoxic responses due to their affinity for the negatively charged cell membrane. Overall, cytotoxicity of NDs decreased in the order: NDsNH2 (>50 μg/mL) > NDs-OH (>100 μg/mL) > NDs-CO2 H (∼200 μg/mL).
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In addition, early-stage embryos of Xenopus showed higher embryotoxicity and teratogenicity to NDs-CO2 H at >20 μg/mL, showing phenotypical abnormalities and high mortality during their gastrulation and neurulation developmental stages. Moreover, NDs-OH showed the least impact on embryo survival at 2–200 μg/mL whereas NDs-NH2 was slightly toxic. Among environmental studies on fullerenes, C60 has been investigated the most, although other types of fullerenes exist (Hull et al., 2009). Some studies focused on the impact of C60 NPs on entire communities and ecosystems (Navarro et al., 2008b). But, in spite of existing studies, the in vivo fate and the chronic toxicity of fullerenes is still debated, possibly due to uncertainty associated with the contribution of amorphous and metal impurities in C60 NPs (Aschberger et al., 2010; Henry et al., 2011; Szwarc and Moussa, 2011).
C. Titanium Dioxide Titanium dioxide, known for its electrical insulating properties, becomes conductive or change from insoluble to more soluble at
