erp.legacyrealties.com/the-man-in-lonely-land.php Directed self-assembly is one of the emergent technologies which find interest to the researchers currently [ 1 — 10 ]. Directed self-assembly approach is still going through developmental phases and leverages existing patterning methods by combining those with self-organizing systems to create manufacturing techniques that can be readily integrated into existing processes. Spontaneous self-assembly is introduced as an evaporation-induced phenomenon that yields random patterns.
Among guided self-assembly approaches employing some guiding agent to nanoparticles or vapour of atoms , template-guided and field-guided assemblies are two approaches. Among field guided assembly, use of pressure gradient, magnetic field, electric field, electron beam, light and laser, etc. The present article reviews the progress so far in the direction of establishment of directed self-assembly as a reproducible and robust technique and its future prospects for its usage at industrial scale.
The use of spontaneous self-assembly as a lithography- and external field-free which means to construct well-ordered often intriguing structures has received much attention for its ease of organizing materials on the nanoscale into ordered structures and producing complex, large-scale structures with small feature sizes. An extremely simple route to intriguing structures is the evaporation-induced self-assembly EISA [ 11 — 18 ] of polymers and nanoparticles from a droplet on a solid substrate. However, flow instabilities within the evaporating droplet often result in non-equilibrium and irregular dissipative structures, e.
Therefore, fully utilizing evaporation as a simple tool for creating well-ordered structures with numerous technological applications requires precise control over several factors, including evaporative flux, solution concentration, and the interfacial interaction between solute and substrate [ 23 — 31 ] Fig.
As shown in Fig. The metal particle size and size distribution depends on the deposition conditions, e. After transport the substrates and conditions on the substrate surface play an important role in determining the microstructural evolution of the films. It is pertinent at this point to recall the process of condensation of vapor into thin films on substrates [ 32 ].
Initially small nuclei, depending on the effective surface energy available, form on the substrate. Once a few nuclei form, they work as nucleation centers. Coalescence between nuclei occurs, and this finally gives rise to the growth of continuous layers.
Nanoparticulate formation in particular can be attributed to the metal—substrate interactions. Energetics decides the contact angle of the condensate onto the substrate, residual strain, and size and shape of the nanoparticles deposited. The capillary model predicts that free energy of formation of condensed aggregate goes through a maximum [ 32 ]. With heating of the substrate, densification occurs, and the grain wall boundary width is thinned.
At RT deposition conditions, because sufficient energy is not available for mobility of adatoms on the substrate surface, the size is not enhanced much due to coalescence. Occasionally, some short distance orderlinesses as shown in Fig. The organization of inorganic nanostructures within self-assembled organic or biological templates [ 33 — 43 ] is receiving the attention of scientists interested in developing functional hybrid materials. Previous efforts have concentrated on using such scaffolds [ 39 , 44 ] to spatially arrange nanoscopic elements as a strategy for tailoring the electrical, magnetic, or photonic properties [ 40 — 43 , 45 — 48 ] of the material.
Recent theoretical arguments [ 48 — 50 ] have suggested that synergistic interactions between self-organizing particles and a self-assembling matrix material can lead to hierarchically ordered structures. Lin et al. MWNT has been aligned [ 31 ] as shown in Fig. The z scale is 50 nm for all images [ 52 ]. The assembly of nanoparticles into ordered architectures is a potential route to achieve further construction and miniaturization of electronic and optical devices.
Among guided self-assemblies, a template-guided self-assemblies and b field-guided self-assemblies are two broad divisions. Among template-guided self-assemblies, use of physical templates, chemical templates and biological templates are three ways to achieve orientation in the growth features. Physical template has to do with physical existence of ridge, depth, patterning on the substrate surface. Unsatisfied bonds can in principle work as chemical templates. Use of DNA as a biological template for guided self-assembly has been attracting attention to biochemists and biophysicists.
Advantages with physical template-assisted fabrication of nanowires lie in the fact that they combine fabrication with organization and solve integration issues eliminating the need to manipulate individual nanowires. Issues related to contacts for electrical and magnetotransport are also solved. Moreover, physical vapour deposition techniques such as evaporation, sputtering and Pulsed Laser Deposition PLD are well-known industrially applicable techniques, and hence fabrication of nanowires using these approaches is also expected to be very useful.
Use of physical templates gives rise to the growth of nanomaterials at pre-defined position eliminating the need of post-growth manipulation and providing the ease of electrical connections for further characterizations. Porous anodic alumina [ 53 — 56 ] and silica [ 57 ] membrane have been widely used to grow patterned nanodot arrays in a routine manner by scientific community. Recently, Ru nanostructure fabrication has been reported [ 58 ], using an anodic aluminium oxide nanotemplate and highly conformal Ru atomic layer deposition as shown in Fig.
Such templates give rise to the growth of nanodots, vertical nanowires, which can be controllably used to fabricate FET devices, magnetic tunnel junction devices and devices for optical applications. Fabrication of nanomaterials using porous alumina templates has been reviewed [ 59 ]. However, use of in-plane growth of nanowires and array of nanodots seems to be more promising.
Ravi Shankar et al. They reported that the growth in most of the cases occurs at the top ridge of the groove which they attributed to electric field singularity positions. Brown et al. The nanoclustered nanowires usually grow at the apex of the trench as shown in Fig. If the V-groove trench be shallow, then more vapour would get access inside the trench, and therefore, one can expect nanowire growth on the trench sidewalls inside. Current author has exploited this aspect of thin film growth inside the V-groove trench template to achieve nanowire growth on the apex and sidewalls of the trenches.
They have demonstrated that very long nanowires can be fabricated with good control of diameter [ 62 — 64 ]. Nanowire diameter is the deposition thickness-dependent. Thin film material—substrate combination is also crucial for providing perfect dewetting conditions as shown in Fig. This figure demonstrates the growth features of nickel by thermal evaporation SEM image in Fig. In all the cases, first array of nanodots grows, and then at larger deposition thickness of the material, nanowire growth takes place. Gold-tipped CdSe rods nanodumbbells were solubilized in an aqueous phase and self-assembled in a head-to-tail manner using biotin disulphide and avidin [ 65 ].
The disulphide end of the biotin molecule attaches to the gold tip of the nanodumbbell, and the biotin end of the molecule is able to conjugate to an avidin protein. The avidin can strongly conjugate up to four biotin molecules. Changing the ratios of biotin to nanodumbbells leads to the formation of dimers, trimers, and flowerlike structures.
To further improve the distribution of chain lengths, a separation method based upon weight was applied using a concentration gradient. The gold tips provide effective anchor points for constructing complex nanorod structures by self-assembly. Metal-directed self-assembly of two- and three-dimensional synthetic receptors has been reviewed recently [ 66 ]. Biomolecule-directed strategies have shown great promise in assembling nanoparticles into a wide diversity of architectures, because of their high efficiency, high specificity and genetic programmability [ 67 ]. Such nanoassembled materials have been shown to have potential applications in new detection systems, such as biosensors [ 68 ] and chemical sensors [ 69 , 70 ], and in the construction of nanoelectronic devices [ 71 ].
DNA-directed self-assembly of gold nanoparticles into binary and ternary Nanostructures has recently been demonstrated [ 72 ] as shown in Fig. Two sizes of gold nanoparticles 10 and 30 nm average diameters were used for the purpose. These regulations from the US and EU, as well as other countries such as Japan and Canada, reveal that nanotoxicity via cosmetics are of major concern for both scientific policymakers and industries producing consumer products [ — ].
Since , the FDA has been working on identifying sources of NMs, estimating the environmental impact of NMs and their risks on people, animals and plants, and how these risks could be avoided or mitigated [ ]. This article demands for a strong and comprehensive oversight of products generated from NMs. This encompasses a precautionary foundation for specific nanomaterial regulations, health, and safety of the public and workers, transparency, public participation, environmental protection, as well as the inclusion of broader impacts and manufacturer liability [ ].
Similarly, the Nanomaterials Policy Recommendations report covers ways to avoid or reduce the risk of NMs in food-related industries. This report also advises companies to adopt a detailed public policy for NMs usage, publish safety analyses of NMs, issue supplier standards, label NPs below nm and adopt a hazard control approach to prevent exposure to NPs [ ].
Researchers and manufacturers should be educated on the regulatory laws and legislations prior to nanomaterial production to avoid these types of bans against NMs. It is currently agreed that NMs are not intrinsically hazardous per se and many of them seem to be nontoxic, while others have beneficial health effects. However, the risk assessment in the future will determine whether the NMs and their products are hazardous or any further actions are needed.
The toxicity profiling of NMs is a highly demanded research area worldwide in recent times. Natural NMs have been present in the ecosystem for years, and they possess some mechanisms to cause less harmful effects among living organisms. However, research advancements have found some acute toxic effects of nanosized particles in living systems.
From this review article, it can be noted that NMs from anthropogenic activities and engineered NMs in consumer products are able to cause toxic effects in living creatures. Additionally, emerging NPs, such as viral NPs and nanozymes, should be subjected to rigorous cytotoxicity tests to establish benign mechanisms of application and dosage levels. In order to minimize or avoid the potential hazards of engineered NMs in consumer products, regulations and laws have been implemented in many countries.
Extensive research in the field of nanotoxicology and strict laws by government agencies are essential to identify and avoid toxic NPs. National Center for Biotechnology Information , U. Journal List Beilstein J Nanotechnol v. Beilstein J Nanotechnol. Published online Apr 3. Author information Article notes Copyright and License information Disclaimer. Corresponding author. Ahmed Barhoum: ge. Received Sep 29; Accepted Mar 9. This article has been cited by other articles in PMC.
Abstract Nanomaterials NMs have gained prominence in technological advancements due to their tunable physical, chemical and biological properties with enhanced performance over their bulk counterparts. Keywords: nanomaterial classification, nanomaterial history, nanotoxicity, oxidative stress, reactive oxygen species, regulations. Review Introduction Nanoparticles NPs and nanostructured materials NSMs represent an active area of research and a techno-economic sector with full expansion in many application domains.
Recently, the British Standards Institution [ 7 ] proposed the following definitions for the scientific terms that have been used: Nanoscale: Approximately 1 to nm size range. Nano-object: Material that possesses one or more peripheral nanoscale dimensions. Nanostructured materials: Materials containing internal or surface nanostructure. Types and classification of nanomaterials Most current NPs and NSMs can be organized into four material-based categories the references refer to recent reviews on these different categories of NMs.
Open in a separate window. Figure 1. Classification of nanomaterials based on their dimensions The production of conventional products at the nanoscale currently helps and will continue to will help the economic progress of numerous countries. Classification of nanomaterials based on their origin Apart from dimension and material-based classifications, NPs and NSMs can also be classified as natural or synthetic, based on their origin.
History and development of nanomaterials Humans already exploited the reinforcement of ceramic matrixes by including natural asbestos nanofibers more than 4, years ago [ 22 ]. Sources of nanomaterials Sources of nanomaterials can be classified into three main categories based on their origin: i incidental nanomaterials, which are produced incidentally as a byproduct of industrial processes such as nanoparticles produced from vehicle engine exhaust, welding fumes, combustion processes and even some natural process such as forest fires; ii engineered nanomaterials, which have been manufactured by humans to have certain required properties for desired applications and iii naturally produced nanomaterials, which can be found in the bodies of organisms, insects, plants, animals and human bodies.
Incidental nanomaterials Photochemical reactions, volcanic eruptions, and forest fires are some of the natural processes that lead to the production of natural NPs as mentioned. Figure 2. Figure 3. Engineered nanomaterials Simple combustion during cooking, in vehicles, fuel oil and coal for power generation [ 83 ], airplane engines, chemical manufacturing, welding, ore refining and smelting are some of the anthropogenic activities that lead to NP formation [ 84 ]. Naturally produced nanomaterials Apart from incidental and engineered nanomaterials, nanoparticles and nanostructures are present in living organisms ranging from microorganisms, such as bacteria, algae and viruses, to complex organisms, such as plants, insects, birds, animals and humans.
Figure 4. Figure 5. Nanoparticles and nanostructures in plants Wood is made of natural fibers that are considered as cellular hierarchical bio-composites. Figure 6. Nanoparticles and nanostructures in insects Insect wing membranes are comprised of building materials with 0. Nanoparticles and nanostructures in animals and birds Animals insects belonging to Kingdom Animalia such as flies, spiders, and geckos with varying body weight can attach along ceilings and move along vertical walls.
Figure 7. Nanoparticles and nanostructures in the human body The human body consists of nanostructures without which normal function of the body is impossible. Table 1 List of nanostructured particles associated with the human body. Nanostructure Size Ref. Bone nanostructures The inimitable combination of natural bone with precise and carefully engineered interfaces and mechanical properties is due to their nanoscale to macroscopic architectural design and dimensions. Figure 8. Other nanostructures in the human body Antibodies, enzymes, proteins and most organelles within cells are smaller than the micrometer-scale and are considered nanostructures.
Challenges and risk assessment of nanomaterials Recent articles and the frameworks reviewed in previous studies, outline the general properties of NMs regarding risk assessment. Table 2 Summary of five basic nanomaterial properties and their potential risks and challenges. Nanomaterial properties Risk description agglomeration or aggregation Weakly bound agglomeration and fused particles are significant risk criteria as they lead to poor corrosion resistance, high solubility and phase change of NMs. This further leads to deterioration and the structure maintenance becomes challenging [ — ].
Chemical species and their charge-related critical functional groups will be a significant factor for specific functionality and bioavailability of NMs [ ]. Due to this reason, encapsulation becomes a prime necessity for solution-based NP synthesis chemical route. In the encapsulation process, the reactive nano-entities are encapsulated by nonreactive species to provide stability to the NPs.
For example, sulfur impurities may present in iron oxide NPs depending on the precursor used for their production FeCl 3 or Fe 2 SO 4 3. Similarly, nickel, yttrium, or rubidium metal impurities may be present in the carbon nanotubes CNTs [ — ] that are adsorbed on the CNT surface. It is well known that the process of agglomeration will happen at slower rates in smaller particles. After the synthesis of the NPs, it is impossible to retain their original size. Hence, encapsulation becomes highly inevitable in NP synthesis.
The exceptional size-dependent chemistry of NPs is distinguished from classical colloid chemistry by categorizing NPs according to their particle size [ ]. The experimental results of NP exposure are not available and their potential toxicity issues are still under question.
Nanomaterial toxicity Humans are exposed to NPs as they are produced by natural processes [ 64 ]. Figure 9. Nanomaterial regulations Nanomaterials possess characteristics such as high chemical bioactivity and reactivity, cellular as well as tissue and organ penetration ability, and greater bioavailability.
Conclusion The toxicity profiling of NMs is a highly demanded research area worldwide in recent times. References 1. Regul Toxicol Pharmacol. Geneva, Switzerland: International Organization for Standardization; Interpretation and implications of the European Commission's definition on nanomaterials; Letter report Potocnik J. Off J Eur Communities: Legis.
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