The bottom up approach is a process that builds towards larger and more complex systems by starting at the molecular level and maintaining precise control of molecular structure. Top-down method: Top-Down method refers to a set of fabrication technologies which fabricate by removing certain parts from a bulk material substrate.
The removing methods can be mechanical, chemical, electrochemical and etc. There are a couple of manufacturing technologies in the conventional scale which can be categorized top-down. Milling is a representative example. In the milling process, material is selectively removed from the substrate, usually a metal sheet, forming a cavity with certain geometries.
The dimensions of the cavity depend on the travel path of the mill, which can be precisely controlled with the help of computer assisted numerical systems. The milling technique, along with similar methods such as drilling and grinding, is the most widely used technique in conventional manufacturing industry. People have attempted to extend top-down method into nanometer domain and supplemented the mechanical removing methods with chemical and electrochemical methods Fig.
Bottom-up method: As the opposite to top-down fabrication technologies, bottom-up methods refer to a set of technologies which fabricate by stacking materials on top of a base substrate.
These methods are similar in principle to welding and riveting at the conventional scale, in which a different type of material is attached to the base component by melted solder or physical fitting. In welding and riveting, attention is mainly paid to the strength of the contact area in order to maintain the construct as a reliable component for high load application.
Similarly, in bottom-up nanofabrication, the adhesion of the surface layer to the base substrate is also an important concern. There is extensive research on the surfactants to enhance adherence and avoid cracks during the subsequent processing. Research has also focused on autonomous patterning of the surface layer into nanometer scale features since, manipulation of nanoscale components is not ever an easy task as compared to that at the conventional scale Fig. At low laser flux, the material is heated by absorbed laser energy and evaporates or sublimates.
At higher flux, the material is converted to plasma. As a result of inter atomic collisions with gas atoms in chamber, the evaporated metal atoms lose their kinetic energy and condense in the form of small crystals which accumulate on liquid nitrogen filled cold finger.
So, in the search of for cheaper pathways for nanoparticle synthesis, scientists used microorganisms and then plant extracts for synthesis.
Nature has devised various processes for the synthesis of nano-and micro-length scaled inorganic materials which have contributed to the development of relatively new and largely unexplored area of research based on the biosynthesis of nanomaterials Mohanpuria et al.
The three main steps in the preparation of nanoparticles that should be evaluated from a green chemistry perspective are the choice of the solvent medium used for the synthesis, the choice of an environmentally benign reducing agent and the choice of a non toxic material for the stabilization of the nanoparticles. Most of the synthetic methods reported to date rely heavily on organic solvents. This is mainly due to the hydrophobicity of the capping agents used Raveendran et al.
Synthesis using bio-organisms is compatible with the green chemistry principles: the bio-organism is 1 eco-friendly as are 2 the reducing agent employed and 3 the capping agent in the reaction Li et al. Often chemical synthesis methods lead to the presence of some toxic chemical species adsorbed on the surface that may have adverse effects in medical applications Parashar et al. This is not an issue when it comes to biosynthesized nanoparticles as they are eco friendly and biocompatible for pharmaceutical applications.
Application areas of nanobiotechnology Bioanalysis: The life sciences research market continually seeks improvements in bioanalytical research tools with regard to further miniaturization, the ability to conduct experiments in parallel and improvements in sensitivity. There are limitations associated with the accuracy and resolution of fluorescent labelling methods and often the speed and cost of target amplification methods create a critical bottleneck in the design of ultrahigh-throughput bioanalytical systems.
Nanoscale bioanalytical technology platforms seek to eliminate some of these limitations. These platforms include the use of nanoparticles dots, bars, rods as labels for biomolecules for separation and screening, as well as nanopore and nanoscale fluidic assay systems and self-assembling arrays of nanoparticles. Such applications are more amenable to ultrahigh-throughput formats and theoretically provide more sensitive and highly-specific detection and analysis capabilities.
For example, current advances being made with nanoparticles promise to significantly improve signal generation and detection in high throughput, multiplexed biological assays. If successful, these developments will greatly enhance research productivity in the life sciences, significantly reduce the time, effort and expense of DNA sample preparation and analysis and find broad application in the clinical, food, agriculture and environmental markets.
Diagnostics: Nanotechnology is at the core of advances in the biosensor field through the use of novel materials, improved surface engineering and patterning techniques and systems integration. Biosensors are being developed using nanowires, nanoparticle arrays and nanofluidics systems-devices will likely include the integration of many of these components. These materials permit unprecedented sensitivity to our internal and external environment.
For example, with the ability to detect proteins down to a few molecules, the field of diagnostics can be brought to the fundamental level of a single cell.
And for patient monitoring and diagnosis, the assay may require only a single breath. The key to biosensing lies in the sensitivity of molecular detection, which is often determined by the method attachment of biomolecules to the sensor surface. General methods of coupling biomolecules to sensors include physical adsorption, covalent bonding, membrane entrapment and porous encapsulation.
Detection can be performed optically, electrochemically, thermally or through various other techniques. The biosensor market can be broken down to three basic categories: diagnostics for clinical and research use, nutritional and consumer product safety and chemical and biological warfare defense.
Therapeutics: Of the Life Sciences, this area has taken the quickest advantage of advances in nanotechnology. While some of the earliest applications have appeared in sunscreens and cosmetics, methods have been developed for in vivo drug delivery via nanoparticles such as nanocrystals, nanospheres, nanocapsules and can also include dendrimer technologies.
By the nature of their size, these nano delivery systems traverse membrane boundaries and can be readily absorbed into the bloodstream. Their surface chemistry can be modified to display high concentrations of a therapeutic drug or tissue-specific targeting molecules; alternatively the drug may be encapsulated for controlled stealth mode activity.
Surface coatings can also manipulated to exhibit fast or slow release, or for higher in situ stability and shelf-life. Drugs may be reformulated as nanocrystals or encapsulated for more efficient uptake.
Targeted nanotherapeutics suggest the promise tissue-specific delivery with a strong localized dose-requiring a lower overall concentration of the drug, while at the same time providing lower patient toxicity and side-effects. In some cases, payload delivery might be triggered by a secondary mechanism such as light activation. Nanotechnology may be able to accelerate therapeutics for protein and macromolecule drugs, infectious disease and cancer.
Nanoparticle inhalation technology provides a patient-friendly alternative to injection and may permit a lower dose strategy with protein drugs like insulin. With the ability to cross the blood-brain barrier, there may be new methods to diagnose and treat neurodegenerative disease.
And finally, there are promising new treatments using nanocapsules for cholesterol removal and nanostructured silicon to treat osteoporosis. Medical devices: Nanoscale devices open up a new horizon in medical diagnostics and treatment, as technological advances in materials and biosensors become precursors for advancing medical applications.
Current contrast agents require catheterization and have limited tissue specificity and retention rates, requiring immediate imaging. Here, nanoparticles may be useful at lower doses for tissue-specific targeting and retention. More significantly, nanoparticles have the advantage of slow diffusion out of the bloodstream, which could permit imaging of the circulatory system and blood pool-particularly useful in cases of stroke. In the area of cancer treatment, the removal of tumours is typically done through a combination of surgery, chemotherapy and radiation, to varying degrees of success but at some cost to the general health of the patient.
Similar to targeted drug delivery, nanoparticles may be useful as site-specific probes for tissue destruction, using light or heat to induce thermal oblation or deposit a localized chemotherapy payload.
For future applications, nanostructured silicon may prove useful as temporary scaffolding in reconstructive bone surgery and it has been demonstrated that nanoparticles can assist the generation of new bone matrix material. Prostheses can be designed with nanoporous interface to enhance integration of artificial structures and living tissue.
Not too much farther down the road, devices like retinal implants can take advantage of nanoscale solar technology, where nanoporous electrodes provide a high-density interface with the nerves of the retina. Nanoparticles as tools in medicine: It has proved difficult to channel pharmaceuticals into the brain. A type of cell barrier protects the brain from pathogens and many harmful molecules.
This blood-brain barrier also denies access to many therapeutic substances. Studies have shown that nanoparticles diameter between 10 and nm with distinct surface properties can overcome this barrier. At the University of Frankfurt am Main, a team headed by Prof. Magnetic nanoparticles could also be of use in combating cancer, as shown by the so called magnetic liquid hyperthermia developed by Dr.
Andreas Jordan and co-workers at the Charite Hospital in Berlin: Firstly, iron oxide particles are selectively transported into the carcinoma.
Then, an alternating magnetic field heats the nanoparticles and thus the cancer cells, which are killed by overheating. Helmut Schmidt and colleagues from INM attempt to modify the surface of the nanoparticles according to the requirements of the Berlin group so that the particles can be delivered to the blood stream. Above all, only cancer cells incorporate the particles, so that healthy cells are unaffected. Protein design for optical information processing: Bacteriorhodopsin originates from so called halobacteria using this protein to convert light energy into other suitable forms of energy.
Bacteriorhodopsin changes colour from purple to yellow when it is irradiated by light. The photochromic properties can selectively be modified and stabilised with the aid of genetic techniques. This entails it is interesting as a high-performance material for optical media, especially for holographic pattern recognition and interferometry. Many other applications are also possible. For example, biofilms coated with the protein can be produced thus creating optical data memory systems with extremely high capacities.
In the past few years, the necessary biotechnological tools have been established so that bacteriorhodopsin can be technologically exploited. Research is currently undertaken on integrating the new material into optical systems ready for application. In order to answer this question, an assessment of the specific risks is needed. For the application of nanotechnology in medical technology the risks which are judged to need special attention are related to the toxicology of nanoparticles and nanostructures.
Biological synthesis of nanoparticles from Indian perspective: There has been considerable significant research in India in the field of biological synthesis of nanoparticles. More research has been found to be concentrated in the area of synthesis using terrestrial plants and marine medicinal plant s.
Recently stable gold nanoparticles have been synthesized using the marine alga, Sargassum wightii. Nanoparticles with a size range between 8 to 12 nm were obtained using the seaweed. An important potential benefit of the method of synthesis was that the nanoparticles were quite stable in solution Singaravelu et al.
Extracellular biosynthesis of functionalized silver nanoparticles was done by using strains of Cladosporium cladosporioides fungus Balaji et al. Biosynthesis of zirconia nanoparticles has been done using the fungus Fusarium oxysporum Bansal et al. It has been observed that a novel alkalothermophilic actinomycete, Thermomonospora sp. The use of algae for the biosynthesis of nanoparticles is a largely unexplored area.
There is very little literature supporting its use in nanoparticle formation. Aspergillus flavus Vigneshwaran et al. Monodisperse silver nanoparticles with a size range of 8. Previously, Vigneshwaran et al. The average particle size was found to be 8. The intracellular synthesis of gold nanoparticles produced by V. Fungi are more advantageous compared to other microorganisms in many ways. Fungal mycelial mesh can withstand flow, pressure, agitation and other conditions in bioreactors or other chambers compared to plant materials and bacteria.
These are fastidious to grow, easy to handle and easy for fabrication. The extracellular secretions of reductive proteins are more and can be easily handled in downstream processing. Since the nanoparticles precipitated outside the cell is devoid of unnecessary cellular components, it can be directly used in various applications. Kowshik et al. These nanoparticles were used to fabricate diode heterojunction with poly p-phenylenevinylene. Similarly, Pichia jadinii intracellularly formed gold nanoparticles of spherical, triangular and hexagonal morphologies throughout the cell mainly in the cytoplasm, of size nm in 24 hr Their photosynthesis machinery has been evolved from cyanobacteria via endosymbiosis.
They are predominant primary producers in many aquatic environments. Among various algae, Chlorella sp. Chlorella vulgaris is a single-celled green algae belonging to phylum Chlorophyta, and the extracts of C. The dried algal cells were found to have a strong binding ability towards tetrachloroaurate III ions to form algal-bound gold, which was subsequently reduced to form Au 0.
Though chemical synthesis produces nanoparticles more rapidly with well-controlled shape, size and dispersity, the use of toxic and expensive chemicals as reducing and capping agents restricts its use in biomedical applications.
In that case, optimizing the conditions like pH, temperature and metal ions solute concentration for expediting the biological synthesis of nanoparticles with narrow size and shape is mandatory. To date, only very few reports have been documented on the optimization in biological processes. With an increase in the concentration of GSP, gold plates with lateral sizes up to micrometers were produced The study of heavy metal biosorption by various algae showed that brown algae are superior compared to other autotrophs and algae However the microbial mediated synthesis of nanoparticles is not industrially feasible as it requires expensive medium and maintenance of highly aseptic conditions.
Hence, exploration of the plant systems as the potential bio-factories has gained heightened interest in the biological synthesis of nanoparticles. Hence, exploration into plant systems has been considered to be a potential bioreactor for synthesis of metal nanoparticles without using toxic chemicals. Recently, we have reported that the various plant materials such as Rosmarinus officinalis 30 , Sesbania grandiflora 31 , Tribulus terrestris 32 , used for biological synthesis of silver and gold nanoparticles.
In continuation of the efforts for synthesizing gold nanoparticles by green route, here we present a report on the facile, rapid, and single pot aqueous biosynthesis of these nanoparticles using leaf extract of S.
The literature survey revealed that they are rich in various active ingredients such as water soluble antioxidant polyphenols, flavonoids etc, and research is still underway. They need to be provided with energy for their survival. Human cancer cells and non-cancerous cells intracellularly produced some metal nanoparticles in vitro conditions that mimic their natural cellular environment.In , Richard Feynman gave a talk describing molecular machines built with atomic precision. At the nanoparticle-liquid interface, polyelectrolytes have been utilised to modify surface properties and the interactions between particles and their environment. For example, current advances being made with nanoparticles promise to significantly improve signal generation and detection in high throughput, multiplexed biological assays.
Consequently, the advantages of plant-mediated preparation of metal nanoparticles lead researchers to in search of further exploration of the bio-reduction mechanism of metal ions by plants and the possible mechanism of formation of metal nanoparticle in and by the plants Ahmad and Sharma Besides, nanotechnology also leads an alternative technological pathway for the exploration and revolution of biological entities, whereas biology provides role models and biosynthetic constituents to nanotechnology. In Japan, Sugibayashi et al. Van Hyning and Zukoski, In the milling process, material is selectively removed from the substrate, usually a metal sheet, forming a cavity with certain geometries.
At higher flux, the material is converted to plasma.
FDA, Furthermore, some studies demonstrate the good stability of capped biopolymer-AgNPs. All rights reserved.
To date, the weight researchers must place on ion release when discussing AgNP toxicity is still a difficult concept to discern. Molecules with low molar mass have been used as stabilizing agents Warner et al. EPA has developed reporting and recordkeeping requirements for companies that manufacture or process nanoscale chemical substances. Studies such as these allow researchers to understand the behavior of AgNPs in real-world scenarios as well as to aid risk assessments. Due to the attractive physical and chemical properties of silver at the nanoscale, the development of silver nanoparticles is expanding in recent years and is nowadays significant for consumer and medical products. The use of this noxious weed has an added advantage in that it can be used by nanotechnology processing industries Parashar et al.
For example, Miller and Wickson and Patenaude et al. Human cancer cells and non-cancerous cells intracellularly produced some metal nanoparticles in vitro conditions that mimic their natural cellular environment. Nanotechnologies kick in right in time.
Further experimental modeling of assays is needed in order to implement standardized air and aquatic screening for AgNPs.
With an increase in the concentration of GSP, gold plates with lateral sizes up to micrometers were produced Chemical methods for the synthesis of monodisperse and quasi-spherical AgNPs in liquid phase. Klaus et al.
Nanotechnology emerges from the physical, chemical, biological and engineering sciences where, novel techniques are being developed to probe and manipulate single atoms and molecules. The drawbacks of low production rate, structural particle deformation, and inhibition of particle growth are also encountered in these nanoparticles synthesis.
Selective chemical reactivity is quite common with nanocomposites, which gives the potential for disintegration of the material into one or the other component. Generally, the bio-reduction mechanism of metal nanoparticle in plants and plant extracts includes three main phases Makarov et al. One of the pioneers in this field was Professor Peter Paul Speiser. An illustration of some selected surface chemistries and conjugation strategies that are applied to NPs. Experimental data showed that watermelon absorbed iron from nano-ferric oxide, and nano-ferric oxide promoted watermelon growth in some ways in a suitable concentration.
Studies have provided compelling evidence that the interaction of AgNPs with biological media and biomolecules is complicated and can lead to particle agglomeration, aggregation, and dissolution Stebounova et al. The intracellular synthesis of gold nanoparticles produced by V.
Ag and AgNP composites have found use in the control of various phytopathogens as well as for plant disease management Liu et al. The biosensor market can be broken down to three basic categories: diagnostics for clinical and research use, nutritional and consumer product safety and chemical and biological warfare defense.