Nanobiotechnology: Basic and Applied Aspects
162
Nanobiotechnology: Basic and Applied Aspects
162Hardcover
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Product Details
| ISBN-13: | 9781783087372 |
|---|---|
| Publisher: | Anthem Press |
| Publication date: | 09/01/2017 |
| Pages: | 162 |
| Product dimensions: | 6.00(w) x 9.00(h) x 1.00(d) |
About the Author
Samrat Roy Choudhury is currently engaged as a Research Associate in the Myeloma Institute at the University of Arkansas for Medical Sciences. He was an alumnus of Purdue University, USA and Indian Statistical Institute, India, where he pursued his postdoctoral training (2013-2016) and earned his PhD degree (Biotechnology) respectively. He has several peer-reviewed articles, patents, book chapters and a book entitled “Antibiotic resistance in E.coli and K. pneumoniae spells neonatal death (ISBN: 978-9380601328); published by LAP Lambert Academic Publishing” to his credit. Dr. Roy Choudhury has been awarded with the Best Scientist Award in Biotechnology at the 18th State Science and Technology Congress (2011) organized by the West Bengal State Govt., India.
Read an Excerpt
CHAPTER 1
AN INTRODUCTION TO THE SCOPE OF NANOSCIENCE AND NANOTECHNOLOGY
Indrani Roy and Arunava Goswami
The Greek word for dwarf is "Nano." The first mention of some of the distinguishing concepts in nanotechnology (but predating use of that name) was in 1867 by James Clerk Maxwell, when he proposed a tiny entity known as Maxwell's Demon, able to handle individual molecules, as a thought experiment. The first observations and size measurements of nano-particles were made during the first decade of the twentieth century. They are mostly associated with Richard Adolf Zsigmondy, who made a detailed study of gold sols and other nanomaterials, with sizes as low as 10 nm and less. He published a book in 1914, and used an ultramicroscope that employs the dark field method for seeing particles with sizes much less than light wavelength. Zsigmondy was also the first to use the term nanometer explicitly for characterizing particle size. He determined it as 1/1,000,000 of a millimeter. He developed the first system classification based on particle size in the nanometer range.
More significant developments in characterizing nanomaterials took place in the second half of the twentieth century. The prefix "nano" was officially recognized in 1956. The first use of the concepts found in "nanotechnology" was in a talk given by physicist Richard Feynman on December 29 1959. Feynman described a process by which the ability to manipulate individual atoms appeared plausible.
The term "nanotechnology" was defined by Tokyo Science University professor Norio Tanuguchi in a 1974 paper as follows: "'Nano-technology' mainly consists of the processing of, separation, consolidation, and deformation of materials by one atom or by one molecule." In the 1980s, the basic idea of this definition was explored in greater depth by Dr K. Eric Drexler, who promoted the technological significance of nano-scale phenomena and devices through speeches and the books Engines of Creation: The Coming Era of Nanotechnology (1986) and Nanosystems: Molecular Machinery, Manufacturing, and Computation, after which the term acquired its current sense. Engines of Creation is considered the first book on the topic of nanotechnology. Nanotechnology and nanoscience got started in the early 1980s with two major developments: the birth of cluster science and the invention of the scanning tunneling microscope (STM). This development led to the discovery of fullerenes in 1985 and carbon nanotubes a few years later. In another development, the synthesis and properties of semiconductor nanocrystals was studied. This led to a fast increasing number of metal and metal oxide nanoparticles and quantum dots. The atomic force microscope (AFM or SFM) was invented six years after the STM, and made possible the visualization of nanomaterials (Fig. 1). Don Eigler moved the first individual atom twenty years ago, and shortly afterward he wrote IBM's name with 35 Xenon atoms (Fig. 2). Moving atoms had big consequences in that it made the idea of assembling devices atom by atom very real. IBM has built on that nanotechnology foundation, storing information on specific gold atoms, collecting carbon monoxide molecules into computer logic circuits, and pursuing a vision for vastly more compact computing technology.
The following illustration, titled "The Scale of Things," created by the US Department of Energy, provides a comparison of various objects to help you begin to envision exactly how small a nanometer is. The chart starts with objects that can be seen by the unaided eye, such as an ant, and progresses to objects about a nanometer or less in size, such as the ATP molecule used in all living systems to store energy from food (Fig. 3).
Now that you have an idea of how small a scale nanotechnologists work with, consider the challenge they face. Such an image helps you imagine the problem scientists have while working with nanoparticles.
Sometimes a distinction is made between nanotechnology and nanoscience, the latter focusing on the observation and study of phenomena at the nanometer scale. The distinction is not of great importance. Nanoscience suggests a solid body of theory upon which a technology can be built. Such theory is still inchoate, however, and the nanotechnologist is as likely to contribute to it as the nanoscientist. It is best to use the term "nanotechnology" in an all-embracing sense (Fig. 4, Fig. 5).
Although nanoparticles are generally considered an invention of modern science, they actually have a very long history. Humans have unwittingly employed nanotechnology for thousands of years, for example in making steel, paintings and in vulcanizing rubber. The best known surviving example is the Lycurgus Cup from the Roman Empire, fourth century AD. The cup glows red or green depending on whether light is transmitted or reflected from the cup. The effect was achieved by mixing minute amounts of silver and gold in the glass. Pottery from the Middle Ages and Renaissance often retains a distinct gold or copper-colored metallic luster. This so-called luster is caused by a metallic film applied to the transparent surface of a glazing. The luster can still be visible if the film has resisted atmospheric oxidation and other weathering. The luster originates within the film itself, which contains silver and copper nanoparticles dispersed homogeneously in the glassy matrix of the ceramic glaze. These nanoparticles were created by artisans by mixing copper and silver salts and oxides together with vinegar, ochre and clay on the surface of previously-glazed pottery. The object was then placed into a kiln and heated to about 600°C in a reducing atmosphere. In the heat, the glaze would soften, causing the copper and silver ions to migrate into the outer layers of the glaze. There, the reducing atmosphere reduces the ions back to metals, which then come together forming the nanoparticles that give the color and the optical effects (Fig. 6).
Luster technique showed that ancient craftsmen had a rather sophisticated empirical knowledge of materials. Carbon black is the most famous example of a nanoparticulate material that has been produced in quantity for millennia. It was used to make "Wootz" steel, high-grade steel that was highly prized and much sought-after across several regions of the world for over nearly two millennia. Wootz steel is characterized by a pattern of bands or sheets of micro carbides. It was developed in India around 300 BC. There is archaeological evidence of the manufacturing process in South India from that time. Wootz steel was widely exported and traded throughout ancient Europe and the Arab world. It became particularly famous in the Middle East, where it was known as Damascus steel. Studies have found existence of carbon nanoparticles in the famous sword of Tipu Sultan and the Ajanta Paintings (Fig. 7, Fig. 8).
70% of carbon black now produced is used as a pigment and in the reinforcing phase in manufacturing automobile tires. Carbon black also helps conduct heat away from the tread and belt area of the tire, reducing thermal damage and increasing tire life. Carbon black particles are also employed in some radar-absorbent materials and in photocopier and laser printer toner.
Michael Faraday provided the first description, in scientific terms, of the optical properties of nanometer-scale metals in his classic 1857 paper [Faraday Michael (1857). "Experimental relations of gold (and other metals) to light". Phil. Trans. Roy. Soc. London 147: 145–181.] In a subsequent paper, Turner [Turner, T. (1908). "Transparent Silver and Other Metallic Films". Proc. Roy. Soc. Lond. A 81 (548): 301–310] points out that:
"It is well known that when thin leaves of gold or silver are mounted upon glass and heated to a temperature which is well below a red heat (~500°C), a remarkable change of properties takes place, whereby the continuity of the metallic film is destroyed. The result is that white light is now freely transmitted; and reflection is correspondingly diminished, while the electrical resistivity is enormously increased."
The transition from microparticles to nanoparticles can lead to a number of changes in physical properties. Two of the major factors in this are the increase in the ratio of surface-area-to-volume, and the size of the particle moving into the realm where quantum effects predominate. The increase in the surface-area-to-volume-ratio, which is a gradual progression as the particle gets smaller, leads to an increasing dominance of the behavior of atoms on the surface of a particle over that of those in the interior of the particle. This affects both the properties of the particle in isolation and its interaction with other molecules. Nanoparticles are of great scientific interest as they are effectively a bridge between bulk materials and atomic or molecular structures. A bulk material should have constant physical properties, regardless of its size. But at the nano-scale, size-dependent properties are often observed. Thus the properties of materials change as their size approaches the nanoscale and as the percentage of atoms at the surface of a material becomes significant. For bulk materials larger than one micrometer (or micron), the percentage of atoms at the surface is insignificant in relation to the number of atoms in the bulk of the material. The interesting and sometimes unexpected properties of nanoparticles are therefore largely due to the large surface area of the material, which dominates over the contributions made by the small bulk of the material. Nanoparticles often possess unexpected optical properties as they are small enough to confine their electrons and produce quantum effects. For example, gold nanoparticles appear deep red to black in solution. Nanoparticles of usually yellow gold and gray silicon appear red in color. Gold nanoparticles melt at much lower temperatures (~300°C for 2.5 nm size) than the gold slabs (1064°C). Absorption of solar radiation in photovoltaic cells is much higher in materials composed of nanoparticles than it is in thin films of continuous sheets of material, i.e. the smaller the particles, the greater the solar absorption. Other size-dependent property changes include quantum confinement in semiconductor particles, surface plasmon resonance in some metal particles and superparamagnetism in magnetic materials. Ironically, the changes in physical properties are not always desirable. Ferromagnetic materials smaller than 10 nm can switch their magnetization direction using room temperature thermal energy, thus making them unsuitable for memory storage. Suspensions of nanoparticles are possible since the interaction of the particle surface with the solvent is strong enough to overcome density differences, which otherwise usually result in a material either sinking or floating in a liquid. High surface area is a critical factor in the performance of such technologies as fuel cells and batteries. The huge surface area of nanoparticles also results in a lot of interactions between the intermixed materials in nanocomposites, leading to special properties such as increased strength and/or increased chemical/heat resistance. The fact that nanoparticles have dimensions below the critical wavelength of light renders them transparent. This transparency makes them useful for applications in packaging, cosmetics and coatings.
Some of the properties of nanoparticles may not be predicted simply by understanding the increasing influence of surface atoms or quantum effects. It has been recently shown that perfectly formed silicon nanospheres, with diameters of between 40 and 100 nm, are not just harder than silicon but among the hardest materials known, falling between sapphire and diamond.
What is New in Nanotechnology?
Nanoscience has been present all along in the traditional disciplines of Chemistry, Biology and Physics. Chemistry is a powerful contender for claiming nanotechnology under its domain. Chemistry deals with the manipulation of molecules and hence is familiar with nanometer dimensions. However the chemist does not control systems in the way the engineer does. Molecules mostly reside in their free energy minima and it requires special ingenuity, intuition and luck to steer their precursors along the paths to the desired end product.
Physics provides the answers to the questions raised by the special properties of matter at nano scale. Size is mostly a relative term, but quantum mechanics offers a definition of absolute smallness: a system is absolutely small if it is perturbed by the act of observing it. Thus a photon is usually destroyed by the act of observation, or its state is irretrievably altered. Most nanosystems are not small enough for this to be the case. Nevertheless, quantum effects are needed to understand certain nano-objects, for example, the small clusters of atoms called quantum dots, nanodots or nanoparticles. These objects are tiny spheres of a solid, typically a semiconductor. In condensed matter, electrons are no longer the point particles that they are believed to be in free space, but have extension, quantified by their Bohr radius, which can vary from a few to hundreds of nanometers, depending on the material. It is possible to make nanoparticles smaller than the Bohr radius of electrons in them. Thus the electrons are subjected to quantum confinement, with the observable effect that the optical absorption and fluorescent emission of the particle are shifted towards higher energies, the magnitude of the shift depending on the particle size. Additionally, a number of physical (mechanical, electrical, optical, etc.) properties change when compared to macroscopic systems. One example is the increase in surface-area-to-volume ratio altering mechanical, thermal and catalytic properties of materials. Quantum effects must also be considered with ultra-miniaturized electron circuitry-single electron devices. Much of the fascination with nanotechnology stems from these quantum and surface phenomena that matter exhibits at the nanoscale.
Biology is considered to provide living proof of the principle of nanotechnology-nanomechanical devices, nanoreactors, nanosensors and nanoassemblers. Biological structures at macromolecular and supramolecular scales are apparently assembled using the principles of self-assembly. These structures, mostly protein based, often combine extraordinary lightness with extraordinary strength. Two amazing examples are the FATPase enzyme that uses a proton gradient across the cell membrane in which it is embedded to synthesise ATP, and the Type III Secretion System (TTSS) — a spherical assembly of needles found on the surface of certain pathogenic bacteria and used to inject toxins into their targets.
Physics, chemistry and biology strongly overlap with nanoscience, but differ essentially from nanotechnology, which seeks to impose control over materials and devices at this scale. Nanoscience and nanotechnology could therefore be defined via the convergence of chemistry, biology, physics and engineering.
Key Elements of Nanotechnology
The technology of realization can be conveniently divided into fabrication and metrology. While fabrication is dealt with here, metrology is discussed in the next chapter.
There is a wide variety of techniques for fabricating nanoparticles. These essentially fall into three categories. The first two are "bottom-up" approaches while the third is a "top-down" method of making nanoparticles.
Condensation from a vapor: This method is used to make metallic and metal ceramic nanoparticles. It involves evaporation of a solid metal followed by rapid condensation to form nanosized clusters that settle in the form of a powder. Various approaches to vaporizing the metal can be used and variation of the medium into which the vapor is released affects the nature and size of the particles. Inert gases are used to avoid oxidation when creating metal nanoparticles, whereas a reactive oxygen atmosphere is used to produce metal oxide ceramic nanoparticles. Final particle size is controlled by variation of parameters such as temperature, gas environment and evaporation rate.
Chemical synthesis: This consists of growing nanoparticles in a liquid medium composed of various reactants. This is typified by the sol-gel approach and is also used to create quantum dots. Chemical techniques are generally better than vapor condensation techniques for controlling the final shape of the particles. The ultimate size of the nanoparticles might be dictated, as with vapor condensation approaches, by stopping the process when the desired size is reached, by choosing chemicals that are stable and stop growing at a certain size. The approaches are generally low-cost and high-volume, but contaminations from the precursor chemicals can be a problem. This can interfere with one of the common uses of nanoparticles — sintering — to create surface coatings.
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