Naturally Occurring Nanoparticles

Broadly speaking, nanoparticles can be classified into two major categories  

Natural processes such as volcanic eruptions, sea sprays, and mineral deposits give rise to everyday-occurring nanoparticles present as nanosuspensions in the atmosphere. They result in the formation of chemical transformants of metallic or non-metallic origin, which is becoming major issue of concern worldwide. These transformants accumulate in the form of nanodeposits on soil, water, or land surfaces, which may pose threat to life owing to 

For exampie, studies have been conducted on viruses such as adenovirus [20], hepatitis 8 virus, cowpea virus [21], and bacteriophages [22] and piant viruses such as potato virus X [PVX] [23] and tobacco mosaic virus [TMV] [24]. Many virus-iike particies have aiso been studied that behave more or iess iike viruses oniy and are used to make conjugate compiexes in vaccine deveiopment. For instance, hepatitis B core [HBc] virus-iike particie with the diameter of 30-34 nm has been prepared by genetic modifications is used as an effective immune stimuiant [25]. 

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The casein micelle is an example of a naturally occurring nanoparticle formed when the different types of caseins (asl, 0 2, (5, and k) self-assem-ble around amorphous calcium phosphate. This allows it to be a natural carrier for calcium. The casein micelle also serves as a carrier for hydro-phobic bioactives (Livney and Dalgleish, 2007). Treatments such as ultra-high pressure have been reported to alter the structural characteristics of the casein micelle by partially removing parts of the surface of the casein (Sandra and Dalgleish, 2005). Altering the surface properties of these nanoparticles is expected to alter their functional properties. 

There are naturally occurring nanoparticles in soot and volcanic ash, and nanoparticles have been used since the Middle Ages to color stained glass. When used in products, nanomaterials can be either free or fixed. Free nanomaterials are in solution or suspension, and are in products such as sunscreens and fuels. Fixed nanomaterials are in composites such as resins... 

Incorporation of nanofrllers into polymer matrix has been proved to be a powerful tool in order to increase the polymer properties (Lin et al. 201 la, b). It is widely accepted that addition of nanofrller into bio-based matrixes in order to fabricate nano-biocomposite materials could be a powerful solution to improve these properties (Alexandre and Dubois 2000 Bordes et al. 2009 Sinha Ray and Okamoto 2003). Studies on mbular silica-based naturally occurring nanoparticles as reinforcing material is still new (Ismail et al. 2008 Prashantha et al. 2011). Halloysite particles are readily obtainable and are much cheaper than other nanoparticles such as CNTs. More importantly, the unique crystal structure of HNTs resembles that of CNTs, and therefore halloysite particles may have the potential to provide cheap alternatives to expensive CNTs because of their mbular stmcture in nanoscale. Moreover, due to its similarity to other layered clay minerals such as MMT, halloysite has the potential to be further intercalated or exfoliated chemically or physically (Tang et al. 2011). 

The activity of enzymes allows for rapid accumulation of insoluble ferric iron aqueous species in solutions where inorganic reactions would occur slowly or not at all. The reaction kinetics may impact the nature of nanoparticles produced (composition, structure, defect structure). However, it should be noted that the crystallization reaction itself is not enzyme mediated and the reaction often does not occur within or on the cell wall. Ferric iron ions diffuse out of the periplasm to form molecular clusters and/or nanoparticles in solution. The precipitation mechanisms probably differ only slightly from those involved in inorganic reactions. 

Characterization of naturally occurring and synthetic nanoparticles in order to determine the variation in bulk and surface structure and properties with particle size. 

Naturally occurring nanomaterials exist in a variety of complex forms. In this chapter a short set of definitions will be stated for clarity. Nanocrystals are single crystals with sizes from a few nm up to about 100 nm. They may be aggregated into larger units with a wide spectrum of microstructures. Nanoparticles are units of minerals, mineraloids or solids smaller in size than 100 nm, and composed of aggregated nanocrystals, nanoclusters or other molecular units, and combinations of these. Nanoclusters are individual molecular units that have well-defined structure, but too small to be true crystals. Al and ZnsSs solution complexes are types of nanoclusters with sizes from sub nanometer to a few nm. Nanoporous materials are substances with pores or voids of nanoscale dimensions. These materials can be single crystals, such as zeolites or... 

Nanoparticles and the Environmenf targets naturally occurring, finely particulate minerals, many of which form at low temperature. Thus, many of the compounds of interest are those of the clay fraction . Of course, there have been decades of critical work on the structures, microstructures, and reactivity of finely crystalline or amorphous minerals, especially oxides, oxyhydroxides, hydroxides, and clays. We will not summarize what is known in general about these (for this, the reader is referred to earlier Reviews in Mineralogy volumes). Rather, our goal is to focus on the features of these materials that stem directly or indirectly from their size. 

Solubility (in the molecular sense, rather than in the sense of forming dispersions and sols) opens up a number of possibilities. The first and perhaps most important, is that it allows size-selective precipitation [10], permitting monodisperse nanoparticles to be prepared. It is only when particles are monodisperse that their size-dependent physical properties can be studied in detail [6j. It is also possible to organize these monodisperse nanoparticles via slow evaporation to yield superlattices [11-13]. Superlattices of nanocrystals can rightly be described as a new class of materials, comprising crystals of crystals as opposed to most crystalline solids which are crystals of atoms [14]. In contrast, naturally occurring opals are crystals of amorphous silica spheres [15]. 

The focus of current scientific and regulatory activities is on engineered or synthetically produced substances with nanoscale dimensions. There are numerous naturally occurring nanoscale components of substances such as mineral deposits and volcanic dust, and in byproducts of common processes such as diesel exhaust and byproducts of coal combustion. Although exposure to these nanomaterials may be minimal and controlled in most cases, studies on such common nanomaterials as fog, coal dust, and ultrafine aerosols have provided useful information as to exposure and effects of particles this small, and these results are useful in predicting the properties of engineered nanoparticles. 

However, we have also some other colouristic needs - from a completely different area. Worldwide, 2,400,000 tonnes of salmon are grown annually in wire cages (Fig. 1.5). In order to ensure that fillets from this farmed salmon have the same colour as those from wild salmon, the farmed fish are fed the naturally occurring carotenoid dyestuff astaxanthin, in the form of amorphous nanoparticles, as part of their regular diet. 

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