Nanoparticles, definition

What makes a nanoparticle a nanoparticle Definitions of the size ranges for molecules, nanoparticles, and macroscopic solids must be compound specific. However, a useful upper limit for nanoparticles is the size at which one of its properties deviates from the value for the equivalent bulk material by an amount that is significantly larger than the error of the method used to make the measurement (a few percent). In practice, some characteristic will probably be different enough to warrant description as a hanoparticle if it is less than a few tens of nanometers in diameter, and perhaps less than a fraction of a micron in diameter. 

For PC = 193 atoms per one nanocluster (for = 20) is obtained. It is obvious that the indicated value corresponds well to the adduced above nanoparticle definition criterion N = 10 10 ) [9, 17]. 

The definition above is a particularly restrictive description of a nanocrystal, and necessarily limits die focus of diis brief review to studies of nanocrystals which are of relevance to chemical physics. Many nanoparticles, particularly oxides, prepared dirough die sol-gel niediod are not included in diis discussion as dieir internal stmcture is amorjihous and hydrated. Neverdieless, diey are important nanoniaterials several textbooks deal widi dieir syndiesis and properties [4, 5]. The material science community has also contributed to die general area of nanocrystals however, for most of dieir applications it is not necessary to prepare fully isolated nanocrystals widi well defined surface chemistry. A good discussion of die goals and progress can be found in references [6, 7, 8 and 9]. Finally, diere is a rich history in gas-phase chemical physics of die study of clusters and size-dependent evaluations of dieir behaviour. This topic is not addressed here, but covered instead in chapter C1.1, Clusters and nanoscale stmctures, in diis same volume. 

Clearly, the definitive characteristic of any nanoparticulate drug delivery system will be its submicrometer diameter. Sizing such particles in the suboptical region can be difficult as the measuring technique itself may alter size and properties by either hydrating or aggregating the particles. This will have a profound influence on the size of the particle [59]. Haskell [134] has discussed the various optical techniques available to measure the size of nanoparticles. 

A commonly used staining method for the cell nucleolus is based on silver nanoparticles [54], The proteins of the nucleolus, such as nucleolin, are known to have high affinity to silver ions due to their amino-terminal domain. Subsequent reduction leads to the formation of the silver nanoparticles stain. In spite of all the efforts, a general and definitive conclusion regarding the attraction between silver... 

To determine the phase properties of the calcined bimetallic nanoparticles, a detailed x-ray diffraction (XRD) study was carried out. The XRD data of AuPt/C showed that the diffraction patterns for the carbon-supported nanoparticles show a series of broad Bragg peaks, a picture typical for materials of limited structural coherence. Nevertheless, the peaks are defined well enough to allow a definitive phase identification and structural characterization. The diffraction patterns of Au/C and Pt/C could be unambiguously indexed into an fcc-type cubic lattice occurring with bulk gold and platinum. We estimated the corresponding lattice parameters by carefully determining... 

This review focuses on nanoparticles, namely objects that are roughly spherical. We use the commonly accepted definition for nanoscale objects of having a dimension below 100 nm, and so identify nanoparticles as objects with a diameter of 100 nm or smaller. The review does not focus on larger aspect ratio nanoscale materials such as nanotubes and nanorods, though they are mentioned in some cases. 

Increasingly chemists are contributing to the synthesis of advanced materials with enhanced or novel properties by using colloidal assemblies as templates. Colloid chemistry is particularly well suited to this objective since nanoparticles, by definition, are colloidal and since processing of advanced materials involve reactions at solid-solid, solid-liquid or solid-gas interfaces (3-5). 

Fig. 5.5. SERS image of mouse liver, a Whole-body map (1-mm steps) of nude mouse 2 h after tail vein injection of SERS nanoparticles. Most SERS particles accumulate in the liver (L, arrow), b Higher resolution (750 pm steps) and higher definition map of liver (arrow) showing organ detail including differentiation of the two liver lobes (reprinted with permission from [33]. Copyright 2008 National Academy of Sciences, USA)...

The answer is a definite yes. Ever since Mendeleyev transformed a simple list of elements into a useful scientific tool, the periodic table has been the doorway through which researchers of all kinds can explore the universe of matter. Old elements are put to new uses, like the zinc nanoparticles in sunscreen. Familiar reactions are found to create serious problems, such as the destruction of the ozone layer by chlorofluorocarbons. Like Mendeleyev himself, scientists are predicting the existence of brand-new elements that have never been seen but are certain to be built someday in the laboratory. 

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