Biological cells Composition

TOF-SIMS has important potentials in many areas of life science, in fundamental and applied research as well as in product development and control. This holds for the characterization of biological cells and tissues, of sensor and microplate arrays, of drug delivery systems, of implants, etc. In all these areas, relevant surfaces feature a very complex composition and structure, requiring the parallel detect ion of many different molecular species as well as metal and other elements, with high sensitivity and spatial resolution requirements, which are exactly met by TOF-SIMS. 

The lipid molecule is the main constituent of biological cell membranes. In aqueous solutions amphiphilic lipid molecules form self-assembled structures such as bilayer vesicles, inverse hexagonal and multi-lamellar patterns, and so on. Among these lipid assemblies, construction of the lipid bilayer on a solid substrate has long attracted much attention due to the many possibilities it presents for scientific and practical applications [4]. Use of an artificial lipid bilayer often gives insight into important aspects ofbiological cell membranes [5-7]. The wealth of functionality of this artificial structure is the result of its own chemical and physical properties, for example, two-dimensional fluidity, bio-compatibility, elasticity, and rich chemical composition. 

The benefit of the LbL technique is that the properties of the assemblies, such as thickness, composition, and function, can be tuned by varying the layer number, the species deposited, and the assembly conditions. Further, this technique can be readily transferred from planar substrates (e.g., silicon and quartz slides) [53,54] to three-dimensional substrates with various morphologies and structures, such as colloids [55] and biological cells [56]. Application of the LbL technique to colloids provides a simple and effective method to prepare core-shell particles, and hollow capsules, after removal of the sacrificial core template particles. The properties of the capsules prepared by the LbL procedure, such as diameter, shell thickness and permeability, can be readily adjusted through selection of the core size, the layer number, and the nature of the species deposited [57]. Such capsules are ideal candidates for applications in the areas of drug delivery, sensing, and catalysis [48-51,57]. 

Electron probe and X-ray fluorescence methods of analysis are used for rather different but complementary purposes. The ability to provide an elemental spot analysis is the important characteristic of electron probe methods, which thus find use in analytical problems where the composition of the specimen changes over short distances. The examination of the distribution of heavy metals within the cellular structure of biological specimens, the distribution of metal crystallites on the surface of heterogeneous catalysts, or the differences in composition in the region of surface irregularities and faults in alloys, are all important examples of this application. Figure 8.45 illustrates the analysis of parts of a biological cell just 1 pm apart. Combination of electron probe analysis with electron microscopy enables visual examination to be used to identify the areas of interest prior to the analytical measurement. 

Membranes play an important role in natural science and for many technical applications. Depending on their purpose, their shape can be very different. For instance, membranes include porous or non-porous films, either supported or non-supported, with two interfaces surrounded by a gas or by a liquid. Important properties of non-porous membranes are their permeability for certain compounds and their stability. In biological cells their main task is to stabilize the cell and to separate the cell plasma from the environment. Furthermore, different cells and cell compartments have to communicate with each other which requires selective permeability of the membranes. For industrial applications membranes are often used for separation of gases, liquids, or ions. Foams and emulsions for instance are macroscopic composite systems consisting of many membranes. They contain the continuous liquid phase surrounded by the dispersed gas phase (foams) or by another liquid (emulsions). Beside these application possibilities membranes give the opportunity to investigate many questions related to basic research, e.g. finite size effects. 

Are there statistically significant and/or biologically relevant changes in the magnitude, time course, or cell composition of the DTH reaction in drug-treated animals compared to vehicle-control animals ... 

The high spatial resolution is utilized in CARS microscopy, which is mainly applied to the investigation of biological cells and their compositions (see Sect. 3.4.3). 

Thus, bioadhesion is sensitive to factors of electrical and compositional nature. This offers various ways to manipulate cell adhesion, for example, by changing the pH and/or ionic strength of the medium and by adding adsorbing or nonadsorbing polymer molecules of different sizes. These possibilities can be exploited for immobilization of biological cells in bioreactors, for bioremediation of soils and sediments, and for many other applications. 

When the sequential layer growth is proofed for certain multilayer composition one can apply these conditions to fabricate the multilayer film on surface of the colloidal particles with different size and shape discrepancy such as biological cells [40,41], dye nanocrystals [42,43] or protein aggregates [44]. 

Other ways in which the Ca P ratio could be caused to depart from the ideal include (1) the presence of an additional crystalline compound, octacalcium phosphate, whose unit cell composition is Ca8(HP04)2(P04)4-5H20 and whose Ca P ratio is 1 3-3, giving rise to the possibility that biological mineral may be an intercrystalline mixture (2) substitution of other ions for calcium in the crystal lattice. For example, hydroxyapatites prepared by precipitation from solutions of different pH have different Ca P ratios. Substitution of hydronium ions for calcium ions causes a decrease in the Ca P ratio (3) adsorption of excess phosphate or calcium phosphate complexes on to the crystal surface. 

Isolated biological cells or cell fragments (e.g. membrane particles) have been used as receptor layers in biosensors. Such compositions allow interesting experiments, but they are not suited as a basis for commercial sensors. 

One reason to develop liposome electroformation was to establish a method for tire preparation of unilamellar cell-sized vesicles of a particular lipid composition, and thereby imitate biological cells with respect to their mechanical and electric properties. This could then be used for the direct optical microscopy model study of membrane interactions. 

Metal Composition in Biological Cells and Tissues, Anal. Bioanal. Chem.,... 

The past decades have seen a incredible boost of carbon nanotubes (CNTs) in both scientific research and commercial sectors since lijima s discovery of CNTs [117]. CNTs have extraordinary and unique mechanical, optical and electrical properties and major research efforts were focused on areas including high performance electroiucs, scanning probe microscopy, fuel cells, composites, mechanical, chemical, biological and physical sensors, etc. [118]. However, the formation of insoluble large bundles, caused by the strong van der Waals interactions between individual hydrophobic nanotubes, limited the applications of CNTs. In order to harness the full potential of CNTs, their separation and dispersion are therefore an intense subject of scientific research. 

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