Characterization of Nanoparticles

The method chosen for the characterization of nanoparticies depends on sample type, data required, quantitative or qualitative analysis and cost of analysis involved in the experiment. The type of the sample greatly affects the method chosen because some methods may require the sample in a liquid form and others may require solid suspension still others may go well with both types. One must ensure that the sample is not decomposed or it does not consist of any chemical species that may get denatured like proteins with any of the physical or chemical treatment used in the technique. Especially when stud nng nanocomplexes or nanocomposites that contain proteins immobilized on their surfaces, proteins may be unable to withstand high temperature or any other conditions used in the treatment and may decompose and lose their activity. Ideally there is no single method that is used for characterizing nanoparticies. Results from several methods are clubbed together to acquire complete information regarding physical and chemical aspects of nanoparticies. The following techniques have been successfully used for measurement of particle size and related dimensions of nanoparticies. 

Transmission Electron Microscopy (TEM] pi] Scanning Electron Microscopy (SEM] 

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The most important information about the nanoparticles is the size, shape, and their distributions which crucially influence physical and chemical properties of nanoparticles. TEM is a powerful tool for the characterization of nanoparticles. TEM specimen is easily prepared by placing a drop of the solution of nanoparticles onto a carbon-coated copper microgrid, followed by natural evaporation of the solvent. Even with low magnification TEM one can distinguish the difference in contrast derived from the atomic weight and the lattice direction. Furthermore, selective area electron diffraction can provide information on the crystal structure of nanoparticles. 

As the reader might have noticed, many conclusions in electrocatalysis are based on results obtained with electrochemical techniques. In situ characterization of nanoparticles with imaging and spectroscopic methods, which is performed in a number of laboratories, is invaluable for the understanding of PSEs. Identification of the types of adsorption sites on supported metal nanoparticles, as well as determination of the influence of particle size on the adsorption isotherms for oxygen, hydrogen, and anions, are required for further understanding of the fundamentals of electrocatalysis. 

The physicochemical characterization of a colloidal carrier is necessary because important characteristics, such as particle size, hydrophobicity, and surface charge, determine the biodistribution after administration [129-132]. Preparation conditions, such as the pH of the polymerization medium, monomer concentration, and surfactant concentration, can influence the physicochemical characteristics of the particles [60, 62, 64]. It is, therefore, essential to perform a comprehensive physicochemical characterization of nanoparticles, which has been reviewed by Magenheim and Benita [133]. 

Chromatographic approaches have been also used to separate nanoparticles from samples coupled to different detectors, such as ICP-MS, MS, DLS. The best known technique for size separation is size exclusion chromatography (SEC). A size exclusion column is packed with porous beads, as the stationary phase, which retain particles, depending on their size and shape. This method has been applied to the size characterization of quantum dots, single-walled carbon nanotubes, and polystyrene nanoparticles [168, 169]. Another approach is hydro-dynamic chromatography (HDC), which separates particles based on their hydro-dynamic radius. HDC has been connected to the most common UV-Vis detector for the size characterization of nanoparticles, colloidal suspensions, and biomolecules [170-172]. 

Many analytical tools are theoretically suitable for the characterization of nanoparticles, but requirements for analysis of engineered nanoparticles in natural and food-related samples will differ greatly from their analysis in pure media. At the moment, analytical methods are required to reliably detect and characterize nanoparticles in complex matrices, such as foodstuff. 

Anal, A.K., Tobiassen, A., Flanagan, J., Singh, H. (2008). Preparation and characterization of nanoparticles formed by chitosan-caseinate interactions. Colloids and Surfaces B Biointerfaces, 64, 104-110. 

UV-visible spectra of nanoparticles arise from two sources. The first, more general source is simple Rayleigh scattering that gives rise to the monotonic increase in absorption as wavelength decreases [33]. Au and Ag nanoparticles have intense surface plasmon bands that are valuable additional spectroscopic tools [33-35]. These bands, which arise from a concerted oscillation of nanoparticle electrons, shift with particle size and composition, and are therefore useful handles for the physical characterization of nanoparticle composition. 

Passirani, C., L. Ferrarini, et al. (1999). Preparation and characterization of nanoparticles bearing heparin or dextran covalently-linked to poly(methyl methacrylate). J Biomater Sci Polym Ed 10(1) 47-62. 

Shukla, A. Kiselev, M.A. Hoell, A. Neubert, R.H.H. Characterization of nanoparticles of lidocaine in w/o microemulsions using small-angle neutron scattering and dynamic light scattering. Pramana-Journal of Physics... 

The hydrophilicity of the nanoparticle surface can be evaluated by hydrophobic interaction chromatog-raphy. This technique, based on affinity chromatography, allows a very rapid discrimination between hydrophilic and hydrophobic nanoparticles. The nanoparticles are passed through a column containing a hydrophobic interaction chromatography gel. The nanoparticles that are retained by the gel and only eluted after the addition of a surfactant are considered as hydrophobic, whereas the nanoparticles that do not interact with the gel and that are directly eluted from the column are considered as hydrophilic. Apart from the hydrophobic interaction chromatography, the field flow fractionation techniques recently appeared to present interesting potential for the characterization of nanoparticles with different surface characteristics. ... 

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