Nanoparticles Particle Types

The chemical composition of particles can be just as varied as their shape. Commercial particles can consist of polymers or copolymers, inorganic constructs, metals and semiconductors, superparamagnetic composites, biodegradable constructs, and synthetic dendrimers and dendrons. Often, both the composition of a particle and its shape govern its suitability for a particular purpose. For instance, composite particles containing superparamagnetic iron oxide typically are used for small-scale affinity separations, especially for cell separations followed by flow cytometry analysis or fluorescence-activated cell sorting (FACS). Core-shell semiconductor particles, by 

The original polymeric latex particles still are widely used for separation and detection. Polymers provide a matrix that can be swollen for embedding other molecules in their core, such as organic dyes or fluorescent molecules. Even nanoparticle quantum dots can be incorporated into larger latex particles to form highly fluorescent composite microparticles. 

Dyed particles also are commonly used in diagnostic lateral flow tests (like the common home pregnancy test), as the colors can be seen with the eye without the need for special detectors. In this type of assay, antibodies or antigens are coupled to the dyed particles and a sample solution applied to the test strip carries them along within a membrane. The particles then are captured at points in the membrane that represent either a control or a positive sample result. Large numbers of color particles docking at these points within the membrane create the visual lines associated with these disposable tests. 

Polymeric particles can be constructed from a number of different monomers or copolymer combinations. Some of the more common ones include polystyrene (traditional latex particles), poly(styrene/divinylbenzene) copolymers, poly(styrene/acrylate) copolymers, polymethylmethacrylate (PMMA), poly(hydroxyethyl methacrylate) (pHEMA), poly(vinyltoluene), poly(styrene/butadiene) copolymers, and poly(styrene/vinyltoluene) copolymers. In addition, by mixing into the polymerization reaction combinations of functional monomers, one can create reactive or functional groups on the particle surface for subsequent coupling to affinity ligands. One example of this is a poly(styrene/acrylate) copolymer particle, which creates carboxylate groups within the polymer structure, the number of which is dependent on the ratio of monomers used in the polymerization process. 

Inorganic particles are used extensively in various bioapplications, too. Gold nanoparticles long have been used as detection labels for immunohistochemical (IHC) staining and lateral flow diagnostic testing. These dark, dense particles provide single particle detection capability 

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The reactions used for coupling affinity ligands to nanoparticles or microparticles basically are the same as those used for bioconjugation of molecules or for immobilization of ligands onto surfaces or chromatography supports. However, with particles, size can be a major factor in how a reaction is performed and in its resultant reaction kinetics. Since particle types can vary from the low nanometer diameter to the micron size, there are dramatic differences in how such particles behave in solution and how the density of reactive groups or functional groups affects reactions. 

The following sections discuss many of the major particle types and provide bioconjugation options for the coupling of ligands to the surface of functionalized particles. Some additional nanoparticle constructs, including gold particles, dendrimers, carbon nanotubes, Buckyballs and fullerenes, and quantum dots are discussed more fully elsewhere (see Chapter 7 Chapter 9, Section 10 Chapter 15 and Chapter 24). 

Microspheres and nanoparticles often consist of biocompatible polymers and belong either to the soluble or the particle type carriers. Besides the aforementioned HPMA polymeric backbone, carriers have also been prepared using dextrans, ficoll, sepharose or poly-L-lysine as the main carrier body. More recently alginate nanoparticles have been described for the targeting of antisense oligonucleotides [28]. As with other polymeric carrier systems, the backbone can be modified with e.g. sugar molecules or antibody fragments to introduce cellular specificity. 

The combination of fluorophores and suspended colloid particles could be used in metal-enhanced solution assays. Scheme 8.1 depicts the use of fluorophores and suspended colloid particles. Previous studies on fluorescence intensity enhancement between fluorophores and suspended particles in terms of metal core of nanoparticles, fluorophore type, and spacer used are summarized in Table 8.2. 

The compositions of nanoparticles in Houston differ markedly from those observed in Atlanta. In particular, the dominant composition in Houston is a Si-based particle rather than an organic type (Phares et al. 2001b). The Si particle type is also prevalent... 

A magnetic nanoparticle-to nucleic acid w/w ratio of 0.5 to 1 has proven useful for both DNA and siRNA lipoplexes and polyplexes with a variety of magnetic nanoparticle types. To determine the optimal weight ratio for an unknown particle type, it is useful to also carry out this protocol with magnetic nanoparticle stock suspensions resulting in w/w ratios of 0.25, 0.75, 1 and 1.25 or higher. 

The CVD method is usually used to produce a thin film material which is formed on a heated substrate. However, nanostructured particles of ceria and ceria-yttria have been synthesized by some arrangements of the apparatus. Figure 3.8 shows the schematic CVD reactors for synthesizing ceria-based nanoparticles. Two types of rector has been presented. The nanoparticles are collected either on a cooled quartz susceptor (A) that is in a furnace, or in a cold wall container outside the fiimace (B). The precursor cerium chloride set on the container is evaporated and... 

Fig. 11 Dynamic interfacial tension (y) measurements of a hexane-water interface during adsorption of nanoparticles to a pendant water drop in hexane (for ail particle types, concentration was 1.2 x 10-4 mmol/L). The gold moieties were modified using dodecanethiol (DDT) or octade-canethiol (ODT). NP homogeneous nanoparticles, JP Janus particles. Reprinted with permission from Langmuir [68], Copyright (2006) American Chemical Society...

Systems of two different particle types and sizes have led to a wealth of possible superlattices with stoichiometry dependent on the particle size ratio (79-84). Murray and coworkers (81-84) showed that in addition to size ratio a key experimental component is to charge tune the nanoparticles with either oleic acid or trioctyl-phosphine to yield superlattice stoichiometries of AB, AB2, AB3, AB4, AB5, ABe, and ABi3, a greater diversity than foimd in nature for micron-sized particles (see Fig. 3.13). This charge tuning is successful because at the nanoscale (not the microscale) all the interactions above can contribute with comparable weight. These, combined with substrate interactions and the inherent nonequilibrium nature of the evaporative process to create the superlattices, yields the diversity. 

There are a variety of different types of particle that can be synthesized using microfluidics and the exact fluidic format used defines the flow characteristics of the synthesis environment which needs to be carefully matched to the synthetic requirements of each particle type. Broadly speaking, the main particle types of interest include monodisperse microgels, metal nanoparticles and nanocrystals, core-shell particles, microemulsions, and microcapsules. Typically these particles should be homogeneous in size and are composed either of an organic polymer matrix or a metal or metal mixture at the micron or nanometer scale. In addition to these simple particle architectures, we may also consider more complex particles composed of multiple layers or components such as core-shell particles or using a central cavity to encapsulate small molecules, proteins, or other particles, and these are called microcapsules. 

Because of its inherent costs, spray drying is not always considered as a processing option for many conventional formulations. However, when a specialized particle type is required by the active ingredient or dosage form, spray drying can become a feasible alternative to more conventional manufacturing processes. Such particle types include microcapsules, controlled release particles, nanoparticles, and liposomes. The application of spray drying to pharmaceuticals has been extensively discussed in review articles (21,22). 

Nanocellulose can broadly be defined as a set of particles having at least one dimension in nanoscale obtained by different mechanical/chemical, or only chemical, or acid-hydrolysis methods. According to a survey of the literature, there is no standardized nomenclature for cellulose-based nanoparticles, while various terms have been used to describe a particular set of cellulose nanoparticles. Because of inconsistency in use of these terms, there are some particle types depending on source materials of cellulose and method of extraction. However, depending on their aspect ratio, nanocelluloses have already been characterized with different terms like microfibrillated cellulose (MFC-diameter 10-100 nm) [34], nanofibrillated cellulose (NFC-diameter 4-20 nm) [35], CNCs (CNCs-diameter 3-5 nm) [34, 36], tunicate CNCs (t-CNCs-diameter 20 nm) [34, 37], algae cellulose particles (AC-diameter 20 nm) [38,39], bacterial cellulose particles (BC-diameter 6-50 nm) [40, 41]. It can commonly be called "nanocellulose,"... 

The first SERS experiments were performed with electrochemically roughened electrodes and metal colloids, and many other types of suitable SERS substrates are known - e.g. metal island films, metal films over nanoparticles (see Fig. 4.58, below) or rough substrates, gratings, and sputter-deposited metal particles. 

In an effort to restrict the location of semiconductor nanoparticles in LB films and inhibit aggregation, the formation of CdS in LB films of calixarenes was investigated [195]. Limiting areas of 3.0 nm and 1.8 nm were obtained on 0.5 mM CdCli, compatible with the cross-sectional areas of the calixarenes. Y-type LB fdms were prepared at 25 mN m on glass, quartz, and silicon. The substrates had been made hydrophobic by treatment with a silane vapor. After H2S treatment overnight in sealed jars, UV absorbance spectra and XPS data were obtained. The absorption edge for the CdS particles formed in the calixarene LB films transferred at pH 5.5 was 3.3 eV as compared with 2.7 eV for films formed in cad-... 

Thus, previously described experiments had demonstrated the possibility of realization of single-electron junctions based on CdS nanoparticles. Nevertheless, because only one type of particle was tested, the question about the role of the material s properties for successful single-electron junction formation was still open. 

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