Polymeric beads

III. PREPARATION OF ORGANIC POLYMERIC BEADS BY CONVENTIONAL SUSPENSION POLYMERIZATION... 

VI. APPLICATION OF POLYMERIC BEADS AS SIZE EXCLUSION CHROMATOGRAPHY SUPPORTS... 

Whereas for organic SEC column technology a particular type of bead (PS/ DVB) is used almost universally, in the field of aqueous SEC there have been a variety of approaches to derive polymeric beads suitable for the application. For this reason there is more secrecy about the chemical composition of the packing materials and columns produced by different manufacturers. 

AmberlysH BD20 Amber, spherical polymeric beads of 750 pm... 

Coleman, P.L., Walker, M.M., Milhrath, D.S., Stauffer, D.M., Rasmussen, J.K., Krepski, L.R., and Heilmann, S.M. (1990) Immobilization of Protein A at high density on azlactone-functional polymeric beads and their use in affinity chromatography./. Chromatogr. 512, 345-363. 

Abstract Dye-doped polymeric micro- and nanobeads represent smart analytical tools that have become very popular recently. They enable noninvasive contactless sensing and imaging of various analytical parameters on a nanoscale and are also widely employed in composite sensing materials, in suspension arrays, and as labels. This contribution gives an overview of materials and techniques used for preparation of dye-doped polymeric beads. It also provides examples of bead materials and their applications for optical sensing and imaging. 

Selected Examples of Dye-Doped Polymeric Bead Materials. 206... 

Be nontoxic. Low cytotoxicity is desirable but not essential for the choice of dyes. Evidently, cytotoxicity is greatly reduced upon immobilization of dyes into polymeric beads. However, even individual dye molecules that leach out of the beads may undesirably affect biological systems. This also refers to other lumino-phores such as quantum dots which are known to be highly toxic. 

Fig. 2 Chemical structures and typical spectral properties of the common fluorophores that can be used for staining of the polymeric beads...

Micro- and nanobeads with magnetic properties have recently become popular since these tools can be manipulated, e.g., collected in the region of interest. Magnetite nanoparticles are introduced in order to render the polymeric beads magnetic. Preparation and application of magnetic beads will be discussed in more detail in Sect 5.5. 

Polymeric beads obtained via emulsion polymerization, precipitation, etc. can be stained with dyes providing that both have functional groups available [7]. Covalent coupling is mostly preferred but the attachment based on strong electrostatic interactions is also feasible. This method is mostly used to design pH- and ion-sensitive micro- and nanobeads. The dynamic response of such systems can be... 

Precipitation is a rather widespread method of manufacturing polymeric beads [13,14] but it has only been sparsely used for the preparation of dyed beads [15,16], However, this versatile method is very promising due to its simplicity. It was recently... 

Precipitation was found to be a very useful method for preparation of nanobeads with magnetic properties [17] since not only indicators but also small lipophilic magnetite nanobeads (having diameter of a few nanometers) can be incorporated inside the polymeric beads. Such multifunctional magnetic beads can be guided to the region of interest, be collected and manipulated there. 

Dye-doped polymeric beads are commonly employed in different formats (Fig. 5), namely as water-dispersible nanosensors, labels and in composite materials (DLR-referenced and multianalyte sensors, sensor arrays, magnetic materials, etc.). The sensing properties of the dye-doped beads are of little or no relevance in some more specific materials, e.g., the beads intended for photodynamic therapy (PDT). The different formats and applications of the beads will be discussed in more detail in the following section, and the relative examples of sensing materials will be given. 

Similarly to dyes, some fluorescent proteins can be incorporated into polymeric beads to be used as an alternative for ion sensing. For example, a reporter protein (composed of a phosphate-binding protein, a FRET donor (cyan fluorescent protein) and a FRET acceptor (yellow fluorescent protein)) was incorporated into polyacrylamide nanobeads by Sun et al. [46]. FRET was inhibited upon binding of phosphate. Kopelman and co-workers [47] used a similar approach to design a nanosensor for copper ions. They have found that fluorescence of red fluorescent protein DsRed (commonly used as a label) is reversibly quenched by Cu2+ and Cu+. Both DsRed and Alexa Fluor 488 (used as a reference) were entrapped into polyacrylamide nanobeads. Typically, up to 2 ppb of copper ions can be reliably measured. It should be mentioned, that in contrast to much more robust dyes, mild conditions upon polymerization and purification are very important for immobilization of the biomolecule to avoid degradation. 

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