New Plastic Microparticles and Nanoparticles for Fluorescent Sensing and Encoding.

We report on the progress that has been made in the area of luminescence sensing and encoding by making use of microparticles and nanoparticles prepared from plastic materials. These are quite different from particles built up from metal sulfides (such as the so-called quantum dots, "Q-dots"; see Michalet et al., Science 307:538, 2005), other semiconductor materials, metal nanoparticles (mainly gold) (see DL Feldheim, CA Foss (eds) Metal Nanoparticles: Synthesis, Characterization, and Applications, p 338, Marcel Dekker, 2002), or glass and its modifications including certain sol-gels. Plastic nanoparticles may contain magnetic beads in order to facilitate separation from the sample solution. All the particles described here are doped with fluorescent dyes, which is in contrast to particles where the material itself displays intrinsic luminescence. Unlike the case of Q-dots, the color of plastic beads can be varied to a wide extent irrespective of their size, as can be the decay times and even anisotropy. This, in fact, is a most attractive feature of such beads and makes them superior in many cases despite the undisputed utility of other types of particles in certain fields. The area of beads was almost exclusively occupied until 10 years ago by polystyrene beads (also referred to as latex beads) 0.1-5 μm in diameter. They are widely used in bioassays and flow cytometry because they can be manufactured with good reproducibility (usually by emulsion polymerization) and because they are rather inert. Other applications include agglutination tests, particle capture ELISAs (e.g., Abbott's IMx and AxSym), solid-phase assays (often used for pregnancy testing), scintillation proximity assays, luminescent oxygen channeling immunoassay (LOCI), and bead-FRET assays. Nanoparticles have been used for labeling purposes, particularly in the context of protein arrays and DNA arrays. In recent years, beads have been fluorescently dyed for purposes of encoding, for example in combination with optical fiber arrays and in microwells, and in methods for homogeneous multiplexed high-throughput screening. The analytical information may be the color of the fluorescence, its intensity (or—even better—the ratio of two intensities), decay time, anisotropy, or combinations thereof. In the first section we will describe dyes for doping plastic particles. The second section will report on chemical sensing with addressable micro- and nanospheres, and the third on the use of dyed microparticles in sensing pH values. We will also report on luminescence lifetime encoded microbeads as carriers for multiplexed bioassays (Sect. 4), the use of dyed polymer microparticles in simultaneous sensing of oxygen and temperature (Sect. 5), and on nanobead labels for homogeneous protein assays and protein arrays (Sect. 6). [ABSTRACT FROM AUTHOR]