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Quantum dot (QD) emits light of characteristic wavelength which depends on the size of the QD particles, and thus the quality control of QD requires accurate determination of its size distribution. Field-flow fractionation (FFF) is a separation technique that is well suited for the characterization of colloidal particles. In this study, CdS-QD particles were synthesized by a simple one-step γ-ray irradiation. Then asymmetrical flow FFF (AsFlFFF) and sedimentation FFF (SdFFF) were tested as tools for characterization of the particles. The single crystallite size of CdS-QD was measured to be about 4 nm by X-ray diffraction (XRD), UV-VIS absorption spectroscopy, and transmission electron microscopy (TEM). TEM images indicate that the particles were agglomerated to form larger secondary particles (∼ 110 nm). Effects of the various experimental parameters of FFF including the type of dispersing agent, the ionic strength of the carrier liquid, and strength of external field were investigated. It was found that, among the dispersing agents tested, a mixture of anionic and nonionic surfactants tends to give better elution of CdS particles than anionic or nonionic surfactants. Results suggest that FFF can provide some advantages over dynamic light scattering (DLS) or TEM for size characterization of CdS particles, and with a proper optimization, FFF (AsFlFFF or SdFFF) could become a useful tool for stability study as well as size analysis of nanoparticles such as the CdS particles synthesized in this study. [ABSTRACT FROM AUTHOR]

An Acaligense sp.-immobilized biosensor was fabricated based on QD-MWNT composites as an electron transfer mediator and a microbe immobilization support by a one-step radiation reaction and used for sensing phenolic compounds in commercial red wines. First, a quantum dot-modified multi-wall carbon nanotube (QD-MWNT) composite was prepared in the presence of MWNT by a one-step radiation reaction in an aqueous solution at room temperature. The successful preparation of the QD-MWNT composite was confirmed by XPS, TEM, and elemental analysis. Second, the microbial biosensor was fabricated by immobilization of Acaligense sp. on the surface of the composite thin film of a glassy carbon (GC) electrode, which was prepared by a hand casting method with a mixture of the previously obtained composite and Nafion solution. The sensing ranges of the microbial biosensor based on CdS-MWNT and Cu2S-MWNT supports were 0.5-5.0 mM and 0.7-10 mM for phenol in a phosphate buffer solution, respectively. Total concentration of phenolic compounds contained in commercial red wines was also determined using the prepared microbial immobilized biosensor. [ABSTRACT FROM AUTHOR]

Polyamidoamine (PAMAM) dendrimers have an amine surface and an ethylenediamine core and are of great interest in various applications such as in drug delivery. Physiochemical properties of PAMAM dendrimers vary with pH. At neutral to basic pH, PAMAM dendrimers are either weakly charged or uncharged and tend to adsorb on to the neutral packing material, making chromatographic separation of the dendrimers difficult. Asymmetrical flow field-flow fractionation (AsFlFFF) was tested as an alternative to the chromatographic techniques for separation of the PAMAM dendrimers. AsFlFFF provided generation-based separation of the dendrimers even at neutral and basic pH. The elution time increased gradually as the generation number (and thus the size) increased. Separation of impurities such as generational or missing-arm impurities and aggregates from the main population was also achieved. Electrostatic and hydrophobic interactions (e.g., repulsive elecrostatic interaction among the dendrimer molecules or attractive hydrophobic interaction between the dendrimer molecules and the membrane) may result in an inaccurate size measurement. Careful optimization of experimental conditions such as the flow rate, pH, and the salt concentration may be required to minimize the interactions with the membrane. AsFlFFF was also tested for a study on the interaction between the PAMAM dendrimers and proteins. AsFlFFF was able to show the growth in the size of bovine serum albumin (BSA) when BSA is mixed with increasing amounts of PAMAM dendrimers. Results suggest that, with proper optimization, AsFlFFF could become a useful tool for separation and characterization of large charged molecules such as PAMAM dendrimers. [ABSTRACT FROM AUTHOR]