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Inorganic nanoparticles such as magnetic nanoparticles, fluorescent quantum dots, and plasmonic nanoparticles can be used as building blocks for designing multifunctional systems based on polymeric capsules. The properties of the inorganic nanoparticles hereby are harnessed to provide additional functionality to the polymer capsules. Biological applications towards in vitro sensing and delivery are discussed. Examples will be given in which magnetic nanoparticles are used to direct capsules with magnetic field gradients, colloidal quantum dots are used to identify capsules via the formation of optical barcodes, and gold nanoparticles are used as light-controlled heat-sources for opening capsules and releasing macromolecules from their cavity upon optical excitation. This demonstrates that combination of inorganic nanoparticles and organic/polymeric molecules as carrier matrices allow for tailoring multifunctional hybrid particles for practical applications.

Besides the typical short-lived fluorescence with decay times in the nanosecond range, colloidal II/VI semiconductor nanoparticles dispersed in buffer also possess a long-lived fluorescence component with decay times in the microsecond range. Here, the signal intensity of the long-lived luminescence at microsecond range is shown to increase 1,000-fold for CdTe nanoparticles in PBS buffer. This long-lived fluorescence can be conveniently employed for time-gated fluorescence detection, which allows for improved signal-to-noise ratio and thus the use of low concentrations of nanoparticles. The detection principle is demonstrated with a time-resolved fluorescence immunoassay for the detection of C-reactive protein (CRP) using CdSe-ZnS nanoparticles and green light excitation. [ABSTRACT FROM AUTHOR]

In the first paper of this series we have shown for hydrophilic coated Au nanoparticles that capillary electrophoresis in combination with Taylor dispersion analysis in fused silica capillaries with an inner diameter of 75 μm allows for the unbiased precise determination of the number-weighted mean hydrodynamic diameter, the zeta potential and the effective charge number, although mobility corrected double layer polarization has to be taken into account. In this second paper we investigate whether the modified approximate analytic expression developed by Ohshima (2001) permits the calculation of calibration lines and the concomitant conversion of electropherograms into number-weighted particle radius distributions. We show that with the method developed size distributions are obtained which are independent of the measurement conditions. These size distributions are much narrower than those obtained via dynamic light scattering and data evaluation by the CONTIN algorithm. Capillary electrophoresis together with the proposed data evaluation method reveals that the analyzed nanoparticle populations have very narrow size distributions with a width of 2–4 nm. The hydrodynamic radius distributions of the coated NPs are only slightly broader than the solid particle radius distribution of the Au-NP cores. The presence of monomodal/bimodal size distributions is confirmed by asymmetric flow field-flow fractionation. [ABSTRACT FROM AUTHOR]

Taking gold nanoparticles with different hydrophilic coatings as an example, it is investigated whether capillary electrophoresis in combination with Taylor dispersion analysis allows for the precise determination of mean electrophoretic mobilities, electrophoretic mobility distributions, and zeta potentials in a matrix of exactly known composition and the calibration-free determination of number-weighted mean hydrodynamic radii. Our experimental data confirm that the calculation of the zeta potential for colloidal nanoparticles with ζ > 25 mV requires to take the relaxation effect into account. Because of the requirement to avoid particle–wall interactions, a solution of disodiumtetraborate decahydrate (borax) in deionized water had been selected as suitable electrolyte. Measurements of the electrophoretic mobility at different ionic strength and application of the analytic approximation developed by Ohshima show that in the present case of a buffered solution with a weak electrolyte co-ion and a strong electrolyte counterion, the effective ionic drag coefficient should be approximated with the ionic drag coefficient of the counterion. The obtained results are in good agreement with theoretical expectations regarding the dependence of the zeta potential and the electrokinetic surface charge density on the ionic strength. We also show that Taylor dispersion analysis (besides estimation of the number-weighted mean hydrodynamic radius) provides additional information on the type and width of the number-weighted particle distribution. [ABSTRACT FROM AUTHOR]