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Over the last decade, considerable effort has been put in the implementation of RNA interference (RNAi) as a treatment for various disorders. As RNAi occurs in the cytoplasm of cells, it is imperative that RNAi mediators such as small interfering RNA (siRNA) cross several extracellular and intracellular barriers to reach this site of action. Among the extensive range of proposed delivery systems for siRNA, matrix systems possess interesting properties to promote the delivery of siRNA to a target tissue. In this review, a number of recently developed matrix and hybrid systems for siRNA delivery are discussed.

Single-particle tracking (SPT) microscopy is increasingly used to characterize nanoparticulate systems. We introduce a concept for estimation of particle number concentration in Brownian particle dispersions using SPT based on a model for the trajectory length distribution of particles to estimate the detection region volume. The resulting method is independent of precalibration reference measurements, and robust with respect to image processing settings. Experimentally estimated concentrations of different dilutions of 0.19-and 0.52-μm polymer nanospheres are in excellent agreement with estimates computed from the concentrations of the stock solutions.

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