Surface charge plays an important role in determining the interactions of nanoparticles with biological components. Substantial studies have demonstrated that surface charge affects the fate of nanoparticles after intravenous administration; however, few studies have investigated the effect of surface charge on the bioavailability and absorption of nanoparticles after oral administration. In this study, polymeric nanoparticles with a similar particle size and surface polyethylene glycol (PEG) density, but with varying surface charges (positive, negative and neutral), were developed to study the effect of surface charge on the oral absorption of polymeric nanoparticles. The nanoparticles were constructed from polyethylene glycol-block-polylactic acid (PEG-PLA) with the incorporation of lipid components with different charges. Our results suggested that the positive surface charge facilitated the cellular uptake and transport of nanoparticles through both Caco-2 cells in vitro and small intestinal epithelial cells in vivo. The positively charged nanoparticles showed a favorable distribution in the small intestine, and significantly improved the oral bioavailability. This study presents valuable information towards the design of nanoparticles for improved oral drug delivery.

Miniaturized bioanalytical systems are increasingly being used in the field of biochemical research. Immobilized enzyme microbioreactors in capillary electrophoresis (CE) have been constructed and used to fulfill the increasing demands for miniaturized bioanalytical systems. This manipulation permits low sample consumption, reduced costs, short analysis times and efficient analyses. This review provides an overview of the distinct characteristics of immobilized microbioreactors in CE. After an introduction on miniaturized microreactors, the various methods of enzyme immobilization will be discussed. The emphasis will be on two common constructions of microreactors in CE, i.e. CE-coupled microreactors, and microreactors directly integrated into the CE capillary. Such microbioreactors offer straightforward automation of reaction steps followed by separation in the same capillary.