BackgroundThe rapid growth of the nanotechnology industry and the wide application of various nanomaterials have raised concerns over their impact on the environment and human health. Yet little is known about the mechanism of cellular uptake and cytotoxicity of nanoparticles. An array of nanomaterials has recently been introduced into cancer research promising for remarkable improvements in diagnosis and treatment of the disease. Among them, quantum dots (QDs) distinguish themselves in offering many intrinsic photophysical properties that are desirable for targeted imaging and drug delivery.ResultsWe explored the kinetics and mechanism of cellular uptake of QDs with different surface coatings in two human mammary cells. Using fluorescence microscopy and laser scanning cytometry (LSC), we found that both MCF-7 and MCF-10A cells internalized large amount of QD655-COOH, but the percentage of endocytosing cells is slightly higher in MCF-7 cell line than in MCF-10A cell line. Live cell fluorescent imaging showed that QD cellular uptake increases with time over 40 h of incubation. Staining cells with dyes specific to various intracellular organelles indicated that QDs were localized in lysosomes. Transmission electron microscopy (TEM) images suggested a potential pathway for QD cellular uptake mechanism involving three major stages: endocytosis, sequestration in early endosomes, and translocation to later endosomes or lysosomes. No cytotoxicity was observed in cells incubated with 0.8 nM of QDs for a period of 72 h.ConclusionsThe findings presented here provide information on the mechanism of QD endocytosis that could be exploited to reduce non-specific targeting, thereby improving specific targeting of QDs in cancer diagnosis and treatment applications. These findings are also important in understanding the cytotoxicity of nanomaterials and in emphasizing the importance of strict environmental control of nanoparticles.

Immunomagnetic isolation and magnetophoresis in microfluidics have emerged as viable techniques for the separation, fractionation, and enrichment of rare cells. Here we present the development and characterization of a microfluidic system that incorporates an angled permanent magnet for the lateral magnetophoresis of superparamagnetic beads and labeled cell-bead complexes. A numerical model, based on the relevant transport processes, is developed as a design tool for the demonstration and prediction of magnetophoretic displacement. We employ a dimensionless magnetophoresis parameter to efficiently investigate the design space, gain insight into the physics of the system, and compare results across the vast spectrum of magnetophoretic microfluidic systems. The numerical model and theoretical analysis are experimentally validated by the lateral magnetophoretic deflection of superparamagnetic beads and magnetically labeled breast adenocarcinoma MCF-7 cells in a microfluidic device that incorporates a permanent magnet angled relative to the flow. Through the dimensionless magnetophoresis parameter, the transition between regimes of magnetophoretic action, from hydrodynamically dominated (magnetic deflection) to magnetically dominated (magnetic capture), is experimentally identified. This powerful tool and theoretical framework enables efficient device and experiment design of biologically relevant systems, taking into account their inherent variability and labeling distributions. This analysis identifies the necessary beads, magnet configuration (orientation), magnet type (permanent, ferromagnetic, electromagnet), flow rate, channel geometry, and buffer to achieve the desired level of magnetophoretic deflection or capture.

The rates and mechanism of coreactant electrogenerated chemiluminescence (ECL) from tris(2,2‘-bipyridyl)ruthenium(II) (Ru(bpy)3 2+) and the tertiary amines, tripropylamine (TPrA) and trimethylamine (TMeA), in aqueous solution were investigated. Transient (0.5 ms) potential steps were used with microelectrodes to investigate the emission time course under a variety of solution conditions. With amine concentrations that are low with respect to Ru(bpy)3 2+, the emission rises continually during the transient potential step and decays slowly after its termination. In contrast, the emission approaches a plateau during the potential step and is rapidly extinguished afterward with concentrations of Ru(bpy)3 2+ that are much lower than the amine concentration. At intermediate pH values, the emission intensity increases approximately linearly with pH. The emission after the potential step is unaffected by the rest potential. To simulate these temporal characteristics by finite difference methods, a mechanism employing 15 discrete chemical and electrochemical steps was employed, using literature-based thermodynamic values and electron-transfer rate constants evaluated from Marcus theory. The rate-limiting step was found to be the deprotonation of the amine radical cation. In addition, the simulations required a rate constant for the homogeneous oxidation of the tertiary amine by electrogenerated Ru(bpy)3 3+ value much below its Marcusian-calculated value to match the experimental data.

Microfluidic devices made from poly(dimethylsiloxane) (PDMS) are gas permeable and have been used to provide accurate on-chip oxygen regulation. However, pervaporation in PDMS devices can rapidly lead to dramatic changes in solution osmotic pressure. In the present study, we demonstrate a new method for on-chip oxygen control using pre-equilibrated aqueous solutions in gas-control channels to regulate the oxygen content in stagnant microfluidic test chambers. An off-chip gas exchanger is used to equilibrate each control solution prior to entering the chip. Using this strategy, problems due to pervaporation are considerably reduced. An integrated PDMS-based oxygen sensor allows accurate real-time measurements of the oxygen within the microfluidic chamber. The measurements were found to be consistent with predictions from finite-element modeling.