Multiple-particle tracking

As gene carriers are internalized by endocytosis, the motion characteristics inside the cell resembles the movement of the endosomal compartments within the cell and the formed vesicles are transported along the microtubule network [38]. Suh et al. [41] quantified the transport of individual internalized polyplexes by multiple-particle tracking and showed that the intracellular transport characteristics of polyplexes depend on spatial location and time posttransfection. Within 30 min, polyplexes accumulated around the nucleus. An average of the transport modes over a 22.5 h period after transfection showed that the largest fraction of polyplexes with active transport was found in the peripheral region of the cells whereas polyplexes close to the nucleus were largely diffusive and subdiffusive. Disruption of the microtubule network by nocodazole completely inhibits active transport and also the perinuclear accumulation of polyplexes [37, 40, 47]. 

Suh J, Wirtz D, Hanes J (2004) Real-time intracellular transport of gene nanocarriers studied by multiple particle tracking. Biotechnol Prog 20 598-602... 

The need to overcome intracellular barriers may require improved methods of determining rate-limiting steps for specific gene carriers, which will lead to the rational design of new carriers. To this end, our lab uses multiple-particle tracking (MPT) to investigate quantitatively the motion of nanometersized DNA delivery vehicles [170],... 

Steps taken to understand the intracellular barriers to gene delivery have led to the rational modification and improvement of carriers. Quantitative methods, such as multiple-particle tracking, to assess to the intracellular transport of gene carriers promise to add valuable insight that may ultimately lead to nonviral carriers rivaling the efficiencies seen in viral systems. 

Apgar J, Tseng Y, Fedorov E, Herwig MB, Almo SC, Wirtz D. Multiple-particle tracking measurements of heterogeneities in solutions of actin filaments and actin bundles. Biophys J 2000, 79, 1095-1106. 

Multiple-Particle Tracking (MPT) Measurements of Heterogeneities in Acrylic Thickener Solutions... 

Keywords Acrylic thickeners Microheterogeneity Microrheology Multiple-particle tracking... 

Y. Tseng and D. Wirtz. Mechanics and multiple-particle tracking microheterogeneity of a-actinin-cross-linked actin filament networks, Biophys. J., 81 (2001), 1643-1656. 

M. T. Valentine, Z. E. Perlman, M. L. Gardel, et al. Colloid surface chemistry critically affects multiple particle tracking measurements of biomaterials. Biophys. J., 86 (2004), 4004 014. 

J. Xu, Y. Tseng, C. J. Carriere, and D. Wirtz. Microheterogeneity and microrheology of wheat gliadin suspensions studied by multiple-particle tracking. Biomacromolecules, 3 (2002), 92-99. 

The particle tracking-based advective control model described in this chapter is capable of solving two- and three-dimensional plume capture problems with multiple candidate wells and multiple particles in confined and unconfined aquifers. The formulation provides a direct approach to solving plume control problems and uses both forward and reverse particle tracking to exploit numerical characteristics of the two reference frames. 

Features of PEPT of particular benefit to engineering studies include the fact that the actual particles of interest may be used as tracers, rather than dissimilar materials of unknown behaviour, and that y-rays are sufficiently penetrating that location is unimpaired by the presence of metal walls, for example. In recent developments, the minimum size of particles which can be tracked has been reduced to approximately 60 pm. It is now possible to track multiple particles, to determine particle rotation and to track motion within real industrial equipment by use of a mobile modular positron camera. These developments are described later. 

Fig. 1 0.11 Predicted particle tracks through multiple revolutions of a Triflat tool from a two-dimensional computational fluid dynamics model. The cumulative number of revolutions (n) in each case is indicated. Adapted from Ref 47...

Turning now to alpha radiation, the track density is such that almost any overlap with a macromolecule results in multiple hits. For 2-m.e.v. alpha particles, a dose of r rads requires a flux of only 4 X 104 r particles per sq. cm., and with a track radius a = 15A., the total area covered is only 2.8 X 10"9 r per sq. cm. For 50% of target molecules to be hit at the doses envisaged each must have a larger area. 

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