Nano Res 2012, 5:235–247.CrossRef 17. Hong SS, Cha JJ, Cui Y: One nanometer resolution electrical probe via atomic metal filament formation. Nano Lett 2011, 11:231–235.CrossRef Competing interests The authors declare that they have no competing interests. Authors’ contributions MT performed all the AFM measurements and wrote the manuscript. HF and SH developed the

technology behind the sample preparation and consequently prepared the samples. Corrections to the manuscript were also provided. SS, TG and MH put the basis of the entire project, guided the internal collaboration, and read and improved the manuscript. All authors read and approved the final manuscript.”
“Background There are a lot of types of nanoparticles and colloidal particles in groundwater [1]. SBI-0206965 mw Some of them are formed naturally, others are Selleck Ferrostatin-1 generated synthetically and put into the ground by humans. Not only is the reactivity of particles important, but also their migration properties are examined. For example, natural bentonite colloids are released as a consequence of bentonite disposal of radioactive wastes and could carry adsorbed radionuclides in groundwater through granite [2, 3]. PF01367338 Zero-valent iron nanoparticles are produced [4–6] and injected into the ground. Iron nanoparticles are able to migrate in groundwater through contaminated areas and remediate the polluted soils and water [7]. In the first case, the migration

possibility is unwelcome. In the second case, the better the migration, the more effective of the remediation. That is why a simulation

of the migration of nanoparticles might be desirable. To simulate the migration of nanoparticles, the coefficient of transport retardation of the nanoparticles is needed. The coefficient represents the possible reduction in the over rate of nanoparticle migration compared with nanoparticles with similar properties. The number of nanoparticles with similar properties changes over time due to aggregation and it influences the results of the migration experiments. A dynamic model of aggregation has to be included in the simulation programme of nanoparticle transport in flowing water. That is why mass transport coefficients are needed. The coefficients represent the frequency of nanoparticle collisions [8, 9]. A commonly used model for mass transport coefficients [10, 11] in describing aggregation is based on the collisions among nanoparticles caused by heat fluctuation, the velocity gradient of the water in which the nanoparticles are suspended and the different velocities of sedimentation of nanoparticles of varying size. This model does not include the decrease in the rate of aggregation due to repulsive electrostatic forces which occurs due to the electric double layer which builds up on nanoparticle surfaces [12]. Further, in the case of magnetic nanoparticles, the aggregation rate is rapidly increased due to the attractive magnetic forces between nanoparticles [4, 13–16].