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Related Concept Videos

Diffusion01:21

Diffusion

Diffusion is a type of passive transport. In passive transport, a substance tends to move from an area of high concentration to an area of low concentration until the concentration is equal across the space. For example, take the diffusion of substances through the air. When someone opens a perfume bottle in a room filled with people, the perfume is at its highest concentration in the bottle and is at its lowest at the edges of the room. The perfume vapor will diffuse, or spread away, from the...
Diffusion01:12

Diffusion

Diffusion is the passive movement of substances down their concentration gradients—requiring no expenditure of cellular energy. Substances, such as molecules or ions, diffuse from an area of high concentration to an area of low concentration in the cytosol or across membranes. Eventually, the concentration will even out, with the substance moving randomly but causing no net change in concentration. Such a state is called dynamic equilibrium, which is essential for maintaining overall...
Passive Diffusion: Overview and Kinetics01:17

Passive Diffusion: Overview and Kinetics

Passive diffusion is a critical process that allows small lipophilic drugs to cross the cell membrane along a concentration gradient. This mechanism's efficiency depends on four primary factors: the membrane's surface area, the drug's lipid-water partition coefficient, the concentration gradient, and the membrane's thickness.
When administered orally, drugs establish a substantial concentration gradient between the gastrointestinal (GI) lumen and the bloodstream, expediting their diffusion into...
Protein Diffusion in the Membrane01:24

Protein Diffusion in the Membrane

Proteins show rotational as well as lateral diffusion across the membrane. The lateral diffusion of proteins was confirmed through the cell fusion experiment where mouse and human cells were fused, resulting in hybrid cells. When the human and mouse cells fused, the specific membrane proteins on human and mouse cells were marked with the red and green-fluorescent markers, respectively. Initially, the red and green fluorescence was located on the respective hemisphere of the cell. As time...
Facilitated Diffusion01:16

Facilitated Diffusion

The plasma membrane, a critical structure in cellular biology, houses an array of transporters, or carrier proteins, interspersed within its lipid bilayer. These proteins play a crucial role in solute transport through facilitated diffusion, a form of passive diffusion that uses transporters to move the molecules across the membrane.
In this process, substrates such as organic compounds and ions interact with a transporter on one side, triggering conformational changes in proteins that enable...
Facilitated Transport01:19

Facilitated Transport

The chemical and physical properties of plasma membranes cause them to be selectively permeable. Since plasma membranes have both hydrophobic and hydrophilic regions, substances need to be able to transverse both regions. The hydrophobic area of membranes repels substances such as charged ions. Therefore, such substances need special membrane proteins to cross a membrane successfully. In  facilitated transport, also known as facilitated diffusion, molecules and ions travel across a membrane via...

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Generating Controlled, Dynamic Chemical Landscapes to Study Microbial Behavior
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Enhanced diffusion due to active swimmers at a solid surface.

Gastón Miño1, Thomas E Mallouk, Thierry Darnige

  • 1PMMH, ESPCI, CNRS (UMR 7636) and Université Paris 6 and Paris 7, Paris, France.

Physical Review Letters
|March 17, 2011
PubMed
Summary
This summary is machine-generated.

Active swimmers like E. coli and Au-Pt rods enhance passive tracer movement near surfaces. Tracer diffusivity increases linearly with fluid activity, explained by swimmer-tracer interactions.

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Area of Science:

  • Soft Matter Physics
  • Active Matter Physics
  • Biophysics

Background:

  • Active swimmers, such as bacteria and synthetic micro-robots, exhibit complex motion near interfaces.
  • Understanding the interplay between active swimmers and passive tracers is crucial for microfluidics and biological systems.

Purpose of the Study:

  • To investigate the motion of active swimmers (E. coli and Au-Pt rods) near a solid surface.
  • To quantify the effect of active swimmer activity on the diffusion of passive tracers.
  • To establish a relationship between fluid activity and tracer diffusivity.

Main Methods:

  • Experimental observation of wild-type E. coli and self-propelled gold-platinum rods near a solid surface.
  • Classification of swimmer trajectories into ballistic (active) and random-like behaviors.
  • Measurement of passive tracer diffusivity in the presence of active swimmers.

Main Results:

  • Two distinct types of motion were identified for active swimmers at the surface.
  • Tracer diffusivity was found to be enhanced compared to standard Brownian motion.
  • Tracer diffusivity showed a linear dependence on fluid activity (fraction of active swimmers × mean velocity).

Conclusions:

  • Active swimmers significantly influence the dynamics of passive tracers in their vicinity.
  • The observed enhancement in tracer diffusivity can be attributed to direct interactions between swimmers and tracers.
  • This study provides a quantitative link between active fluid properties and enhanced diffusion.