Interfacial microrheology: Particle tracking and related techniques

Ortega, Francisco; Ritacco, Hernán; Rubio, Ramón G.

doi:10.1016/j.cocis.2010.03.001

Cited by 108 publications

(89 citation statements)

References 68 publications

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“…21 The method is well established to study quiescent 22 and driven 23 bulk systems but it is still in its infancy to probe interfacial phenomena. 24 In what follows we monitor the motion of fluorescent tracers (silica r z 400 nm) at a water/oil interface to investigate the irreversible adsorption 25,26 of anisotropic, unlabelled b-lactoglobulin amyloid fibrils. Structural changes in the interfacial, self-assembled nanoparticles monolayer are revealed by detecting topological variations in the probe particle traces.…”

Section: Resultsmentioning

confidence: 99%

Unravelling adsorption and alignment of amyloid fibrils at interfaces by probe particle tracking

2011

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We report the first direct, non-invasive experimental evidence of a 2D isotropic-nematic transition for highly anisotropic nanoparticles at liquid-liquid interfaces by using passive fluorescent particle tracking. In order to illustrate the potential of this approach on systems of high real practical and biological relevance, we select as a model anisotropic nanoparticles b-lactoglobulin amyloid fibrils of varying aspect ratios. Upon nanoparticle adsorption at the interface, we follow, in real time and as a function of fibril length and bulk concentration, the development of a 2D nematic phase by studying the anisotropy in probe particle traces. We furthermore demonstrate the long-range nature of the nematic phase by calculating order parameters for the traces as high as 0.8 over 10 2 to 10 3 mm 2 areas. The presented route is independent of the system investigated, and thus these findings open a new, general strategy for the experimental assessment of 2D structural changes at anisotropic fluid-fluid interfaces.

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Section: Resultsmentioning

confidence: 99%

Unravelling adsorption and alignment of amyloid fibrils at interfaces by probe particle tracking

2011

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“…We believe that this non-contact approach puts interfacial and membrane microrheology on a stronger footing and opens up new possibilities for the quantitative study of particular fragile and even heterogeneous monolayers. Figure 4.3 shows there is a significant discrepancy between the monolayer modulus obtained by macroscopic methods and by particle-tracking microrheology [81]. This discrepancy appears to be quite common, appearing in a variety of surfactant systems.…”

Section: Microrheology Of Membranesmentioning

confidence: 91%

“…In some regions as much as four orders of magnitude separate the two measurements, but the general trend in the moduli appears to be qualitatively similar. Adapted from Ortega et al [81] with permission Fig. 4.4 Schematic of particle-tracking microrheology and potential problems with the implementation.…”

Section: The Case Of the Missing Modulusmentioning

confidence: 98%

Membrane Rheology

Evans¹,

Levine²

2014

Complex Fluids in Biological Systems

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Surfactant monolayers and lipid bilayers are intrinsically two-dimensional structures with viscoelastic mechanical properties. Monolayers display a plethora of complex broken symmetry phases, each with its own rheological signature, while bilayers are of fundamental biological importance in forming the cell membrane and the principal internal partitions of the cell. Understanding the low-energy excitations and mechanical response of these materials is thus an important probe of novel two-dimensional phases and essential to biomechanics at the cellular level, cell recognition, and transport across membranes; as such, a number of macroscopic and microscopic techniques have been developed to explore the rheological properties of monolayers and membranes. In this chapter we review the fundamental physics and rheology of molecularly thin membranes, paying particular attention to the fact that these systems are necessarily bounded on one or both sides by an aqueous fluid. We develop the basic theory of both the in-and out-of-plane viscoelastic response of membranes and monolayers and apply this theory to the study of particle transport at the surface. Such transport measurements form the basis of typical rheological experiments. We also report on more recent investigations regarding the role of nontrivial membrane geometry on particle transport and examine a novel approach to monolayer and membrane microrheology using the thermal fluctuations of particles submerged beneath the membrane. We conclude with a discussion of open questions in the field and some speculations on future research directions. Overview of Membranes and Langmuir MonolayersThere is a class of molecules that, when introduced to water, spontaneously assemble at the air/water interface into a layer only one molecule thick. This nanoscale film is termed a Langmuir monolayer and its dynamics or rheology is the focus of the present chapter. While the ability to self-assemble into nanometerthick monolayers sounds like a dispatch from the frontiers of modern nanoscience, these systems are ubiquitous in nature and their study ancient in origin. In fact, such quotidian materials as olive oil and soap form these remarkable nanoscale structures. The historical record is rife with observations providing hints about these systems. Pliny the Elder remarked on the effect of oil on a body of water in the first century of the common era [1]:... all sea water is made smooth by oil, and so divers sprinkle oil on their face because it calms the rough element and carries light down with them.He was noting what was a common practice among divers in the Mediterranean who, by releasing a small quantity of oil that goes to the surface of the water above them and forms a thin film, flattened the waves and allowed for the better penetration of light into the depths. The spreading of oil on water was noted repeatedly over the next 2,000 years by others including Ben Franklin, who observed it from shipboard on a trip to England to complain about taxes (on behalf of the...

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“…An interesting option of this idea has been used for the development of particle tracking techniques. At present very large unexplained discrepancies still exist between the measured quantities obtained with this method and other ones [36]. Direct measuring techniques determine the displacement or torque of a measuring probe located within the interface.…”

Section: Such Layers Can Be Formed By Adsorption Of Soluble Interfacimentioning

confidence: 97%