Forces of Interaction between DNA-Grafted Colloids: An Optical Tweezer Measurement

Kegler, K.; Salomo, M.; Kremer, Friedrich

doi:10.1103/physrevlett.98.058304

Cited by 82 publications

(89 citation statements)

References 40 publications

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“…Strong polyelectrolyte brushes that have so far been reported in the literature were predominantly made of a few different molecules: poly(styrene sulfonate) (PSS), 20,50−53 poly(vinyl methyl pyridinium) (PVP), 54 and double-stranded DNA. 55,56 When compared to these brushes, HA brushes reveal particular features.…”

Section: ■ Discussionmentioning

confidence: 99%

Films of End-Grafted Hyaluronan Are a Prototype of a Brush of a Strongly Charged, Semiflexible Polyelectrolyte with Intrinsic Excluded Volume

2012

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Hyaluronan (HA) is a naturally occurring linear, negatively charged polysaccharide that plays a vital role in the organization and function of pericellular coats and extracellular matrices in vertebrates, and that is becoming increasingly popular in biomedical applications. To gain insight into the physical phenomena that govern the mechanical behavior of HA assemblies, we have studied the response of films of end-grafted HA to compression over a large range of ionic strength. Compression forces were measured as a function of the absolute distance between a colloidal probe and the planar surface on which the HA film was constructed, using a combined atomic force microscopy and reflection interference contrast microscopy setup. The HA films were well-defined in the sense that they are made of chains with a narrow size distribution that are grafted at controlled density to a solid support. Detailed comparison of the experimental data with analytical expressions derived from polymer and polyelectrolyte brush theory reveals that films of end-grafted HA behave as strongly charged polyelectrolyte brushes. To quantitatively reproduce the experimental data, intrinsic excluded volume interactions and chain stiffness of the polymer backbone must be taken into account. At low ionic strength, chains become almost fully stretched. In our experimental system, several micrometer thick films are formed that reach a hydration of up to 99.98%, and the brush thickness decreases by more than 5-fold with increasing ionic strength. More generally, the study provides quantitative theoretical predictions for the film thickness and compressive response as a function of HA length, grafting density and ionic strength. ■ INTRODUCTIONThe polysaccharide hyaluronan (HA) is ubiquitous in the pericellular and extracellular space of vertebrates. It is also becoming increasingly popular in biomedical applications as surface coating 1 and in tissue engineering. 2,3 HA is a linear polymer of disaccharides, made of glucuronic acid and Nacetylglucosamine, that are linked via alternating β-1,4 and β-1,3 glycosidic bonds. Each disaccharide has a length of 1 nm 4 and carries one chargeable group in the form of a carboxylic acid. For polymeric HA, the pK a is approximately 3, 5 and HA is, hence, negatively charged above pH ≈ 3. In vivo, HA is expressed by HA synthases at the cell membrane and extruded into the extracellular space. These HA molecules have a molecular mass of typically a few million Daltons 6 or a contour length of several micrometers. Once produced, they can stay grafted to the synthases and/or bind to other HA receptors at the cell surface, such as CD44 7 and form so-called pericellular coats (PCCs), or they can be released into solution to serve other functions in the extracellular space. Numerous biological functions of PCCs 8−11 and extracellular assemblies of HA in general (e.g., in cartilage) have been related to their mechanical properties. To better understand how the mechanical properties of PCCs are connected to their ...

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Section: ■ Discussionmentioning

confidence: 99%

Films of End-Grafted Hyaluronan Are a Prototype of a Brush of a Strongly Charged, Semiflexible Polyelectrolyte with Intrinsic Excluded Volume

2012

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“…On the other hand, systems with non-trivial interactions can be constructed. This includes charged particles which interact over a range of a few diameters [22], polymer coated particles interacting via mushroom-like potentials [23] or polymer coils, which in a good solvent behave effectively like soft, Gaussian-profiled particles [24]. The systematic molecular dynamics simulations for various combinations of repulsions and attractions in the systems have also shown that unexpected effects can be encountered, e.g.…”

Section: Introductionmentioning

confidence: 99%

Analytical theory of effective interactions in binary colloidal systems of soft particles

Majka

Góra

2014

Phys. Rev. E

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While the density functional theory with integral equations techniques are very efficient tools in numerical analysis of complex fluids, an analytical insight into the phenomenon of effective interactions is still limited. In this paper we propose a theory of binary systems which results in a relatively simple analytical expression combining arbitrary microscopic potentials into the effective interaction. The derivation is based on translating many particle Hamiltonian including particle-depletant and depletant-depletant interactions into the occupation field language. Such transformation turns the partition function into multiple Gaussian integrals, regardless of what microscopic potentials are chosen. In result, we calculate the effective Hamiltonian and discuss when our formula is a dominant contribution to the effective interactions. Our theory allows us to analytically reproduce several important characteristics of systems under scrutiny. In particular, we analyze the effective attraction as a demixing factor in the binary systems of Gaussian particles, effective interactions in the binary mixtures of Yukawa particles and the system of particles consisting of both repulsive core and attractive/repulsive Yukawa interaction tail, for which we reproduce the 'attraction-through-repulsion' and 'repulsion-through-attraction' effects.

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“…The force F (D) and the surface-to-surface separation D between two identical, negatively charged DNA-grafted colloids is measured using optical tweezers in a identical set-up as used in Ref. [13].We employed colloidal particles with a hard core radius R c = 1100 nm, on which DNA-strands with various numbers of base pairs (bp) and grafting densities σ were chemically anchored. The brush has only a slight deviation from planarity, which allows us to relate also to known facts from planar PE-brushes in what follows.…”

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confidence: 99%

Polyelectrolyte-Compression Forces between Spherical DNA Brushes

et al. 2008

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Optical tweezers are employed to measure the forces of interaction within a single pair of DNAgrafted colloids in dependence of the molecular weight of the DNA-chains, and the concentration and valence of the surrounding ionic medium. The resulting forces are short-range and set in as the surface-to-surface distance between the colloidal cores reaches the value of the brush height. The measured force-distance dependence is analyzed by means of a theoretical treatment based on the compression of the chains on the surface of the opposite-lying colloid. Quantitative agreement with the experiment is obtained for all parameter combinations.PACS numbers: 82.35. Rs, 82.70.Dd, 87.80.Cc Surface treatment of colloidal particles and the ensuing manipulation and control of their interaction properties is a topic of high and lasting interest, on the grounds of both technological relevance and fundamental importance. On the first count, the main issue pertains to the fact that surface treatment is necessary to achieve colloidal stabilization by inducing thereby a repulsive force that acts against the ubiquitous dispersion attractions between the colloids. Charge stabilization and steric stabilization, the latter being caused by grafted polymer chains, are the two most common mechanisms, whereas grafting of polyelectrolyte (PE) chains on a colloid provides a natural combination of both and results to an electrosteric repulsion. On the second count, surface treatment by polymer grafting provides the possibility to tune the effective colloid interaction by 'dressing' the hard sphere potential with a soft tail, whose range, strength and overall functional form can be controlled by changing the properties of the polymer brush, e.g., its grafting density, height or charge. Systems interacting by a combination of a hard sphere potential and a subsequent short-range repulsion show a tremendous variety in their equilibrium [1,2,3,4] and dynamical [5,6,7] properties.Considerable work has been carried out in the study of the so-called osmotic PE-brushes [8, 9, 10], which result for high surface grafting densities and are characterized by the fact that they spherically condense the vast majority of the counterions released by the chains. These, in turn, bring about an entropic effective force between the brushes, which has been quantitatively analyzed for PE-brushes [11] and stars [12]. On the other hand, little is known for the opposite case of low surface grafting density, for which the theoretical considerations that lead to the interaction between osmotic brushes break down. In this Letter, we investigate by a combination of sensitive and accurate experiments and theoretical analysis the effective forces between spherical DNA brushes and establish a novel mechanism of interaction between those, which results from the mutual compression of PEchains of the colloids against the surface of each other. The quantitative characteristics of the resulting forces are vastly different from those between osmotic brushes.The experimental inves...

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Forces of Interaction between DNA-Grafted Colloids: An Optical Tweezer Measurement

Cited by 82 publications

References 40 publications

Films of End-Grafted Hyaluronan Are a Prototype of a Brush of a Strongly Charged, Semiflexible Polyelectrolyte with Intrinsic Excluded Volume

Films of End-Grafted Hyaluronan Are a Prototype of a Brush of a Strongly Charged, Semiflexible Polyelectrolyte with Intrinsic Excluded Volume

Analytical theory of effective interactions in binary colloidal systems of soft particles

Polyelectrolyte-Compression Forces between Spherical DNA Brushes

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