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Diffusion of nanoparticles probes the mesh formed by the biopolyelectrolytes

Diffusion of nanoparticles probes the mesh formed by the biopolyelectrolytes Marko Šoštar, Galja Pletikapić Ruđer Bošković Institute, Zagreb, Croatia Damir Aumiler, Tomislav Vuletić Institute of physics, Zagreb, Croatia Single celled organisms produce extracellular matrix (ECM) as a vehicle towards collective behavior in formation of biofilms and colonies [1]. This matrix may facilitate sessile adhesion, protect against drying, invasion of other organisms and harmful particles and substances, stabilize the habitat, form chemical microenvironments. The main component are polysaccharides, in most cases anionic (polyelectrolytes) which form networks that may be regarded as physical gels. Gels are a unique form of molecular organization in which the polymer chains that form their networks are interconnected by chemical or physical cross-links, keeping these chains in a statistically stable neighborhood. Physical networks stabilized by tangles and hydrophobic, or ionic linkages, can readily disperse. With this characteristic in mind, as a model system for ECM we can take the mesh formed by semirigid polyelectrolytes deoxyribonucleic acid (DNA) and hyaluronic acid (HA, a polysaccharide) in the semidilute regime, across a broad concentration range (10−3 − 102 g/L). Salt-free polyelectrolytes are distinct from uncharged polymers as they presumably form a rather rigid, isotropic mesh, quite gel-like at higher concentrations. The polyelectrolyte characteristic mesh size is known as de Gennes correlation length ξ . We directly probed the mesh formed by DNA and HA, by employing fluorescence correlation spectroscopy (FCS) to measure the diffusion coefficient of fluorescently labeled DNA fragments (40 nm long, 2.5 nm diameter) added in trace amounts [2]. For the salt-free solutions we found that the DNA or HA mesh size has to be 2−3 times larger than the fragments for them to start to diffuse freely (as if in the dilute solution). For a tighter mesh (concentrations 0.1−1 g/L), the fragment diffusion coefficient is only half the free diffusion value. Conversely, fragments show the free diffusion coefficient as if there is no mesh in DNA or HA in 10 mM buffer. Currently we work on extending this study by FCS measurements of DNA probe fragments diffusion in a natural polymer network produced by marine diatoms [3]. We propose that FCS should be a method of choice when probing any such mesh with other nanoparticles, however, the labeling of e.g. graphene flakes or carbon nanotubes with appropriate fluorescent molecules is a prerequisite. [1] M. Trejo, C. Douarche, V. Bailleux, C. Poulard, S. Mariot, C. Regeard, and E. Raspaud, Elasticity and wrinkled morphology of Bacillus subtilis pellicles PNAS, 2013, 110, 2011–2016. [2] K. Salamon, D. Aumiler, G. Pabst and T. Vuletić, Probing the Mesh Formed by the Semirigid Polyelectrolytes Macromolecules 2013, 46, 1107−1118. [3] Svetličić, V. ; Žutić, V. ; Mišić Radić, T. ; Pletikapić, G. ; Hozić Zimmerman, A. ; Urbani, R. Polymer networks produced by marine diatoms in the northern Adriatic Sea. Mar. Drugs 2011, 9, 666–679.

FCS; marine gel; polyelectrolytes; diffusion

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