engleski

Amperometric adhesion signals of vesicels, cells and droplets

The signifficance of adhesion phenomema in single particle/electrode interaction became apparent for more than two decades since the discovery of adhesion signals of vesicles in seawater using a dropping mercury electrode [1]. Electrochemical adhesion imaging presents unique approach for in situ characterization of fragile structures in marine systems [2] and in biological fluids [3]. By potential control of the electrode surface charge and interfacial tension, adhesion forces can be fine-tuned in studying interplay of complex processes involved in fluid microparticles/electrode interaction. During their attachment and spreading at the electrode, individual vesicles, cells and microdroplets displace the double-layer charge from the inner Helmholz plane, and the transient flow of compensating current can be recorded as well-defined adhesion signal. Liposomes present classical model in studying physical mechanism of cell adhesion [4]. Incidents and shape of adhesion signals recorded in liposome suspensions in PBS reflect their polydispersity, surface charge density and properties of phospholipid head group. Potential range of adhesion and the shape of adhesion signals of liposomes are compared with those of organic droplets and living cells recorded under the same experimental conditions. We confirmed that general mechanism established for adhesion of hydrocarbon droplets and cells [5] is valid as well for the liposome adhesion within wide range of surface charge densities. Major distinction for the case of liposomes was identified as: (1) different values of critical interfacial tensions of adhesion at the positively and negatively charged electrode, and (2) appearance of adhesion signals even at the lowest surface charge densities of the electrode, revealing the specific interactions of liposome polar head groups and molecular orientation at the electrode [6, 7]. [1] V. Žutić, T. Pleše, J. Tomaić, T. Legović, Mol. Cryst. Liq. Cryst. 113 (1984) 131. [2] V. Svetliičić, V. Žutić, A. Hozić Zimmermann, T. Mišić, Biophys. J., Abstract Issue (2008) 655a. [3] N. Ivošević DeNardis, V. Žutić, V. Svetličić, R. Frkanec, J. Tomašić, Electroanal. 19 (2007) 2444. [4] R. Lipowsky, E. Sackmann (Eds.) Structure and Dynamics of Membranes, Elsevier, Amsterdam, 1995. [5] V. Svetličić, N. Ivošević, S. Kovač, V. Žutić, Langmuir, 16 (2000) 8217. [6] X. Bin, I. Zawisza, J. Goddard, J. Lipkowski, Langmuir 21 (2005) 330. [7] V. Žutić, V. Svetličić, A. Hozić Zimmermann, N. Ivošević DeNardis, R. Frkanec, Langmuir 23 (2007) 8647.

amperometric adhesion signals; DOPC liposomes; dropping mercury electrode; PS liposomes

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