**Author details**

362 The Complex World of Polysaccharides

network (Figure 13) in filtered seawater.

fibrils in filtered seawater. Two typical curves are shown.

rational design of polysaccharide gels with desired properties.

progress.

accuracy of 0.1nm.

cantilever measures the force on the polymer with an accuracy of ~5 pN, while the piezoelectric positioner records the changes in the molecule's end-to-end length with an

AFM force spectroscopy is widely used method in polymer biophysics allowing measuring mechanical properties of single molecules, and with a possibility to directly quantify the forces involved in both intra- and inter-molecular polymer interactions [90-93]. It is also adopted in advancing diatom research into the nanotechnology era [94]. Most of the work done so far on measuring forces with AFM has distinguished non adhesive and adhesive EPS components and discovered the adhesive properties and designs that give explanation as to why diatoms have the great tendency to attach to surfaces. However, force spectroscopy has not yet been performed on single diatom polysaccharide fibrils or their networks. The data that follows are the results of exploratory experiments conducted on diatom polysaccharide molecules (single fibrils, Figure 12) and on marine gel polysaccharide

**Figure 12.** Force approach (in red) and extension (in blue) curves acquired for polysaccharide single

The extension curve with the two rupture events in Figure 12 could result from the two individual fibrils of different length (0.9 and 1.5 µm) simultaneously attached to the tip. The force spectrum signature for polysaccharide fibrils assembled in marine gel network is by far more complex (Figure 13) [95]. Assigning the underlying disentanglement events is in

The force spectra can provide the critical piece of information that will allow us to characterize and quantify physical forces in polysaccharide network assemblies. Further developments will contribute to the new field of nanoecology and open the possibilities for Ranieri Urbani and Paola Sist *Department of Life Sciences, University of Trieste, Trieste, Italy* 

Galja Pletikapić, Tea Mišić Radić, Vesna Svetličić \* and Vera Žutić *2Division for Marine and Environmental Research, Ruđer Bošković Institute, Zagreb, Croatia* 

## **Acknowledgement**

The work reported in the section "The supramolecular organization of polysaccharide fibrils" was performed within the scope of the project "Surface forces on atomic scale applied in marine science and nanotechnology", Croatian Ministry of Science and the project "Development of a nanotechnology-based targeted recognition system for biomacromolecules", Croatian Science Foundation. AFM force spectroscopy of isolated polysaccharides was performed during G.P. stay in Jasna Brujić Group, Department of

<sup>\*</sup> Corresponding Author

Physics, New York University. G.P. stay was financed through Croatian Science Foundation Doctoral Fellowship Award. Participation of Miklós Kellermayer was made possible through the networking of the COST Action "AFM for Nanomedicine and Life Science".
