Figure 4: Deposition of 'footprints' of the temporary protein adhesive secreted by cypris larvae of barnacles during surface exploration as revealed by imaging surface plasmon resonance.

SPR is a spectroscopic, surface analysis technique that allows the adsorption of macromolecules to a metallic surface to be measured and imaged through changes in reflectivity. The two panels show snapshots of gold surfaces after cypris larvae were allowed to explore for 7 min. One of the gold surfaces was coated with methyl-terminated oligo(ethyleneglycol) (mOEG), the other was left as bare gold. On the bare gold surface, the cyprids explored the surface via their sensory antennules and made numerous contact points or 'footprints', shown as bright reflective spots, each of which represents the deposition of small amounts of proteinaceous temporary adhesive from the antennules. On the gold surface, these spots persisted following detachment of the cyprid, implying that the adhesive remained on the surface. In the case of the mOEG substrate, which is well known for its protein-repellent properties, although the cyprids explored the surface, very little proteinaceous residue remains at the contact points, as shown by the few, dull-reflective spots (arrowed). On mOEG, the spots only persisted for as long as the cyprid remained in contact with the surface implying that, on detachment, the protein remained on the antennules. The scale bars in each frame are 100 μm. Reproduced with permission from ref. 28, © 2008 American Vacuum Society.