Molecular Interactions of Juvenile and Adult Barnacles at the Polymer Interface

The behavior and mechanisms of marine biofouling─the process by which marine organisms attach onto surfaces in the ocean─have been extensively studied using various biofoulers. Barnacles are often used as model hard fouling organisms, which deposit a proteinaceous adhesive from the shell edge that is later calcified; the side plates and base plates remain on some surfaces even after death. In nature and laboratory settings, barnacles can settle as larvae (cyprids), juveniles, and adults. Much work on barnacle biofouling has focused on characterizing its influence on surface behavior, including inducing crevice corrosion, lowered surface modulus, and dehydration. However, details of the adhesive biomolecules' interaction with fouling surfaces are still under exploration. In this paper, we employed sum frequency generation (SFG) vibrational spectroscopy, a surface-sensitive optical technique that can elucidate molecular behavior at the buried interface between a barnacle and a fouling substrate. Several barnacle/substrate interfaces were studied, using juvenile and adult barnacles, and hydrophobic and hydrophilic substrates with varying complexity. Our results indicated that adhesive proteins were present in both juvenile and adult systems, and the strength, ordering, and structure of these proteins differed between surfaces. Interfacial dehydration occurred when barnacles attached to the nonantifouling surfaces, while surface hydration induced antifouling/fouling-release behavior on zwitterionic coatings. In this study, SFG successfully probed buried barnacle/polymer interfaces, providing vital insight into the hydration mechanisms that are necessary for promoting and deterring bioadhesion and leading the way for future studies between fouling organisms and highly functionalized nonfouling polymers.