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Modulation of non-covalent wet adhesion and cohesion via proximally immobilized non-lysine pair structure

Pengxu Wang,Qing Liu,Wenliang Fu,Chao Zhang,Guiling Cai,Weiwei Xing,Hongliang Dai,Hongya Geng,Donggang Xu

Marine mussels have evolved the secretion of diversified mussel foot proteins to firmly attach to wet, salt-crusty, corroded, and fouled surfaces. Biomimicry of this robust wet adhesion via translating sticky biological molecules is still at an impasse mainly due to the lack of available materials and methodology to fully validate the underline mechanisms of adhesion and cohesion. Increasing sources of evidence have shown that the pair structure of protonated 3,4-dihydroxyphenylalanine (DOPA) and lysine contributes to the adhesion on substrates. However, it is still an uncultivated field to study the roles of those commonly distributed lysine and non-lysine pair structures in the adhesion to different surfaces, while remaining the intermolecular cohesion strength of the pair structures. Herein, the adhesive and cohesive properties of precisely designed single-molecule domains were systematically analyzed using single-molecule force spectroscopy after surface modification of probe tips. It was revealed a record-high adhesion force of ∼ 1000 pN for DOPA-lysine on cation-rich substrates (mica) and tyrosine-Lys on cation-deficient substrates (hydrophilic modified silicon nitride, Si 3 N 4 (OH)) due to an identified hydrophobic force. DOPA-phenylalanine and DOPA-tryptophan pairs were found to show versatile strong adhesion to both cation-rich and -deficient substrates, spanning from 750 pN to 2250 pN. Furthermore, our results revealed that Phe-Lys had an extraordinarily robust cohesion strength, up to 12,000 pN due to cation-π interactions. This study broadens our view of peptides adhesion, provides single molecule proofs toward understanding the mechanism of pair structures in natural adhesive proteins, as well as the design principles of the artificial adhesive layer.