The unwinding of surfactant-induced helical structure of carboxymethyl amylose by single molecule force spectroscopy

We have employed atomic force microscopy (AFM)-based single molecule force spectroscopy (SMFS) to investigate the unwinding process of the surfactant-induced helical structure of carboxymethyl amylose at the single-molecular level. In doing so, the nanomechanical fingerprint for the conformational transition of carboxymethyl amylose at about 270 pN is used as an indicator for identifying the single chain elongation. Upon the addition of NaCl and cetyltrimethylammonium bromide (CTAB), the force–extension curve of carboxymethyl amylose appears as a long flat plateau during the elongation of a single chain followed by the conformational transition. The flat plateau is attributed to the unwinding process of CTAB-induced helical structure of carboxymethyl amylose. By Gaussian fitting, the center value for plateau height histogram is 17 pN, which reflects the force needed to unwind the CTAB-induced helical structure of carboxymethyl amylose. We hope that this line of research provides an example of using characteristic shoulder plateau of α-linked glycan to identify single chain elongation, allowing for direct measurement of the unwinding force of supramolecular structure using SMFS.