An in situ study of metal complexation by an immobilized synthetic biopolymer using tapping mode liquid cell atomic force microscopy

Near-field scanning optical microscopy and tapping mode, liquid cell atomic force microscopy were used to study the conformational changes in simple s hort-chain silica-immobilized biopolymer, poly(L-cysteine) (PLCys), as the polymer was exposed to reducing, metal-rich, and acidic environments, respe ctively, to simulate on-line metal preconcentration. In a reducing environm ent (0.01 M dithiothreitol in pH 7.0 ammonium. acetate buffer), the PLCys f eatures resembled islands on the surface of the glass, 36 +/- 7 mn in heigh t and 251 +/- 60 mn in diameter. Upon exposure to metal (Cd2+ buffered at p H 7.0), the PLCys islands broke up into smaller metal binding clusters whos e features were lower in height, 22 +/- 5 nm, and diameter, 213 +/- 53 nm. Exposure to 0.01 M HCl used for metal stripping resulted in protonation of the polymer chains and further reduction in the polymer height to 12 +/- 5 nm. These changes in molecular structure have given new insight into the me chanisms involved to achieve strong binding as well as rapid, quantitative release of bound metals to flexible short-chain synthetic biopolymers.