Covalent immobilization of human serum albumin onto reactive polypyrrole-coated polystyrene latex particles

Abstract

Polypyrrole-coated polystyrene latex particles bearing reactive N-succinimidyl functional groups (PS-PPyNSE) were prepared by the in-situ copolymerization of pyrrole (Py) and the active ester-functionalized pyrrole (PyNSE) in the presence of 1 µm diameter-sized polystyrene (PS) latex particles. These particles were prepared by dispersion polymerization of styrene using poly(N-vinylpyrrolidone), PNVP, as a steric stabilizer. The initial comonomer fractions (in mol%) were 25/75, 50/50 and 75/25 for pyrrole and pyrrole-NSE, respectively. The functionalized polypyrrole-coated PS particles (PS-PPyNSE) were characterized in terms of their particle size and surface morphology using transmission electron microscopy (TEM). Infrared and X-ray photoelectron spectroscopy (XPS) detected pyrrole-NSE repeat units at the surface of the latex particles, indicating that this monomer had indeed copolymerized with pyrrole. Furthermore, the core–shell structure of the PS-PPyNSE particles was confirmed by etching the polystyrene core in THF, leading to the formation of hollow conducting polymer capsules. Reactivity of the PS-PPyNSE75 particles was investigated using 2-aminoethanol and 2-mercaptoethanol, two model molecules bearing functional groups borne by proteins. Incubation of the particles with these model molecules clearly showed that the particles are reactive towards amine and thiol groups leading to the formation of interfacial amide and thioester bonds, respectively. The PS-PPyNSE particles were further evaluated as bioadsorbents of human serum albumin (HSA) used as a test protein. It was shown that the HSA macromolecules were immobilized at the surface of PS-PPyNSE particles by forming interfacial amide groups. Incubation of the HSA-grafted latex particles with anti-HSA resulted in immediate flocculation. This indicates that, despite probable conformational changes resulting from contact with NSE-functionalized latexes, HSA proteins retain their biological activity when immobilized on the particle surface. These PS-PPyNSE particles are therefore alternative candidates for visual diagnostic assays.