Adsorption of Modified HIV-1 Capsid p24 Protein onto Thermosensitive and Cationic Core-Shell Poly(styrene)-Poly(N-isopropylacrylamide) Particles † David Duracher, Abdelhamid Elaı ¨ssari,* Franc ¸ ois Mallet, and Christian Pichot Unite ´ Mixte CNRS-bioMe ´ rieux, ENS de Lyon, 46 Alle ´ e d’Italie, 69364 Lyon Cedex 07, France Received March 15, 2000. In Final Form: May 23, 2000 The adsorption of HIV-1 capsid p24 protein bearing six histidine residues (named RH24) onto well- characterized thermosensitive and cationic poly(styrene)-poly(N-isopropylacrylamide) core-shell particles was investigated as a function of temperature, pH, incubation time, and salinity. The maximum amount of adsorbed RH24 was observed when the temperature was above the lower critical solution temperature (LCST) of the hydrogel, whereas a negligible adsorbed amount occurred below the LCST. Adsorption isotherms were then determined above the LCST and exhibited well-defined plateaus, which were pH and ionic strength dependent. Isotherm data were tentatively discussed using the Freundlich power law, from which the standard free enthalpy of protein adsorption was estimated. The adsorption behavior of protein was mainly governed by hydrophobic interactions above the LCST; however, differences between the two latexes gave evidence that electrostatic forces also played a significant role. I. Introduction The choice of latex particles as biomolecule carriers has given rise to a great amount of research on the adsorption of protein molecules onto such dispersed material. 1,2 The adsorption study of proteins onto latexes is indeed quite relevant for at least two aspects. First, the adsorption studies can provide new and relevant information on the affinity between both species involved in the immobiliza- tion process. Second, the latex particles bearing proteic materials, such as antigen, antibody, enzyme, etc., can be used for immuno-separation and immuno-detection of viruses, antibodies, and antigens in biomedical diagnosis. Before any real application is considered in the biomedical field, it is fundamental to know how the selected biomol- ecules interact with the polymeric supports. Biomolecule immobilization at the solid/liquid interface is usually affected by factors such as pH, ionic strength, temperature, surface tension of the medium, charge, and nature of the polymer matrix. Therefore, any variation in one or more of these parameters may cause a drastic change in the adsorption-desorption processes of the considered biomolecules. The adsorption of proteins onto colloidal polymer particles has been extensively investi- gated using bovine serum albumin (BSA), immunoglo- bulins (IgG), fibrinogen, and enzymes. 3-7 The maximum amount of protein adsorbed onto such particles was found to be at the isoelectric point of the protein-covered colloids, rather than that of the isoelectric point of the protein as generally observed. The observed behavior has been interpreted by taking into account the ion participation in the protein adsorption process. 5 In addition, the exchange process between adsorbed and free protein has been studied by Ball et al. 8 who demonstrated the dynamics involved in the exchange event. Globally, the adsorption of proteins onto colloidal polymer particles is governed by hydrophobic interactions 3,6 with low or negligible contribution of attractive electrostatic interac- tions. 9 In fact, protein adsorption can be reduced by increasing the hydrophilicity character of the solid support as reported by several authors. 10-12 Recently, several academic studies have been devoted to the adsorption of proteins onto thermally sensitive latexes. Pioneering work has been reported by Kawaguchi et al. 13 related to human γ-globulin (HGG) adsorption onto negatively charged poly(N-isopropylacrylamide (NIPAM)) microgel particles. They pointed out that the amount of protein increased when increasing the hydrophobic char- acter of the particles which was induced by raising the adsorption temperature. The desorption of protein by lowering the temperature (below the lower critical solution temperature (LCST) of poly(NIPAM)) was found to depend on the incubation time for the adsorption above the LCST. As part of a systematic work dealing with the covalent immobilization of recombinant proteins onto synthetic polymers, this paper aims at reporting on a preliminary study of the adsorption of the modified HIV-1 capsid p24 protein (named RH24, M w ∼ 27 500) onto two cationic poly- (styrene)-poly(NIPAM) core-shell particles as a function of time, temperature, protein concentration, salinity, and pH. The adsorption behavior of this protein was tentatively * To whom correspondence should be addressed. Tel: (33) 72- 72-83-64. Fax: (33) 72-72-85-33. E-mail: Hamid.Elaissari@ens- bma.cnrs.fr. † Part of the Special Issue “Colloid Science Matured, Four Colloid Scientists Turn 60 at the Millennium”. (1) Andrade, J. D.; Hlady, V.; Wei, A. P. Pure Appl. Chem. 1992, 64, 1777. (2) Norde, W.; Lyklema, J. J. Colloid Interface Sci. 1979, 71, 350. (3) Kondo, A.; Higashitani, K. J. Colloid Interface Sci. 1992, 150, 344. (4) Betton, F.; Theretz, A.; Elaı ¨ssari, A.; Pichot, C. Colloids Surf. 1993, 1, 97. (5) Elgersma, A. V.; Zsom, R. L.; Norde, W.; Lyklema, J. J. Colloid Interface Sci. 1990, 138, 145. (6) Galisteo-Gonzalez, F.; Martin-Rodriguez, A.; Hidalgo-Alvarez, R. Colloid Polym. Sci. 1994, 272, 352. (7) Puig, J.; Fernandez- Barbero, A.; Bastos-Gonzalez, D.; Serra Domenech, J.; Hidalgo-Alvarez, R. Surf. Prop. Biomater. 1992, 13, 9. (8) Ball, V.; Huetz, P.; Elaı ¨ssari, A.; Cazenave, J.-P.; Voegel, J.-P.; Schaaf, P. Proc. Natl. Acad. Sci. U.S.A. 1994, 91, 7330. (9) Maramatsu. N.; Kondo. T. J. Colloid Interface Sci. 1992, 153, 23. (10) Okubo, M.; Yamamoto, Y.; Uno, M.; Kamei, S.; Matsumoto, T. Colloid Polym. Sci. 1987, 265, 1061. (11) Suzawa, T.; Shirahama, H. Adv. Colloid Interface Sci. 1991, 35, 139. (12) Revilla, J.; Elaı ¨ssari, A.; Carriere, P.; Pichot, C. J. Colloid Interface Sci. 1996, 180, 405. (13) Kawaguchi, H.; Fujimoto, K.; Mizuhara, Y. Colloid Polym. Sci. 1992, 270, 53. 9002 Langmuir 2000, 16, 9002-9008 10.1021/la0004045 CCC: $19.00 © 2000 American Chemical Society Published on Web 08/09/2000