ORIGINAL CONTRIBUTION Design of silica microparticles with oligopeptide brushes and their interaction with proteins Florin Bucatariu & Frank Simon & Gheorghe Fundueanu & Ecaterina Stela Dragan Received: 20 September 2010 / Revised: 15 October 2010 / Accepted: 18 October 2010 / Published online: 3 November 2010 # Springer-Verlag 2010 Abstract Synthesis of small oligopeptide brushes (oligo(S- benzyl-L-cysteine)) onto polyelectrolyte functionalized silica microparticles was developed. Poly(vinyl amine) (PVAm) adsorbed from salt-free and KCl 10 -1 mol L -1 aqueous solution onto silica microparticles was chemically and naturally cross-linked by epichlorohydrin and CO 2 , respec- tively. After the adsorption of PVAm onto microporous silica particles and stabilization by cross-linking, five repeated coupling reactions of Boc-S-benzyl-L-cysteine were per- formed. To test the protein interactions with the newly designed surface, human serum albumin (HSA) has been selected as a model protein. X-ray photoelectron spectrosco- py, total organic carbon, potentiometric and polyelectrolyte titrations, and electrokinetic analysis were employed to obtain information about the polyelectrolyte adsorption and the amount of the amino acid S-benzyl-L-cysteine that was covalently bound to the solid surface and for determination of the protein amount adsorbed onto functionalized surface. The amount of HSA adsorbed onto modified silica micro- particles decreased in order: silica/PVAm-cross-linked (silica/ PVAm-C) (8.00 mg g -1 ) > silica/PVAm-C/S-benzyl-L-cyste- ine (6.34 mg g -1 ) > silica (4.86 mg g -1 ) > silica/PVAm-C/(S- benzyl-L-cysteine) 5 (1.86 mg g -1 ). Keywords Human serum albumin . Oligopeptide . Polyelectrolyte . Silica . XPS Abbreviations DCC N,N′-dicyclohexylcarbodiimide iep Isoelectric point ECH Epichlorohydrin HSA Human serum albumin pzc Point of zero charge PVAm Poly(vinyl amine) TOC Total organic carbon XPS X-ray photoelectron spectroscopy Introduction Every object interacts with the environment through their surface. Chemical modification of solid surfaces (metal oxides, zeolites, magnetic nanoparticles, colloidal carbon, etc.) by creation of new functional groups produces materials with new properties, which can be utilized in nanofabrication, catalysis, nanolithography, control drug delivery, chromatography, etc. [1–9]. A simple method for control and design certain properties is the adsorption of polyelectrolytes, in monolayer [10–21] or multilayers [22– 33], onto various kinds of solid materials. The polyelectro- lyte chains adsorb onto solid surfaces in a conformation which is related to initial conformation of the macro- molecules in solution [10]. Increasing charge density, the chain becomes stretched, leading to a linear conformation in solution and to thin adsorbed layers onto solid surface. At high polyelectrolyte concentrations, the macromolecules form clusters, and at solid surface, multilayer can be formed [11]. Spange and co-workers deposited the poly(vinyl amine) (PVAm) onto silica, TiO 2 , colloidal carbon, and silicon wafers [13–19]. Various procedures such as “grafting from” and cross-linking surface polymerization and subsequent functionalization of adsorbed PVAm chains have been used. The authors used different cross-linkers to immobilize the F. Bucatariu (*) : G. Fundueanu : E. S. Dragan “Petru Poni” Institute of Macromolecular Chemistry, Aleea Grigore Ghica Voda, 41A, 700487 Iasi, Romania e-mail: fbucatariu@icmpp.ro F. Simon Leibniz Institute of Polymer Research, Hohe Strasse 6, 01069 Dresden, Germany Colloid Polym Sci (2011) 289:33–41 DOI 10.1007/s00396-010-2319-2