Please cite this article in press as: S. Wang, et al., Tunable adsorption of bovine serum albumin by annealed cationic spherical polyelectrolyte brushes, Colloids Surf. B: Biointerfaces (2013), http://dx.doi.org/10.1016/j.colsurfb.2013.02.026 ARTICLE IN PRESS G Model COLSUB-5647; No. of Pages 6 Colloids and Surfaces B: Biointerfaces xxx (2013) xxx–xxx Contents lists available at SciVerse ScienceDirect Colloids and Surfaces B: Biointerfaces jou rn al h om epage: www.elsevier.com/locate/colsurfb Short Communication Tunable adsorption of bovine serum albumin by annealed cationic spherical polyelectrolyte brushes Siyi Wang a,1 , Kaimin Chen a,b,1 , A. Basak Kayitmazer c , Li Li a,∗ , Xuhong Guo a,∗ a State Key Laboratory of Chemical Engineering, East China University of Science and Technology, Shanghai 200237, People’s Republic of China b Med-X Research Institute, Shanghai Jiao Tong University, Shanghai 200030, People’s Republic of China c Chemistry Department, Bogazici University, Bebek, Istanbul 34342, Turkey a r t i c l e i n f o Article history: Received 20 September 2012 Received in revised form 11 February 2013 Accepted 15 February 2013 Available online xxx Keywords: Nanoparticles Spherical polyelectrolyte brush Protein adsorption Turbidimetric titration Dynamic light scattering a b s t r a c t By combining turbidimetric titration, dynamic light scattering (DLS), and zeta potential methods, we demonstrated that the adsorption of bovine serum albumin (BSA) in annealed cationic spherical poly- electrolyte brushes (SPB) can be controlled by modulating the pH, ionic strength, BSA concentration of the mixed solution, and SPB thickness. The SPB consist of a polystyrene core with a diameter around 80 nm and a dense shell of poly (2-aminoethylmethacrylate hydrochloride) (PAEMH) with a thickness from 10 to 60 nm covalently attached on the core surface. Results revealed the existence of three pH regions, corresponding to (1) adsorption of BSA in SPB, (2) aggregation of SPB induced by BSA adsorption, and (3) desorption of BSA from SPB. The extent of the pH regions can be modulated by ionic strength, BSA concentration, or SPB thickness. Adsorption measurements demonstrated that the adsorbed amount of BSA in SPB was affected by pH, ionic strength, and SPB thickness. These findings lay the foundation for protein separation by SPB. © 2013 Elsevier B.V. All rights reserved. 1. Introduction Direct adsorption of proteins, enzymes, and antibodies with nanoparticles has recently attracted many interests in biotech- nology [1,2]. Surface functionalized nanoparticles with adsorbed proteins are employed for applications such as drug deliv- ery, surface enrichment, biological labeling, and antibacterial encapsulation [3–5]. Among various nanoparticles, spherical poly- electrolyte brushes (SPB) have been reported to be most suitable for immobilization of proteins in aqueous solutions without defor- mation of native conformation and loss of biological function of proteins [6,7]. SPB provide a stable environment for a highly effi- cient protein immobilization under controlled ionic strength and pH. SPB allow the bound proteins to be released by changing the ionic strength of the medium [7]. Therefore, SPB can serve as tun- able carriers for protein immobilization [8,9], which have potential application in protein separation [10,11] and biological catalysis [12]. Protein uptake on planar brushes have been observed and sum- marized by de Vos et al. [13,14], Czeslik et al. [2,15,16], and Kusumo ∗ Corresponding authors. E-mail addresses: lili76131@ecust.edu.cn (L. Li), guoxuhong@ecust.edu.cn (X. Guo). 1 These authors are contributed equally to this work. et al. [17] They found that the amount of BSA adsorbed was depend- ent on pH, ionic strength [18], protein concentration, and brush grafting density. Adsorption of proteins on anionic spherical poly- electrolyte brushes was studied by Ballauff and his coworkers [7,19,20], who observed an unexpected phenomenon: adsorption of acidic proteins onto anionic SPB took place on the “wrong” side of the isoelectric point of proteins (pI) as evidenced many times by Dubin and his co-workers [21–23]. To the best of our knowledge, a study on the adsorption of acidic proteins by cationic SPB in the full range of pH can hardly be found in literature. The only report was from Ballauff et al., who used isothermal titra- tion calorimetry to observe the adsorption isotherm of bovine pancreatic ribonuclease A (RNase A) on cationic SPB as a func- tion of temperature and salt concentration at physiological pH 7.2 [24]. In this article, annealed cationic SPB were synthesized by pho- toemulsion polymerization, and used as carriers to immobilize bovine serum albumin (BSA) at various pH values (Scheme 1). The interaction between BSA and SPB at different pH values, ionic strengths, BSA concentrations, and SPB thicknesses were observed by combining turbidimetric titration, dynamic light scattering (DLS), and zeta potential methods. Adsorbed amount of BSA in SPB was measured by UV spectroscopy. An investigation on the adsorp- tion of BSA in SPB in the full pH range at various ionic strengths, BSA concentrations, and SPB thicknesses can lay the foundation for protein separation under optimal conditions. 0927-7765/$ – see front matter © 2013 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.colsurfb.2013.02.026