Surface-Functionalization of Plasma-Treated Polystyrene by Hyperbranched Polymers and Use in Biological Applications Alya Boulares-Pender, 1 Andrea Prager-Duschke, 1 Christian Elsner, 1 Michael R. Buchmeiser 1,2 1 Leibniz-Institut fu ¨r Oberfla ¨chenmodifizierung e.V. (IOM), Permoserstr. 15, D-04318 Leipzig, Germany 2 Institut fu ¨ r Technische Chemie, Universita ¨t Leipzig, Linne ´str. 3, D-04103 Leipzig, Germany Received 26 August 2008; accepted 6 December 2008 DOI 10.1002/app.29849 Published online 23 February 2009 in Wiley InterScience (www.interscience.wiley.com). ABSTRACT: Nitrogen plasma was used to amino-func- tionalize polystyrene surfaces, which were further modi- fied via the selective introduction of polyamines suitable for the immobilization of biological compounds. This chemical modification was carried out using a multifunc- tional amine compound linked to glutaraldehyde, leading to the formation of hyperbranched structures at the sur- face. Up to three generations of branched polymers at the polystyrene (PS) surface were created by successive addi- tion of the functional compounds. Amine functions intro- duced at the surface were labeled with 2,3,4,5,6- pentafluorobenzaldehyde and analyzed by X-ray photo- electron spectroscopy (XPS), confirming the successful attachment of each generation of branching. Finally, bovine serum albumin and trypsin were immobilized on N 2 -plasma-treated PS modified with different amounts of branched graft polymer and found to remain bioactive after immobilization. V V C 2009 Wiley Periodicals, Inc. J Appl Polym Sci 112: 2701–2709, 2009 Key words: polystyrene; nitrogen plasma; function- alization; hyperbranched polymers; XPS; derivatization INTRODUCTION In recent years, considerable interest focused on tai- loring commercial polymer surfaces such as polyeth- ylene and polystyrene (PS) for specific biological and biomedical applications, 1,2 e.g., aiming on an increase in the performance of biological assays by the immobilization of biomolecules on the test supports. Indeed, the bulk properties of commercial polymers, e.g., the optical properties as well as hard- ness or conductivity, meet practical requirements for biomedical applications, however, their inert nature makes surface functionalization for the consecutive binding of bioactive compounds inevitable. 1 The immobilization of biomolecules requires either elec- trostatic interaction, affinity interaction, or covalent bonding. In the latter case, the introduction of hydrophilic functionalities at the surface is often envisaged. In their comprehensive study on surface functionalizations for the attachment of bioactive compounds, Goddard and Hotchkiss 1 review vari- ous criteria to be considered in the process of bind- ing biocompounds to the polymer surface, as well as the various techniques in use to this end. The optimization of the surface functionality, in both nature and quantity, for the optimum covalent attachment of the bio-entities at the surface is of primary importance. In this perspective, multifunc- tional agents can be used and various spacer lengths between the surface and the functional groups can be considered. This multifunctionality increases the probability of covalent interactions between proteins and the surface, whereas the spacer distances the functional group away from the bulk surface, 1 allow- ing for a better flexibility of the functional segment, as well as for an improved access of the macromole- cule to be attached. As a result, the biomolecule, e.g., a protein, is more likely to interact efficiently with the hydrophilic functional groups and bond co- valently, whereas it less likely undergoes surface induced denaturation. To increase functionality density at the surface, several types of polymeric structures can be added to or built at the surface, e.g., polymer brushes, 3,4 perfectly spherical or hemispherical dendritic, or randomly hyperbranched structures. 5–9 Den- drimers 10–13 are very attractive due to the multifunc- tionality they can deliver to the surface 14–16 through their perfect geometry. However, this very same geometry can be a drawback since the biomolecule, usually of large dimensions, requires a relative low Journal of Applied Polymer Science, Vol. 112, 2701–2709 (2009) V V C 2009 Wiley Periodicals, Inc. Correspondence to: M. R. Buchmeiser (michael. buchmeiser@iom-leipzig.de). Contract grant sponsors: Federal Republic of Germany and Free State of Saxony.