Communications to the Editor Bull. Korean Chem. Soc. 2013, Vol. 34, No. 12 3541 http://dx.doi.org/10.5012/bkcs.2013.34.12.3541 Direct, Noncovalent Coating of a Gold Surface with Polymeric Self-Assembled Monolayers Hojae Lee, Daewha Hong, Sangyong Jon, † and Insung S. Choi * Department of Chemistry, KAIST, Daejeon 305-701, Korea. * E-mail: ischoi@kaist.ac.kr † Department of Biological Sciences, KAIST, Daejeon 305-701, Korea Received September 4, 2013, Accepted September 12, 2013 Key Words : Biomolecule immobilization, Gold surface, Micropatterns, Non-biofouling, Polymeric self-as- sembled monolayers The spatio-selective immobilization of biomolecules, such as DNAs, antibodies, or aptamers, onto a solid surface is required for the development of bioanalytical and bio- medical devices that interface the immobilized probe with the target biospecifically. 1-4 Strategies for non-covalent and covalent immobilization have been developed, exemplified by biotin-streptavidin 5,6 or N-nitrilotriacetic acid (NTA)- histidine tag interactions 7 for non-covalent linking and N- hydroxysuccinimide (NHS)-mediated amide coupling 8,9 for covalent coupling. In addition to the surface-immobilized bioprobes, the surface should be non-biofouling (i.e., prev- enting or at least minimizing the non-specific adsorption of proteins and other molecules and adherence of cells) for maximized biospecific recognition between the probe and the target and multiplexed detection of the analytes based on microarrays/patterns. In this respect, a method should be developed for providing a surface of interest with three orthogonal properties: functionalizable, non-biofouling, and surface-anchorable ones. We suggested the formation of polymeric self-assembled monolayers (pSAMs) with a ran- dom copolymer having these three properties. 10 For example, a hydrophobic cyclic olefin copolymer (COC) surface was coated with a polymer presenting the non-biofouling poly- (ethylene glycol) (PEG) and NHS moieties along with a long alkyl chain (C12) for surface anchoring of the polymer via hydrophobic interactions (pPNC) (Figure 1). 10d On the other hand, a gold surface has widely been used for bioanalytical characterizations, including surface plasmon resonance (SPR) spectroscopy, 9,11,12 and mostly the surface coating has been achieved by utilizing the gold-thiol inter- actions in the form of SAMs. 13 Although there is the intense need for customized fabrication of a gold surface for bio- recognition, only the SAM-based approach has been available because of the practical difficulty in the synthesis of thiol- presenting random copolymers for the pSAM formation. Instead, we have previously used the random copolymer presenting PEG and NHS, where the NHS moiety acted as both a post-functionalizable group and a surface-anchorable group to amine-terminated SAMs on gold. 14 In this paper, we report that the interactions of alkyl chains with gold are strong enough for coating the gold surface with pSAM of pPNC. Of interest, the pSAM proves fairly stable during the pattern generation of IgG/anti-IgG. The coating of a gold substrate with the pSAM of pPNC was achieved by simply immersing the substrate in the citrate buffer solution of pPNC (10 mg/mL, pH 3.3) for 2 h at ambient temperature. We used the citrate buffer for pPNC, because the NHS group was relatively stable under acidic conditions. The typical static water contact angle of a bare gold was measured to be 59.5 ± 1.3 o in our case, and the water contact angle was changed to 73.3 ± 0.9 o after coating (Figure 2(a)). The coating was further confirmed by the ellipsometric thickness (17.1 Å), after coating. The grazing- angle Fourier transform IR (GA-FTIR) spectrum showed the peaks of pPNC at 3249 (O-H stretching), 1742 (C=O stretch- ing, ester and imide), and 1476 cm -1 (-CH 2 - bending), indi- cating the formation of pSAMs (Figure 2(b)). Figure 1. Structure of pPNC used in this work. Figure 2. (a) Static water contact angles of bare and pPNC-coated gold surfaces. (b) GA-FTIR spectrum of the pPNC-coated gold surface.