Functionalized gold surfaces with hyperbranched polyglycerols. Studies of application

J. PAEZ; V. BRUNETTI; M. CALDERÓN; M. STRUMIA; R. HAAG

Simposio; XII Simposio Latinoamericano de Polímeros y el X Congreso Iberoamericano de Polímeros; 2010

FUNCTIONALIZED GOLD SURFACES WITH HYPERBRANCHED POLYGLYCEROLS. STUDIES OF APPLICATION.    Julieta I. Paez1, Tobias Becherer2, Tihomir Solomun2, Marcelo Calderón2, Verónica Brunetti1, Miriam C. Strumia1, Rainer Haag2 1 IMBIV-CONICET. Facultad de Ciencias Químicas. Universidad Nacional de Córdoba. Córdoba. Argentina. 2 Institut für Chemie und Biochemie. Freie Universität Berlin. Berlin. Germany. julieta@fcq.unc.edu.ar The less structurally perfect, hyperbranched polymers, synthesized via one-step reactions have been considered as a possible alternative to dendrimers, since structural perfection is not a strict prerequisite for most applications (1). In particular, hyperbranched polyglycerols (hPG) are available on a large scale, and have relatively low polydispersities (2). Nanostructures arising from the combination of hPG with different kind of surfaces have been used for many applications such as catalysis (3), dye solar cell construction (4), or protein resistant surfaces development (5). Herein, we present functionalized gold surfaces using self-assembled hPG. The first synthetic part in our approach consists of a controlled introduction of amino and disulfide groups on hPG, in order to obtain structures capable to attach on gold surfaces by a self-assembling process (Fig. 1). 5kDa-hPG with ca. one disulfide group and different percentages (0, 6.5, 9, and 14 %) of amino groups per hyperbranched molecule were synthesized. Secondly, the attachment of modified-hPG to gold surfaces was achieved following the normal overnight dipping procedure of a gold slide in 1 mM DMF solution of each compound. Afterwards, the modified surfaces were characterized by means of spectroscopic and optical techniques. The effect the amount of amino groups exerts over the properties of the hPG-functionalized gold surfaces was specially analyzed.                       Fig. 1. Derivatization of hPG. Reagents and conditions: i) MsCl, dry pyridine. 0°C- r.t., 18 h; ii) NaN3, dry DMF, 60°C, 72 h; iii) PPh3, THF/water, r.t., 10 days; iv) DCC, DMAP, DMF, r.t., 18 h. The contact angle studies confirm that modified surfaces are highly hydrophilic in all cases, as it should be expected. Besides, the FT-IRRAS measurements show the characteristic absorption signals of the PG moiety and indicated that both amino and disulfide groups probably participate in the adsorption process of modified hPG onto gold surfaces. Moreover, two confocal fluorescence measurements were conducted in two cases with the purpose of evaluating the availability and the accessibility of the amino groups on the surface: one of them involved the specific binding of a short DNA segment whereas the other one consisted on the unspecific adsorption of streptavidin, both molecules were labeled with a fluorescent dye. In both cases, experiments show that the amino groups on the surface still remain available and accessible for the attachment of big biomolecules after the modification. These results are encouraging for the construction of specifically functionalized gold surfaces useful for biosensor platform development. On the other hand, in order to gain insight into new applications for these functionalized surfaces, we have explored its capability to act as protein resistant surfaces by means of Surface Plasmon Resonance studies. The unspecific protein adsorption (%PA) of four proteins (fibrinogen, pepsin, BSA, and lysozyme) onto hPG-functionalized surfaces was tested (Fig. 2). %PA referred to hexadecanethiol (HDT) exhibits an increase with the increase of % amino groups for Fib, Pep, and BSA. It is important to note that only lysozyme is positively charged at working pH (7.4). Thus electrostatic repulsive interactions between lysozyme and hPG-modified surfaces should rise according to an increase of % amino groups. As a consequence, the %PA should be reduced, as it was effectively observed. Interestingly, an introduction of 6.5% amino functionalities does not have any influence on the protein resistant properties of hPG. This is still under further study.                   Fig. 2. Protein adsorption of modified surfaces referred to a HDT surface. Fib: fibrinogen, Pep: pepsin, BSA: albumin, Lys: lysozyme. These preliminary results point out a novel synthetic route to create hybrid materials using hyperbranched structures promising for biosensors platforms and protein resistant surfaces development.  REFERENCES [1] Haag et al. Macromolecules 33, 22 (2000) 8158-8166. [2] Frey et al. Rev. Mol. Biotechnol. 90, (2002) 257-267. [3] Meise et al. ChemSusChem 1, (2008) 637-642. [4] Siegers et al. Solar Energy Materials & Solar Cells 93, (2009) 552–563. [5] Siegers et al. Chem. Eur. J. 10, (2004) 2831-2838.