Gomes, InêsFeio, Maria J.Santos, Nuno C.Eaton, PeterSerro, Ana PaulaSaramago, BenildePereira, EuláliaFranco, Ricardo2014-03-212014-03-212012J Nanopart Res (2012) 14:13211388-0764http://dx.doi.org/10.1007/s11051-012-1321-7http://hdl.handle.net/10451/10762© Springer Science+Business Media Dordrecht 2012Controlled electrostatic physisorption of horse heart cytochrome c (Cyt c) onto nanostructured gold surfaces was investigated using Quartz-Crystal Microbalance measurements in planar gold surfaces with or without functionalization using a self-assembled monolayer (SAM) of the alkanethiol mercaptoundecanoic acid (MUA). MUA is a useful functionalization ligand for gold surfaces, shedding adsorbed biomolecules from the excessive electron density of the metal. A parallel analysis was conducted in the corresponding curved surfaces of 15nm gold nanoparticles (AuNPs), using zeta-potential and UV– visible spectroscopy. Atomic Force Microscopy of both types of functionalized gold surfaces with a MUA SAM, allowed for visualization of Cyt c deposits on the nanostructured gold surface. The amount of Cyt c adsorbed onto the gold surface could be controlled by the solution pH. For the assays conducted at pH 4.5, when MUA SAM-functionalized planar gold surfaces are positive or neutral, and Cyt c has a positive net charge, only 13% of the planar gold surface area was coated with protein. In contrast, at pH 7.4, when MUA SAM-functionalized planar gold surfaces and Cyt c have opposite charges, a protein coverage of 28% could be observed implying an adsorption process strongly governed by electrostatic forces. Cyt c adsorption on planar and curved gold surfaces are found to be greatly favored by the presence of a MUA-capping layer. In particular, on the AuNPs, the binding constant is three times larger than the binding constant obtained for the original citrate-capped AuNPs.engSelf-assembled monolayersAlkanethiolsGold surfacesGold nanoparticlesCytochrome cQuartz crystal microbalancejournal article