1318 Chem. Commun., 2013, 49, 1318--1320 This journal is c The Royal Society of Chemistry 2013 Cite this: Chem. Commun., 2013, 49, 1318 Protein-assisted 2D assembly of gold nanoparticles on a polysaccharide surface† Laura Taajamaa, a Orlando J. Rojas,* ab Janne Laine, a Kirsi Yliniemi c and Eero Kontturi* a Site-specific assembly of gold nanoparticles on a polysaccharide surface was accomplished via a straightforward method exploiting interfacial polymer blends, selective protein adsorption and electro- static interaction. The method could be useful in further applications due to the universal nature of the utilized phenomena. Site-specific assembly of molecular and supramolecular archi- tectures on 2D systems is a fundamental challenge. 1 Potential uses of such systems include biomedical applications, diagnos- tics, data storage, nanoreactors and sensors. 1a,2 The 2D realm is ever more intriguing when nanoparticles (NPs) are incorpo- rated in these systems, and as a result numerous methods have been published to explicitly decorate surfaces with various NPs. 3 These techniques are often template-based, relying on self-assembly and/or lithography. 3 In addition, organization at a liquid–air interface (Langmuir film) has been extensively used in the construction of 2D NP assemblies. 4 Although numerous accounts exist on arranging NPs on polymer surfaces, we are not aware of any studies that present site-specific NP assemblies on flat polysaccharide surfaces. On the other hand, 2D oligo- and polysaccharide systems are an active field of research 2b,5 with applications in, e.g., analytics, 2b,5,6 drug release 7 and cell encapsulation. 8 Moreover, macroscopic chemical patterning of paper, which is essentially a network of polysaccharide-based fibres, has recently gained attention. 9 Clearly, a facile method to immobilize NPs on flat poly- saccharide surfaces with micro- and nanoscale lateral precision is required. Here, we present the 2D assembly of gold NPs (AuNPs) on specific, micro- and nano-sized sites on an ultrathin polysaccharide film. The method is based on simple physico- chemical phenomena: (i) interfacial phase separation of immis- cible polymer blends, (ii) site-specific adsorption of bovine serum albumin (BSA) protein on polystyrene (PS) on an ultra- thin cellulose film, and (iii) electrostatically driven adsorption of anionic AuNPs on BSA (Fig. 1). The NP textures range from cellular networks to circular patches on cellulose. It is precisely the well-established nature of all these three phenomena that enables the effortlessness of their combination. The current trend towards sustainable solutions promotes the use of renew- able, biodegradable and non-toxic cellulose materials. Further- more, cellulose has the potential for the construction of various 2D architectures. 10 Cellulose films were fabricated by spin coating immiscible PS and trimethylsilyl cellulose (TMSC) blends on silicon crystals followed by selective conversion of the TMSC to cellulose (Fig. S1, ESI†), which does not affect the PS domains in any way. Although hydrophilic, cellulose does not dissolve in water and these films have been shown to be stable in aqueous environments. 10b,c Both protein and AuNP (average diameter ca. 20 nm) adsorption was followed with a Quartz-Crystal Microbalance with Dissipation monitoring (QCM-D) instrument. Schematic of the adsorption process is shown in Fig. 1. Further details of the experimental work performed are described in ESI.† Fig. 2 shows the course of the BSA and AuNP adsorption on the cellulose films. In QCM-D, increasing adsorbed mass is Fig. 1 Simple schematic representation of the protein-assisted 2D assembly of AuNPs. The dimensions are not drawn to scale. a Department of Forest Products Technology, School of Chemical Technology, Aalto University, P.O. Box 16300, FI-00076 Aalto, Finland. E-mail: eero.kontturi@aalto.fi b Department of Forest Biomaterials, North Carolina State University, Box 8005, Raleigh, North Carolina 27695-8005, USA. E-mail: ojrojas@nscu.edu c Department of Chemistry, School of Chemical Technology, Aalto University, P.O. Box 16100, FI-00076 Aalto, Finland † Electronic supplementary information (ESI) available: A detailed description of the experimental work performed, qualitative and quantitative analysis of QCM-D, AFM and XPS results. See DOI: 10.1039/c2cc37288f Received 5th October 2012, Accepted 22nd December 2012 DOI: 10.1039/c2cc37288f www.rsc.org/chemcomm ChemComm COMMUNICATION View Article Online View Journal | View Issue Taajamaa, L., Rojas, O. J., Laine, J., Yliniemi, K., Kontturi, E. (2013) Protein-assisted 2D assembly of gold nanoparticles on a polysaccharide surface, Chem. Commun., 49 (13), 1318-1320. DOI: 10.1039/C2CC37288F. © 2013 Royal Society of Chemistry. Reproduced by permission of The Royal Society of Chemistry.