One of the central challenges in nanotechnology is the development of flexible and efficient methods for creating ordered structures with nanometre precision over an extended length scale. Supramolecular self-assembly on surfaces offers attractive features in this regard: it is a 'bottom-up' approach and thus allows the simple and rapid creation of surface assemblies, which are readily tuned through the choice of molecular building blocks used and stabilized by hydrogen bonding, van der Waals interactions, pi-pi bonding or metal coordination between the blocks. Assemblies in the form of two-dimensional open networks are of particular interest for possible applications because well-defined pores can be used for the precise localization and confinement of guest entities such as molecules or clusters, which can add functionality to the supramolecular network. Another widely used method for producing surface structures involves self-assembled monolayers (SAMs), which have introduced unprecedented flexibility in our ability to tailor interfaces and generate patterned surfaces. But SAMs are part of a top-down technology that is limited in terms of the spatial resolution that can be achieved. We therefore rationalized that a particularly powerful fabrication platform might be realized by combining non-covalent self-assembly of porous networks and SAMs, with the former providing nanometre-scale precision and the latter allowing versatile functionalization. Here we show that the two strategies can indeed be combined to create integrated network-SAM hybrid systems that are sufficiently robust for further processing. We show that the supramolecular network and the SAM can both be deposited from solution, which should enable the widespread and flexible use of this combined fabrication method.

6-Mercaptopurine-coated gold nanoparticles (6MP-AuNPs) have been prepared by modification of the nanoparticle surface with 6MP upon displacement of the protective layer of citrate anions. The modification has been studied by UV-vis and FTIR spectroscopies. A study of the stability of these 6MP-AuNPs in aqueous solutions as a function of ionic strength and pH has shown the importance of the charges on the stabilization. The protonation of N9 of the 6MP molecules brings about a sudden flocculation phenomenon. However, the flocculation is reversible upon changing the pH to values where the molecules become newly charged. Evidence of the competence between the interaction of capping solvent molecules and the attractive forces between particles is also shown in this paper.

The protein−gold nanoparticle bioconjugates are playing an important role in the studies of biological systems. The nature of the interaction and the magnitude of the binding affinity together with the conformational changes in the protein upon binding are the most addressed topics in relation to the uses of the bioconjugates in different organisms. In this work, we study the human serum albumin (HSA) protein−gold nanoparticle (AuNP) interactions focusing on the nature of the gold nanoparticle surface modification. We have found that the interactions of the HSA with the AuNPs are mainly electrostatic and that the concentration of protein necessary to stabilize the conjugates decreases when the overall negative charge on the nanoparticle surface increases. The changes in the localized surface plasmon resonance (LSPR) signals of the gold nanoparticles (13 nm diameter) are used to determine the number of protein molecules necessary to stabilize the conjugates in a high ionic strength medium. Fluorescence spectroscopy (stationary and time-resolved) is used to characterize the different bioconjugates and determine the binding constants under different experimental conditions. Moreover, the use of an extrinsic fluorescence probe (1-anilino-8-naphthalenesulfonic acid, ANS) gives us some information about the existence of partial unfolding of the protein upon binding to the nanoparticle.

No abstract