MOFs as multivalent materials: Size control and surface functionalization by monovalent capping ligands
Raquel Mejia-Ariza, Timon Rijnaarts, Richard J. M. Egberink, Wies van Roosmalen, Pascal Jonkheijm and Jurriaan Huskens*
Molecular Nanofabrication Group, MESA+ Institute for Nanotechnology, University of Twente, P.O. Box 217, 7500 AE, Enschede, The Netherlands
Control of particle size and composition are pivotal to tune the properties of metal organic frameworks (MOFs) for biomedical applications. Particle size can be controlled using monovalent capping ligands for the termination of the crystal growth. To understand and control the MOF particle size at the nano-scale, we here apply a 1:1 binding stoichiometry taking into account the valency of the MOF components while varying the ratio between monovalent capping ligand and multivalent bridging ligand. Moreover, the MOF surface is modified with bioactive ligands showing the potential for biomedical applications as a targeting system. To achieve this, MIL-88A has been synthesized by adding a monovalent capping ligand. Size control at the nano-scale was achieved using carboxylic acid-functionalized poly(ethylene glycol) (PEG-COOH) ligands, at different molecular weights and concentrations. Moreover, a biotin-carboxylic acid ligand was used to functionalize MIL-88A to bind fluorescently labeled streptavidin as an example towards bioapplications. Combining these chemical and physical properties, we envisage the use of multifunctional MIL-88A nanoparticles for targeting and drug delivery applications.