2015/10/21

Advanced Materials October 19, 2015: Biomimetic Replication of Microscopic Metal–Organic Framework Patterns Using Printed Protein Patterns

The ability to confine functional materials in controlled locations has enabled technological progress in miniaturizing devices for sensing, catalysis, luminescence, diagnosis, and biomedicine.[1] Metal–organic frameworks (MOFs), also known as porous coordination polymers,[2] are an emerging class of multifunctional porous materials arising from the vast combination of metal atoms and polydentate bridging ligands.[3] MOFs have recently attracted increasing scientific interest due to their structural modularity (e.g., use of different metals, reticular chemistry, post-synthetic modifications) and controlled porosity, making them an ideal platform material for a broad scope of applications.[4] Within the different emerging applications, MOF thin films and patterns containing functional biomacromolecules, such as proteins, hold promise for the generation of biomedical diagnostic tools or lab-on-a-chip devices.[5] To date, the fabrication of MOF biocomposite thin films and patterns has only been achieved by first engineering and spatially controlling the MOF, with the incorporation of the biomolecules as a secondary functionalization step unrelated to the actual MOF growth and patterning.[6] As a result, the current fabrication methods are often complex, time consuming and involve multistep procedures.[7] Recently, we discovered that a wide range of biomacromolecules have the ability to attract several metal ions and organic ligands, resulting in the rapid, biomimetic crystallization of MOFs in aqueous solution (biomimetic MOF mineralization).[8] On the other hand, no MOF particles were formed in the absence of proteins due to the lack of ability to locally concentrate the precursors necessary for MOF particle formation.[8] Herein, we demonstrate that this new concept can offer a rapid route for fabricating MOF thin films and patterns directly from surface bound proteins, to replicate the pattern of the proteins with micrometer-scale resolution (Scheme 1). Essentially, a pattern of proteins, which can be easily created using various lithographic techniques such as contact printing, tip-based nanolithography or photolithography,[9] can be used to promote the spatially controlled growth of MOF biocomposites. Furthermore, functional MOF biocomposite patterns can be rapidly formed on a flexible polymer film, allowing for the patterned functionality to be retained even during bending. We further exploit the potential of this technique by demonstrating that luminescent patterned MOFs can be generated within 30 s from the latent proteins remaining from fingerprint residues. The protein induced biomimetic crystallization of MOF patterns is simple, rapid and effective, and should accelerate the exploitation of MOF-biomacromolecule based systems for applications ranging from biomedical devices to forensic science. more