Fabian M. Koehler

Attachment of EDTA-like chelators to carbon coated metal nanomagnets results in a magnetic reagent for the rapid removal of heavy metals from solutions or contaminated water by three orders of magnitude to concentrations as low as microg L(-1).

Injection of functional nanomagnets in human blood enables selective removal of disease-causing metals, overdosed drugs, and proteins at the (sub-)nanomolar level. This direct in vivo extraction provides a powerful alternative to classical pharmaceutical treatments as disease-causing agents are removed from the organism rather than treating symptoms from exposure. A number of clinically relevant assays demonstrate blood compatibility of the functional nanomagnets.

Beyond the age of silicon: A combination of radical chemistry under standard conditions and clean-room lithography can alter the electronic structure of graphene layers permanently through covalent chemical functionalization. The potential change follows the Hammett correlation. This simple method is a promising approach for graphene-based electronics.

Graphene is a two-dimensional crystalline carbon allotrope that has fascinated researchers worldwide and has extended the interest in carbon structures such as fullerenes and nanotubes. In this Account, we use electrical characterization tools to study chemistry on supported graphene. These experiments elucidate the way covalently bound phenyl units can change graphene’s physical properties. Can we use chemistry to control electronic properties of graphene? What can we learn from well-known carbon allotropes like fullerenes?The surfaces of fullerenes and graphene show distinct differences in reactivity because of the high strain of sp2 carbon in fullerenes compared with the complete lack of strain in graphene. Diazonium chemistry provides a versatile tool for attaching phenyl units covalently to carbon to produce advanced materials and electronic components, but diazonium-based carbon chemistry is strongly influenced by strain. Although fullerenes are highly reactive, graphite (stacks of graphene) remains relatively inert. We chemically introduce n- and p-like doping patterns in two-dimensional graphene using photolithography and extend the ability to chemically control doping to the chemical design of conducting and insulating areas. Thereby we can shape graphene surfaces into functional electronic devices.This Account also describes multistep synthesis on graphene-coated nanoparticles and the introduction of various functional groups on graphene surfaces. Only few functional groups can be produced directly via diazonium chemistry. To overcome this issue, we used these functional groups as starting points for more demanding organic reactions. We covalently attached chelating agents, catalysts, or polymers on the carbon surface. These more complex reactions facilitate the design of electronic modifications, intergraphene connections, and anchors for polymer incorporation. Diazonium chemistry forms strong covalent bridges between graphene and other areas of chemistry.

The present study evaluates the in vitro biomedical performance of an electrospun, flexible, anisotropic bilayer with one layer containing a collagen to mineral ratio similar to that in bone. The double membrane consists of a poly(lactide-co-glycolide) (PLGA) layer and an amorphous calcium phosphate (a-CaP)/collagen (Col)/PLGA layer. In vitro biomineralisation and a cell culture study with human mesenchymal stem cells (hMSC) were conducted to characterise such membranes for possible application as biomaterials. Nanofibres with different a-CaP/Col/PLGA compositions were synthesised by electrospinning to mimic the actual composition of bone tissue. Immersion in simulated body fluid and in cell culture medium resulted in the deposition of a hydroxyapatite layer. Incubation of hMSC for 4 weeks allowed for assessment of the proliferation and osteogenic differentiation of the cells on both sides of the double membrane. Confocal laser scanning microscopy was used to observe the proper adhesion of the cells. Calcium and collagen content was proven by Alizarin red S and Sirius red assays. Acute cytotoxic effects of the nanoparticles or the chemicals used in the scaffold preparation could be excluded based on viability assays (alamarBlue and alkaline phosphatase activity). The findings suggest possible application of such double membranes is in treatment of bone defects with complex geometries as wound dressing material.