Surfaces with Switchable Properties
Massachusetts Institute of Technology (Cambridge, MA) earned U.S. Patent 7,648,739 for switchable surfaces. A multi-university team of chemical engineers have created nanolayers with reversibly switchable properties, for instance, the surface may switch from hydrophobic to hydrophilic.
The surface is comprised of a nanolayer of a material that switches from a first conformation state to a second conformation state when an external stimulus is applied. When the nanolayer is in the first conformation state, the surface is characterized by a first property, and when the nanolayer is in the second conformation state, the surface is characterized by a second property.
The change in conformation state may include a change from a cis to a trans configured double bond, rotating a molecular group about an axis, opening a hinged molecular group, bending a molecular chain, and unbending a molecular chain, according to inventors University of Michigan Chemical Engineering Professor Joerg Lahann, University of California Santa Barbra Chemical Engineering Professor Samir S Mitragotri and MIT Chemical Engineering Professor Robert S. Langer,
When the stimulus is applied, the nanolayer shifts from a first absorption affinity to a second absorption affinity. The method also consists of causing the nanolayer to shift from the second adsorption affinity to the first adsorption affinity. The affinity may be for a surfactant, water, a predetermined analyte, a biomolecule, a small molecule, or a bioactive agent.
The external stimulus may include application of a voltage, a change in an applied voltage, a change in temperature or pH, exposure to UV light, electromagnetic radiation, or a magnetic field, removal of a magnetic field, a change in capacitance, application or removal of an electrostatic charge, or any combination of the above.
The molecular assembly may further include an active group that interacts with the external stimulus and a tether that changes from a first conformation to a second conformation when the active group interacts with the external stimulus. When the tether has the first conformation, the properties of the surface are substantially determined by the first information carrier, and, when the tether has the second conformation, the properties of the surface are substantially determined by the second information carrier.
Either the first information carrier or the second information carrier, or both, may also be one or more of a tether or an active group. Different molecular assemblies having different compositions may be incorporated into a single nanolayer, and the assemblies may be disposed substantially randomly within the nanolayer. Alternatively, the molecular assemblies may be deposited in separate regions by composition, and the external stimulus may be separately applied to the individual regions.
Alternatively, or in addition, the external stimulus may comprise exposure to a ligand, biomolecule, small molecule, bioactive agent, ion, or any combination of these. The stimulus may be applied to a portion of the nanolayer, which portion will undergo a change in conformation state. The nanolayers of the surface are produced by self-assembled monolayers (SAMs).
Much work has been done over the last decade on self-assembled monolayers (SAMs) created on substrates like silicon, silicon dioxide, silver, copper or gold. Research on thiol monolayers on gold surfaces has resulted in technologies such as soft lithography. Applications of SAMs include sensor development, corrosion protection and heterogeneous catalysis. SAMs have been used as templates for organic synthesis and layer-by-layer adsorption.
Their interaction with cells and proteins is well understood and micro-structured SAMs have been used to manipulate cells. All these techniques are based on a common approach: spontaneous monolayer formation of thiols on gold was used to achieve a densely packed two-dimensional crystal which offers reactive head groups for further modification. Chemisorption of thiols on gold occurs as a self-driven process and the packing of the thiols is mainly determined by geometrical aspects.
Due to the spatial limitations and hydrophobic interactions between the alkyl chains, surrounding guest molecules are not expected to migrate into the monolayer. Rather, the head groups are thought to be the frontier line that determines interactions with the surrounding medium. For certain applications in electrode or sensor development, however, a monolayer with an adjustable degree of transparency for small chemical species might be desirable. It is thus desirable to control the density of the monolayer to produce membrane-like structure with a porosity of nanometer-scale.
