A monolayer is a single, closely packed layer of atoms, molecules, or cells. In some cases it is referred to as a self-assembled monolayer. Monolayers of layered crystals like graphene and molybdenum disulfide are generally called 2D materials.
Peptoids, or poly-N-substituted glycines, are a class of biochemicals known as biomimetics that replicate the behavior of biological molecules. Peptidomimetics are recognizable by side chains that are appended to the nitrogen atom of the peptide backbone, rather than to the α-carbons.
A Langmuir–Blodgett trough is a laboratory apparatus that is used to compress monolayers of molecules on the surface of a given subphase and measures surface phenomena due to this compression. It can also be used to deposit single or multiple monolayers on a solid substrate.
A Langmuir–Blodgett (LB) film is a nanostructured system formed when Langmuir films—or Langmuir monolayers (LM)—are transferred from the liquid-gas interface to solid supports during the vertical passage of the support through the monolayers. LB films can contain one or more monolayers of an organic material, deposited from the surface of a liquid onto a solid by immersing the solid substrate into the liquid. A monolayer is adsorbed homogeneously with each immersion or emersion step, thus films with very accurate thickness can be formed. This thickness is accurate because the thickness of each monolayer is known and can therefore be added to find the total thickness of a Langmuir–Blodgett film.
Aqueous biphasic systems (ABS) or aqueous two-phase systems (ATPS) are clean alternatives for traditional organic-water solvent extraction systems.
Microcontact printing is a form of soft lithography that uses the relief patterns on a master polydimethylsiloxane (PDMS) stamp or Urethane rubber micro stamp to form patterns of self-assembled monolayers (SAMs) of ink on the surface of a substrate through conformal contact as in the case of nanotransfer printing (nTP). Its applications are wide-ranging including microelectronics, surface chemistry and cell biology.
A liquid crystalline mesophase is called lyotropic if formed by dissolving an amphiphilic mesogen in a suitable solvent, under appropriate conditions of concentration, temperature and pressure. A mixture of soap and water is an everyday example of a lyotropic liquid crystal.
A model lipid bilayer is any bilayer assembled in vitro, as opposed to the bilayer of natural cell membranes or covering various sub-cellular structures like the nucleus. They are used to study the fundamental properties of biological membranes in a simplified and well-controlled environment, and increasingly in bottom-up synthetic biology for the construction of artificial cells. A model bilayer can be made with either synthetic or natural lipids. The simplest model systems contain only a single pure synthetic lipid. More physiologically relevant model bilayers can be made with mixtures of several synthetic or natural lipids.
Peptide amphiphiles (PAs) are peptide-based molecules that self-assemble into supramolecular nanostructures including; spherical micelles, twisted ribbons, and high-aspect-ratio nanofibers. A peptide amphiphile typically comprises a hydrophilic peptide sequence attached to a lipid tail, i.e. a hydrophobic alkyl chain with 10 to 16 carbons. Therefore, they can be considered a type of lipopeptide. A special type of PA, is constituted by alternating charged and neutral residues, in a repeated pattern, such as RADA16-I. The PAs were developed in the 1990s and the early 2000s and could be used in various medical areas including: nanocarriers, nanodrugs, and imaging agents. However, perhaps their main potential is in regenerative medicine to culture and deliver cells and growth factors.
Silanization of silicon and mica is the coating of these materials with a thin layer of self assembling units.
A Brewster angle microscope (BAM) is a microscope for studying thin films on liquid surfaces, most typically Langmuir films. In a Brewster angle microscope, both the microscope and a polarized light source are aimed towards a liquid surface at that liquid's Brewster angle, in such a way for the microscope to catch an image of any light reflected from the light source via the liquid surface. Because there is no p-polarized reflection from the pure liquid when both are angled towards it at the Brewster angle, light is only reflected when some other phenomenon such as a surface film affects the liquid surface. The technique was first introduced in 1991.
A two-dimensional polymer (2DP) is a sheet-like monomolecular macromolecule consisting of laterally connected repeat units with end groups along all edges. This recent definition of 2DP is based on Hermann Staudinger's polymer concept from the 1920s. According to this, covalent long chain molecules ("Makromoleküle") do exist and are composed of a sequence of linearly connected repeat units and end groups at both termini.
A nanosheet is a two-dimensional nanostructure with thickness in a scale ranging from 1 to 100 nm.
Nanosphere lithography (NSL) is an economical technique for generating single-layer hexagonally close packed or similar patterns of nanoscale features. Generally, NSL applies planar ordered arrays of nanometer-sized latex or silica spheres as lithography masks to fabricate nanoparticle arrays. NSL uses self-assembled monolayers of spheres as evaporation masks. These spheres can be deposited using multiple methods including Langmuir-Blodgett, Dip Coating, Spin Coating, solvent evaporation, force-assembly, and air-water interface. This method has been used to fabricate arrays of various nanopatterns, including gold nanodots with precisely controlled spacings.
In materials science, the term single-layer materials or 2D materials refers to crystalline solids consisting of a single layer of atoms. These materials are promising for some applications but remain the focus of research. Single-layer materials derived from single elements generally carry the -ene suffix in their names, e.g. graphene. Single-layer materials that are compounds of two or more elements have -ane or -ide suffixes. 2D materials can generally be categorized as either 2D allotropes of various elements or as compounds.
In materials science, MXenes are a class of two-dimensional inorganic compounds. These materials consist of a-few-atoms-thick layers of transition metal carbides, nitrides, or carbonitrides. First described in 2011, MXenes combine the metallic conductivity of transition metal carbides with a hydrophilic nature because of their hydroxyl- or oxygen-terminated surfaces.
Titanate (IV) nanosheets (TiNSs) have a 2D structure where TiO6 octahedra are edge-linked in a lepidocrocite-type 2D lattice with chemical formula HxTi2—x/4☐x/4O4 ⦁ H2O (x~0.7; ☐, vacancy). Titanate nanosheets may be regarded as sheets with molecular thickness and infinite planar dimensions. TiNSs are typically formed via liquid-phase exfoliation of protonic titanate. In inorganic layered materials, individual layers are bound to each other by van der Waals interactions if they are neutral, and additional Coulomb interactions if they are composed of oppositely charged layers. Through liquid-phase exfoliation, these individual sheets of layered materials can be efficiently separated using an appropriate solvent, creating single-layer colloidal suspensions. Solvents must have an interaction energy with the layers that is greater than the interaction energy between two layers. In situ X-Ray diffraction data indicates that TiNSs can be treated as macromolecules with a sufficient amount of solvent in between layers so that they behave as individual sheets.
Before the emergence of electron microscopy in the 1950s, scientists did not know the structure of a cell membrane or what its components were; biologists and other researchers used indirect evidence to identify membranes before they could actually be visualized. Specifically, it was through the models of Overton, Langmuir, Gorter and Grendel, and Davson and Danielli, that it was deduced that membranes have lipids, proteins, and a bilayer. The advent of the electron microscope, the findings of J. David Robertson, the proposal of Singer and Nicolson, and additional work of Unwin and Henderson all contributed to the development of the modern membrane model. However, understanding of past membrane models elucidates present-day perception of membrane characteristics. Following intense experimental research, the membrane models of the preceding century gave way to the fluid mosaic model that is accepted today.
Nanoparticle deposition refers to the process of attaching nanoparticles to solid surfaces called substrates to create coatings of nanoparticles. The coatings can have a monolayer or a multilayer and organized or unorganized structure based on the coating method used. Nanoparticles are typically difficult to deposit due to their physical properties.
Francesco Caruso is Melbourne Laureate Professor and National Health and Medical Research Council (NHMRC) Senior Principal Research Fellow in the School of Chemical and Biomolecular Engineering at the University of Melbourne, Australia. Caruso is Deputy Director of the Australian Research Council (ARC) Centre of Excellence in Convergent Bio-Nanoscience and Technology.
