Two-dimensional nanomaterials play a critical role in biology (e.g., lipid bilayers) and electronics (e.g., graphene) but are difficult to directly synthesize with a high level of precision. Peptoid nanosheet bilayers are a versatile synthetic platform for constructing multifunctional, precisely ordered two-dimensional nanostructures. Here we show that nanosheet formation occurs through an unusual monolayer intermediate at the air-water interface. Lateral compression of a self-assembled peptoid monolayer beyond a critical collapse pressure results in the irreversible production of nanosheets. An unusual thermodynamic cycle is employed on a preparative scale, where mechanical energy is used to buckle an intermediate monolayer into a more stable nanosheet. Detailed physical studies of the monolayer-compression mechanism revealed a simple preparative technique to produce nanosheets in 95% overall yield by cyclical monolayer compressions in a rotating closed vial. Compression of monolayers into stable, free-floating products may be a general and preparative approach to access 2D nanomaterials.

The design and synthesis of protein-like polymers is a fundamental challenge in materials science. A means to achieve this goal is to create synthetic polymers of defined sequence where all relevant folding information is incorporated into a single polymer strand. We present here the aqueous self-assembly of peptoid polymers (N-substituted glycines) into ultrathin, two-dimensional highly ordered nanosheets, where all folding information is encoded into a single chain. The sequence designs enforce a two-fold amphiphilic periodicity. Two sequences were considered: one with charged residues alternately positive and negative (alternating patterning), and one with charges segregated in positive and negative halves of the molecule (block patterning). Sheets form between pH 5 and 10 with the optimal conditions being pH 6 for the alternating sequence and pH 8 for the block sequence. Once assembled, the nanosheets remain stable between pH 6 and 10 with observed degradation beginning to occur below pH 6. The alternating charge nanosheets remain stable up to concentrations of 20% acetonitrile, whereas the block pattern displayed greater robustness remaining stable up to 30% acetonitrile. These observations are consistent with expectations based on considerations of the molecules' electrostatic interactions. This study represents an important step in the construction of abiotic materials founded on biological informatic and folding principles.

We have employed electroless deposition to prepare smooth films (mirrors) of silver that could be used as substrates in microcontact printing (μCP) of alkanethiols. Good-quality SAMs of hexadecanethiolate were formed on thin films of electroless silver by printing with an elastomeric stamp; these SAMs were effective resists in protecting the underlying silver from etching in an aqueous ferricyanide solution. Thin films of silver prepared by electroless deposition show a granular morphology (the grain sizes are ∼30−60 nm) and have a rougher surface than those prepared using e-beam or thermal evaporation. As a result, hexadecanethiol liquid spreads more rapidly on electroless silver than on evaporated silver when μCP is carried out in air. This process of reactive spreading limits the resolution and fidelity of pattern transfer to electroless silver films by μCP, but could also be used as a convenient method for reducing the sizes of features of SAMs generated using μCP. The smallest features that we have fabricated using this method were trenches etched in electroless silver (∼40 nm thick) with lateral dimensions of ∼200 nm. The procedure demonstrated here allows us to form micropatterns and microstructures without the metal evaporation usually used to prepare the substrates for μCP, and thus opens μCP and related techniques of microfabrication to those who do not have access to the equipment required for evaporation or sputtering of silver. It also makes it possible to carry out micropatterning on hidden surfaces that could not be silvered by evaporation (for example, the inside surface of a glass tube or flask).

Single-domain antibodies (sdAb), recombinantly produced variable heavy domains derived from the unconventional heavy chain antibodies found in camelids, provide stable, well-expressed binding elements with excellent affinity that can be tailored for specific applications through protein engineering. Complex matrices, such as plasma and serum, can dramatically reduce assay sensitivity. Thus, to achieve highly sensitive detection in complex matrices a highly efficient assay is essential. We produced sdAb as genetically linked dimers, and trimers, each including SpyTag at their C-terminus. The constructs were immobilized onto dyed magnetic microspheres to which SpyCatcher had been coupled and characterized in terms of their performance as capture reagents in sandwich assays. Initial tests on the ability of oriented monomer, dimer, and trimer captures to improve detection versus unoriented constructs in an assay for staphylococcal enterotoxin B spiked into buffer showed the oriented dimer format provided the best sensitivity while offering robust protein production. Thus, this format was utilized to improve a sdAb-based assay for the detection of dengue virus (DENV) nonstructural protein 1 (NS1) in serum. Detection of NS1 from each of the four DENV serotypes spiked into 50% normal human serum was increased by at least a factor of 5 when using the oriented dimer capture. We then demonstrated the potential of using the oriented dimer capture to improve detection of NS1 in clinical samples. This general method should enhance the utility of sdAb incorporated into any diagnostic assay, including those for high consequence pathogens.