Localized Supramolecular Peptide Self‐Assembly Directed by Enzyme‐Induced Proton Gradients

Electrodes are ideal substrates for surface localized self‐assembly processes. Spatiotemporal control over such processes is generally directed through the release of ions generated by redox reactions occurring specifically at the electrode. The so‐used gradients of ions proved their effectiveness over the last decade but are in essence limited to material‐based electrodes, considerably reducing the scope of applications. Herein is described a strategy to enzymatically generate proton gradients from non‐conductive surfaces. In the presence of oxygen, immobilization of glucose oxidase (GOx) on a multilayer film provides a flow of protons through enzymatic oxidation of glucose by GOx. The confined acidic environment located at the solid–liquid interface allows the self‐assembly of Fmoc‐AA‐OH (Fmoc=fluorenylmethyloxycarbonyl and A=alanine) dipeptides into β‐sheet nanofibers exclusively from and near the surface. In the absence of oxygen, a multilayer nanoreactor containing GOx and horseradish peroxidase (HRP) similarly induces Fmoc‐AA‐OH self‐assembly.     

On‐Surface Evolution of meso‐Isomerism in Two‐Dimensional Supramolecular Assemblies

Chiral structures created through the adsorption of molecules onto achiral surfaces play pivotal roles in many fields of science and engineering. Here, we present a systematic study of a novel chiral phenomenon on a surface in terms of organizational chirality, that is, meso‐isomerism, through coverage‐driven hierarchical polymorphic transitions of supramolecular assemblies of highly symmetric π‐conjugated molecules. Four coverage‐dependent phases of dehydrobenzo[12]annulene were uniformly fabricated on Ag(111), exhibiting unique chiral characteristics from the single‐molecule level to two‐dimensional supramolecular assemblies. All coverage‐driven phase transitions stem from adsorption‐induced pseudo‐diastereomerism, and our observation of a lemniscate‐type (∞) supramolecular configuration clearly reveals a drastic chiral phase transition from an enantiomeric chiral domain to a meso‐isomeric achiral domain. These findings provide new insights into controlling two‐dimensional chiral architectures on surfaces.     

Site‐Directed,On‐Surface Assembly of DNA Nanostructures

Two‐dimensional DNA lattices have been assembled from DNA double‐crossover (DX) motifs on DNA‐encoded surfaces in a site‐specific manner. The lattices contained two types of single‐stranded protruding arms pointing into opposite directions of the plane. One type of these protruding arms served to anchor the DNA lattice on the solid support through specific hybridization with surface‐bound, complementary capture oligomers. The other type of arms allowed for further attachment of DNA‐tethered probe molecules on the opposite side of the lattices exposed to the solution. Site‐specific lattice assembly and attachment of fluorophore‐labeled oligonucleotides and DNA–protein conjugates was demonstrated using DNA microarrays on flat, transparent mica substrates. Owing to their programmable orientation and addressability over a broad dynamic range from the nanometer to the millimeter length scale, such supramolecular architecture might be used for presenting biomolecules on surfaces, for instance, in biosensor applications.     

Oriented Gold Nanorod Arrays: Self‐Assembly and Optoelectronic Applications

Self‐assembly of anisotropic plasmonic nanomaterials into ordered superstructures has become popular in nanoscience because of their unique anisotropic optical and electronic properties. Gold nanorods (GNRs) are a well‐defined functional building block for fabrication of these superstructures. They possess important anisotropic plasmonic characteristics that result from strong local electric field and are responsive to visible and near‐IR light. There are recent examples of assembling the GNRs into ordered arrays or superstructures through processes such as solvent evaporation and interfacial assembly. In this Minireview, recent progress in the development of the self‐assembled GNR arrays is described, with focus on the formation of oriented GNR arrays on substrates. Key driving forces are discussed, and different strategies and self‐assembly processes of forming oriented GNR arrays are presented. The applications of the oriented GNR arrays in optoelectronic devices are also overviewed, especially surface enhanced Raman scattering (SERS).