Self-Assembled 2D Free-Standing Janus Nanosheets with Single-Layer Thickness

Abstract

We report the thermodynamically controlled growth of solution-processable and free-standing nanosheets via peptide assembly in two dimensions. By taking advantage of self-sorting between peptide β-strands and hydrocarbon chains, we have demonstrated the formation of Janus 2D structures with single-layer thickness, which enable a predetermined surface heterofunctionalization. A controlled 2D-to-1D morphological transition was achieved by subtly adjusting the intermolecular forces. These nanosheets provide an ideal substrate for the engineering of guest components (e.g., proteins and nanoparticles), where enhanced enzyme activity was observed. We anticipate that sequence-specific programmed peptides will offer promise as design elements for 2D assemblies with face-selective functionalization.

Figure 1

(a, b) Schematic of F6C11 self-assembly into Janus nanosheets following self-sorting between phenylalanine (blue) and hydrocarbon tails (red). (c) Fluorescence spectra of Nile Red in the presence or absence of F6C11. (d) SIM, (e) TEM, (f) AFM images of nanosheets. The inset in (f) shows the height profile across the marked section indicated by A and B in (f). (g) SAXS profile plot for solution structures of nanosheets (black circles) and fit to lamellar sheets of thickness 4.8 nm (red trace). (h) CD spectrum of nanosheets.

Figure 2

(a) Adsorption of streptavidin on a nanosheet. (b) TEM image of biotin-displaying nanosheets. (c) AFM image of streptavidin-anchored nanosheets. (d, e) AFM height profiles across nanosheet indicated as A and B in (c), respectively, suggesting the size of protein to be ∼5 nm and the single-layer thickness of nanosheet. (f) Surface assembly of HRP on the nanosheet via biotin–avidin affinity, and HRP-catalyzed TMB oxidization. (g) Kinetics of HRP-catalyzed TMB oxidation by H₂O_2..

Figure 3

(a) Schematic and (b) scanning electron microscopy image showing nanosheets functionalized with cysteine and biotin (denoted as “B”) on opposing faces can be immobilized on silicon surfaces and modified with streptavidin-AuNPs. (c) Schematic and (d) SEM image showing nanosheets with cysteine and biotin on the same surface did not undergo specific AuNP binding. Scale bar: (b) 200 nm; (d) 1 μm.

Figure 4

TEM images of nanostructures: (a) F4C11, (b) F5C11, (c) V6C11, and (d) F6C6. Scale bar: (a–c) 100 nm, (d) 500 nm. The arrows in (a) and (b) denote helical features of F4C11 and F5C11 fibrils, respectively.