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

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.

S2 minutes, repeated twice. The peptides were cleaved using a trifluoroacetic acid/triisopropylsilane/water (95:2.5:2. 5, v/v/v) cleavage solution for 3 hours. Excess TFA was removed by rotary evaporation. The crude peptide was precipitated by cold diethyl ether several times and purified using preparative reverse phase high performance liquid chromatography (HPLC, Shimadzu). A water-acetonitrile gradient was used (95% water to 5%) with 0.1% NH 4 OH added to the mobile phase. The Phenomenex C18 Gemini NX column was 150 x 21.2 mm and had a 5 µm particle size and 110 Å pore size. Matrix-assisted laser desorption spectroscopy (MALDI; Waters) was used to confirm the expected m/z ratio and α-Cyano-4-hydroxycinnamic acid was used as the MALDI matrix substance.
Preparation of 2D peptide nanosheets. Stock solution of 10 mM F6C11 was prepared in hexafluoro-2-propanol (HFIP) to completely break the hydrogen-bonding between peptide molecules. Typically, 10 μL of peptide stock solution was injected quickly into 390 μL of phosphate buffer (10 mM, pH 7). The mixture was vortexed for 10 seconds and stored at room temperature overnight. The solution will become cloudy once the nanosheets are formed.

Preparation of AuNP on nanosheet via thiol-Au bonding.
(1) The thiol-displaying nanosheets were prepared by a co-assembly method as described above. Orius camera. TEM samples were prepared using the negative-staining method. Briefly, a drop was deposited onto the carbon-coated 200 mesh copper grid for 5 min. The excess S4 of solution was wiped away using a filter paper. Subsequently, the grid was stained with a drop of uranyl acetate (1.0 wt%) solution for 3 min. Excess staining agent was removed using a filter paper and the sample dried in air.
Small angle X-ray scattering (SAXS). Small angle X-ray scattering measurements were performed at the Diamond Light Source on beamline I22 with an X-ray energy of 18 keV. The geometry was calibrated using powdered silver behenate. A 0.5 mM suspension of peptide nanosheets in 10 mM phosphate buffer (pH 7.0) was measured in a 1.7 mm quartz glass capillary and the scattered X-ray intensity collected.
The 2-D scattered intensity was masked, calibrated and azimuthally integrated automatically on I22. The resulting plots of scattered X-ray intensity with Q were then generated by subtracting a solvent filled capillary measurement from the sample measurement prior to analysis. The scattering is immediately reminiscent of plate-like structures with an approximately Q -2 decay in the Guinier region which agreed with the structures observed by TEM and AFM. A quantitative assessment of the thickness of the structures was achieved by fitting the scattering data using the SasView fitting software with the LamellarModel which is appropriate for plate-like structures with dimensions much greater than the thickness. The background, lamellar thickness and a scaling factor were allowed to vary during fitting of the scattering data in the region between Q = 0.022 and 0.3 Å -1 . The parameters for the fit can be seen in Table S1.