Protein-Bound Freestanding 2D Metal Film for Stealth Information Transmission.

The welding and sintering of nanomaterials is usually achieved at high temperatures and high pressures. Here, it is found that merging of metal nanoparticles occurs under ambient conditions in an aqueous solution via protein bonding. It is discovered that the silver nanoparticles from the in situ reduction of silver ammonium ions by glucose undergo confined nucleation and growth and are bound by ultrathin amyloid-like β-sheet stacking of lysozyme. This merging of silver nanoparticles creates a freestanding large-area (e.g., 400 cm2 ) 2D silver film at the air/water interface with a purity up to 98% and controls nanoscale thickness. This reaction system is general to other proteins and metals, and shows the great ability for controlled synthesis of highly reflective and highly conductive silver films with elongation nearly 10 times higher than that of pure metal without protein bonding. The ultrathin protein-bonding layer functions as a key mediator to dynamically tune the silver conductance in response to external pressures and strains. The sensors exhibit ultrasensitive capability for stealth transmission of Morse code and for silent speech recording via the detection of tiny vibrations of the human throat. This approach will shed light on the development of protein bonding of a given material for bespoke functions.