Non-Centrosymmetric Single Crystalline Biomolecular Nano-Arrays for Responsive Electronics

Non-centrosymmetric biomolecular crystals, with optical and electrical properties arising from symmetry breaking, hold promise for applications in energy conversion, storage, computing, and biomedicine. However, the synthetic methods used to prepare these crystals are difficult to control and lack reproducibility due to the constraints of working with biomolecules, such as their sensitivity to temperature and the presence of weak intermolecular interactions. Herein, we report a novel strategy for synthesizing ten types of single crystalline amino acid (AA) nanocrystals with control over size (50 nm to 3 μm), anisotropy (particle to rod to wire), and polymorphism (α, β, γ crystalline forms) by leveraging dip-pen nanolithography (DPN) and recrystallization via solvent vapor annealing. This leads to isotropic high-quality crystals that are non-centrosymmetric with strong piezoelectric (g₃₃ coefficients >1000 mV m/N), ferroelectric, and non-linear optical properties. Furthermore, recrystallizing arrays of isotropic AA nanodot features with a binary solvent (water and ethanol) leads to arrays of one-dimensional piezoelectric nanorods with their long axis coincident along the polar axis. To demonstrate the potential of these materials in electronic applications, a mechanically responsive device was fabricated by synthesizing arrays of aligned AA nanorods onto micro-interdigital electrodes. These as-fabricated devices are highly sensitive, responding to ultrasonic stimulation in the form of a piezoelectric response. This work is significant as it opens up opportunities for investigating the fundamental properties of AA nanocrystals, particularly their nanoscale polarization behavior. In addition, it allows one to rapidly assemble and study stimuli-responsive electronics based upon soft biomolecular structures, making them promising candidates for developing biomolecular tools spanning sensors, energy harvesters, and implantable medical devices.