Racemic Amino Acid Piezoelectric Transducer.

Single crystal L-amino acids can exhibit technologically useful piezoelectric and nonlinear optical properties. Here we predict, using density functional theory, the piezoelectric charge and strain and voltage tensors of the racemic amino acid DL alanine, and use the modeling data to guide the first macroscopic and nanoscopic piezoelectric measurements on DL-alanine single crystals and polycrystalline aggregates. We demonstrate voltage generation of up to 0.8 V from DL-alanine crystal films under simple manual compression, twice as high as other amino acid crystals. Our results suggest that net molecular chirality is not a prerequisite for piezoelectric behavior in organic crystals. The transducer presented herein demonstrates that DL-alanine crystals can be used in applications such as temperature and force measurement in biosensors, data storage in flexible electronic devices, and mechanical actuation in energy harvesters.

Control of piezoelectricity in amino acids by supramolecular packing.

Piezoelectricity, the linear relationship between stress and induced electrical charge, has attracted recent interest due to its manifestation in biological molecules such as synthetic polypeptides or amino acid crystals, including gamma (γ) glycine. It has also been demonstrated in bone, collagen, elastin and the synthetic bone mineral hydroxyapatite. Piezoelectric coefficients exhibited by these biological materials are generally low, typically in the range of 0.1-10 pm V-1, limiting technological applications. Guided by quantum mechanical calculations we have measured a high shear piezoelectricity (178 pm V-1) in the amino acid crystal beta (ß) glycine, which is of similar magnitude to barium titanate or lead zirconate titanate. Our calculations show that the high piezoelectric coefficients originate from an efficient packing of the molecules along certain crystallographic planes and directions. The highest predicted piezoelectric voltage constant for ß-glycine crystals is 8 V mN-1, which is an order of magnitude larger than the voltage generated by any currently used ceramic or polymer.