Amino acids nanocrystals for piezoelectric detection of ultra-low mechanical pressure

Developing biocompatible nano-materials with the ability to detect ultra-low mechanical pressure is promising for biomedical sensors. This paper reports the detection of pressure as low as 1 Pa in the environmental pressure of 1 atm (10^-3% pressure change) by nanocrystals of amino acids glycine and alanine through the piezoelectric effect. Piezoelectricity enables detection of pressure by a change of dielectric polarization when the material is subjected to external pressure. This work exploits the non-centro-symmetric structure of some amino acids and their weak hydrogen bonds to develop sensitive mechanical pressure sensors. The β-glycine and l-alanine nanocrystals were grown from aqueous solution inside porous alumina substrate. The nanocrystals exhibit pronounced preferred crystallographic orientation. The sensitive piezoelectric response to ultra-low mechanical pressure is discussed based on atomic and crystal symmetry considerations.