Enhanced Piezocatalysis by Calcium Phosphate Nanowires via Gold Nanoparticle Conjugation

Piezocatalytic materials have considerable application potential in wireless therapy. Most of these applications require biocompatible nanomaterials for in vivo targeting and control of intracellular processes. However, the piezocatalytic performance of a material decreases at a nanometer size regime, and most of the biocompatible materials have poor piezocatalytic efficiency. In particular, hydroxyapatite or calcium phosphate-based nanomaterials have weak piezocatalytic properties that limit the biomedical application potential. Here, we show that anisotropic shape and Au nanoparticle conjugation can enhance the piezocatalytic property of a calcium phosphate nanomaterial by 10 times and the performance approaches that of the bulk/nanoparticle form of well-known BaTiO₃. The colloidal form of calcium phosphate nanowires/nanorods/nanospheres (2-5 nm diameter and 30-1000 nm length) and their Au nanoparticle (5-8 nm) composites are prepared, and their piezoelectric properties have been investigated with piezoresponse force microscopy. It has been observed that the anisotropic nanowire structure of calcium phosphate can enhance the piezoelectric property by 2 times and Au nanoparticle conjugation can enhance it up to 10 times with a piezoelectric constant value of 72 pm/V, which is close to the value of the bulk/nanoparticle form of BaTiO₃. This enhanced piezoelectric property is shown to enhance the piezocatalytic reactions by 10 times. The approach has been used to design colloidal nano-bioconjugate for selective labeling of cancer cells, followed by wireless cell therapy via medical-grade ultrasound-based intracellular reactive oxygen species generation. The developed approach and material can be extended for wireless therapeutic applications and for controlling intracellular processes.