L-Histidine-modified biocompatible zinc oxide nanocrystals

In this article, we report a new method of preparing size-controlled and well-dispersed ZnO nanocrystals using L-histidine as the capping agent. The synthesis and properties of ZnO nanocrystals capped with L-histidine prepared by the wet chemical route are presented. The structural properties of L-histidine-capped nanocrystals are investigated by XRD, TEM, EDAX and FTIR spectroscopy. The optical characterisation of the nanocrystals is carried out on the basis of UV-Vis absorption and photoluminescence spectroscopy. The size of the L-histidine-capped ZnO nanocrystals is less than 10nm as confirmed from TEM images. The elemental composition detected from EDAX establishes the presence of the capping agent in the samples. For L-histidine-modified ZnO nanocrystals, the UV absorption edge shifts towards the blue region compared to pure ZnO, suggesting the formation of nanocrystals of smaller size. The intense photoluminescence emission observed around 527nm for L-histidine-capped ZnO offers high prospects in bio-imaging applications. The colloidal stability of the capped nanocrystals is very good as it remains stable without settling down for more than three weeks. Nanocrystals of different sizes have also been synthesised and their properties studied. The present synthesis route is of low cost and easy to control offering high purity to the products, using only bio-compatible materials. The functionalised nanoparticles are suitable for biological applications.