Nanodiamond surface as a photoluminescent pH sensor

Abstract

Abstract A systematic spectroscopic characterization of highly homogeneous water suspensions of ‘buckydiamonds’ comprising sp3 cubic nanodiamond (ND) core covered with disordered sp2 shell densely decorated with oxygen-containing groups demonstrates the excitation-wavelength-dependent photoluminescence (PL) given by at least four types of specific structures on the ND surface (hydroxyl, C=O containing ketones, carboxylic anhydrides, and carboxyl groups). PL properties of NDs suspensions possess concentration-dependent behavior revealing tendency of NDs to agglomerate. PL of NDs has been found to be strongly sensitive to pH of the environment in wide range of pH values, i.e. 2–11. We disclosed the mechanisms of pH sensitivity of the ‘buckydiamond’ and proved that it can serve as all-optical sensor of tiny pH variations suitable for further exploitation for pH sensing locally in the area where NDs have been delivered for any purpose, e.g. bioimaging or therapeutic needs.