Optical Detection of Charged Biomolecules: Towards Novel Drug Delivery Systems

This paper presents work done on developing optically-traceable intracellular nanodiamond sensors, where the photoluminescence can be changed by a biomolecular attachment/delivery event. Their high biocompatibility, small size and stable luminescence from their color centers make nanodiamond (ND) particles an attractive alternative to molecular dyes for drug-delivery and cell-imaging applications. In our work, we study how surface modification of ND can change the color of ND luminescence (PL). This method can be used as a novel detection tool for remote monitoring of chemical processes in biological systems. Recently, we showed that PL can be driven by atomic functionalization, leading to a change in the color of ND luminescence from red (oxidized ND) to orange (hydrogenated ND). In this work, we show how PL of ND changes similarly when interacting with positively and negatively charged molecules. The effect is demonstrated on fluorinated ND, where the high dipole moment of the C-F bond is favorable for the formation of non-covalent bonds with charged molecules. We model this effect using electrical potential changes at the diamond surface. The final aim of the work is to develop a "smart" optically traceable drug carrier, where the delivery event is optically detectable.