Designing Nanodiamonds for Sensing Applications

Diamond, long known for its thermal conduction, hardness, and clarity, has garnered attention for use in solid-state devices due to the recent development of high-purity growth techniques. Nanometer sized diamond particles, known as nanodiamonds, are particularly exciting due to their biocompatibility, non-toxicity nature, and high chemical and photo stability. Nanodiamonds have intrinsic photoluminescence from many defects one being a so–called nitrogen-vacancy center, which has an extra electron that is sensitive to the surrounding magnetic field. The orientation of the electron spin is reflected in the intensity of the emitted fluorescence and acts as a single photon emitter. This makes nanodiamonds potentially useful in many biomedical applications, such as fluorescent labeling and high resolution imaging. Photobleaching of unknown fluorophores during laser excitation results in background noise during single photon detection. The background fluorescence is suspected to come from surface effects and nanodiamonds are particularly sensitive to this effect due to their large surface area to volume ratio. Currently, the protocol for eliminating photobleaching is to raster over the surface of the diamonds with a high intensity laser, a time consuming process. Here we try to minimize the need for photobleaching by treating the diamond surface with various cleaning technique on nanodiamond. First we created a calibration curve relating nanodiamond concentration to light absorption. We use this to obtain approximate sample concentration after surface cleaning and measure photoluminescence for various concentrations before and after surface cleaning. The surface charge was also characterized using the zeta potential, a measure of the surface charge, to monitor change in surface chemistry. Results from these studies will aid in creating a new protocol for cleaning diamond surface for single photon studies.