Tuning of surface chemical and optical properties of nanodiamonds for biosensing and drug delivery applications

Currently, nanodiamonds (ND) are showing promising perspectives in many research fields due to their inertness, fluorescence, biocompatibility and the possibility to easily functionalize their surface termination. These appealing properties are finding ever-growing interest especially in biomedicine, with potential applications in drug delivery and optical biosensing. The presented work is focused on the enhancement of the Nitrogen-Vacancy (NV) centers fluorescence properties by combining MeV proton irradiation with the surface termination control. To this scope, ion irradiation processes were carried out by exploring a wide range of fluences (10 ¹⁴ - 10 ¹⁷ cm ^-2 ) to create new NV centers, thus allowing to define the conditions maximizing their creation and the emission yield. The collected data were described by a mathematical model predicting the efficiency of the NV center formation as a function of the fluence. This model can be applied not only for the case study described in the present work (MeV proton in ND), but more in general for different ion implantation processes willing to create new NV centers in diamond. Thermal oxidations at different temperatures and times were also carried out on ND to study the evolution of surface chemical groups (DRIFT analysis), as well as their influence on optical properties (Raman / photoluminescence spectroscopy). Besides the general NV centers fluorescence, also NV ^- /NV ⁰ ratio was evaluated at the different processing steps (both in terms of oxidation and irradiation treatments) and the results were interpreted based on DRIFT data. Optically-Detected-Magnetic-Resonance (ODMR) spectra were also acquired to evaluate how treatment conditions influenced the sensitivity of the technique. Finally, surface functionalization with hyaluronic acid conjugates was performed to allow proper stability and dispersibility of ND in solution and to confer targeting ability towards cancer cells. In-vitro tests of cellular uptake and viability were conducted with oxidized and proton-irradiated ND to evaluate their potential as fluorescent probes and drug delivery systems.