Many prospective applications of nanodiamonds (NDs), such as drug delivery or biolabeling, occur in water or physiological media. The characterization of electronic properties of NDs in aqueous solution is therefore fundamental for a better understanding of their behavior in physiologically relevant conditions. However, NDs characterization is generally performed on NDs deposited on a substrate because of the lack of experimental methods to measure electronic properties of NDs in water.The use of soft X-ray absorption spectroscopy (XAS) and emission spectroscopy (XES) in liquid is particularly interesting for this purpose. Combination of tunable intense X-ray photon source of synchrotron with microjet technology has shown to be an efficient method to characterize electronic structure of solutes dispersed in water (1).
In particular, we recently applied this technique to acetate molecule and demonstrated that the carboxylate groups of acetate could be selectively probed to investigate ion pairing with cations in solution (2). Similar experiments on NDs could help understanding drug binding mechanisms in solution for example.In this presentation, first characterization of carboxylated detonation NDs in water by XAS and XES will be presented. Experiments were conducted at the BESSY II third-generation synchrotron facility using a liquid microjet. The carbon K-edge as well as the oxygen K-edge of NDs will be presented and compared to spectra obtained from NDs deposited on a substrate. Based on this comparison, interaction between NDs and water molecules in liquid will be discussed. This study highlights the potential of soft X-ray spectroscopy for characterization of the electronic structure of nanoparticles which can be probed directly in solution.
1. Lange, K. M. & Aziz, E. F. Electronic structure of ions and molecules in solution: a view from modern soft X-ray spectroscopies. Chem. Soc. Rev. 42, 6840-59 (2013).
2. Petit et al, Probing Ion-specific Effects on Aqueous Acetate Solutions: Ion Pairing versus Water Structure Modifications, submitted.