Lysine-functionalized nanodiamonds: synthesis, physiochemical characterization, and nucleic acid binding studies

Randeep Kaur,¹ Jackson M Chitanda,² Deborah Michel,¹ Jason Maley,³ Ferenc Borondics,^2,4 Peng Yang,⁵ Ronald E Verrall,² Ildiko Badea<sup>1

1</sup>Drug Design and Discovery Research Group, College of Pharmacy and Nutrition, University of Saskatchewan, ²Department of Chemistry, University of Saskatchewan, ³Saskatchewan Structural Sciences Centre, University of Saskatchewan, ⁴Canadian Light Source, University of Saskatchewan, Saskatoon, SK, Canada; ⁵Department of Organic Chemistry, School of Pharmaceutical Engineering, Shenyang Pharmaceutical University, Shenyang, People's Republic of China

Purpose: Detonation nanodiamonds (NDs) are carbon-based nanomaterials that, because of their size (4–5 nm), stable inert core, alterable surface chemistry, fluorescence, and biocompatibility, are emerging as bioimaging agents and promising tools for the delivery of biochemical molecules into cellular systems. However, diamond particles possess a strong propensity to aggregate in liquid formulation media, restricting their applicability in biomedical sciences. Here, the authors describe the covalent functionalization of NDs with lysine in an attempt to develop nanoparticles able to act as suitable nonviral vectors for transferring genetic materials across cellular membranes.
Methods: NDs were oxidized and functionalized by binding lysine moieties attached to a three-carbon-length linker (1,3-diaminopropane) to their surfaces through amide bonds. Raman and Fourier transform infrared spectroscopy, zeta potential measurement, dynamic light scattering, atomic force microscopic imaging, and thermogravimetric analysis were used to characterize the lysine-functionalized NDs. Finally, the ability of the functionalized diamonds to bind plasmid DNA and small interfering RNA was investigated by gel electrophoresis assay and through size and zeta potential measurements.
Results: NDs were successfully functionalized with the lysine linker, producing surface loading of 1.7 mmol g^-1 of ND. These modified NDs formed highly stable aqueous dispersions with a zeta potential of 49 mV and particle size of approximately 20 nm. The functionalized NDs were found to be able to bind plasmid DNA and small interfering RNA by forming nanosized "diamoplexes".
Conclusion: The lysine-substituted ND particles generated in this study exhibit stable aqueous formulations and show potential for use as carriers for genetic materials.

Keywords: disaggregation, spectroscopy, dispersion, electrophoresis, size, zeta potential