The sp³/sp² carbon ratio as a modulator of in vivo and in vitro toxicity of the chemically purified detonation-synthesized nanodiamond via the reactive oxygen species generation

Abstract

Nanodiamonds have been suggested as biocompatible materials and are suitable for various biomedical applications, but little is known about how to synthesize safer nanodiamonds. Herein, seven different detonation-synthesized nanodiamonds (DNDs) with sequential sp³/sp² carbon ratios were assembled by controlling the chemical purification parameters and the role of sp³/sp² carbon ratio on the toxicity of DNDs was investigated. Carbon black and nickel oxide nanoparticles were used as reference particles. The intrinsic reactive oxygen species (ROS) generation potential of DNDs was estimated by a 2′7′-dichlorofluorescein diacetate (DCFH-DA) assay, and these values showed a good negative correlation with the sp³/sp² carbon ratios, which implies that ROS generation increased as the sp³/sp² carbon ratio decreased. As a model to investigate inflammogenic potential of DND samples, a rat intratracheal instillation model was used as the lung is very sensitive to nanoparticle exposures. The sp³/sp² carbon ratios or the estimated values of ROS generation potential showed excellent linear correlations with the number of neutrophils and pro-inflammatory cytokines in bronchoalveolar lavage fluid at 24 h after instillation. Treatment of DND samples to THP-1 derived macrophages also showed that the sp³/sp² carbon ratios or the estimated values of ROS generation potential were closely related with the toxicity endpoints such as cell viability and pro-inflammatory cytokines. Taken together, these data demonstrate that the sp³/sp² carbon ratio is the key determinant for the toxicity of DNDs, which can be a useful tool for the safer-by-design approach of DNDs and the safety assessment of carbon nanoparticles.

Keywords:

• Nanodiamond
• sp³/sp² ratio
• reactive oxygen species
• inflammation
• cytotoxicity

Disclosure statement

The authors declare that they have no competing interests.

Supplemental materials

Supplemental Materials and Methods: The preparation method of the chemically purified DND samples and physicochemical characterization methods including characterization of sp³/sp² carbon ratio, metal impurities, surface chemistry, surface area, zeta potential, hydrodynamic size, endotoxin level, and intrinsic ROS generation potential of DNDs are described.

Additional information

Funding

This research was supported by the BB21+ Project in 2019 and the National Research Foundation of Korea [NRF-2018K1A3A1A74065871 and NRF-2019R1A2C1084489].