Thesp(3)/Sp(2)Carbon Ratio As A Modulator Ofin Vivoandin Vitrotoxicity Of The Chemically Purified Detonation-Synthesized Nanodiamond Via The Reactive Oxygen Species Generation

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 sequentialsp(3)/sp(2)carbon ratios were assembled by controlling the chemical purification parameters and the role ofsp(3)/sp(2)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 thesp(3)/sp(2)carbon ratios, which implies that ROS generation increased as thesp(3)/sp(2)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. Thesp(3)/sp(2)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 thesp(3)/sp(2)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 thesp(3)/sp(2)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.