Carbon nanodots interference with lactate dehydrogenase assay in human monocyte THP-1 cells

BACKGROUND: Carbon nanodots (CD), a new class of carbon nanomaterials with sizes below 10 nm, have recently attracted wide attention due to their superiority in water solubility, chemical inertness, and resistance to photobleaching. As a result, CD has found important and wide applications in energy, catalysis, biological labeling, bioimaging and drug delivery. On the other hand, due to the lack of available toxicity data, there is a growing concern regarding the potential risks of CD. Hence, accurate assessment of the cytotoxicity of CD has become more important than ever before. The lactate dehydrogenase (LDH) assay is widely used to detect cytotoxicity of various nanoparticles including CD. Many recent studies used LDH assay to study the CD toxicity in various cells. However, these studies failed to further examine whether the CD were interfering with the LDH assay which would alter their findings. FINDINGS: This study investigated the possible interference of carbon nanodots on the LDH assay in human monocyte THP-1 cells. Monocytes are known to be involved in inflammable vascular diseases, and have been suggested to be the targets for CD exposure. In this study, the cytotoxicity of CD in concentrations ranging from 0.075 to 0.60 mg/mL, was determined by using the LDH assay. To validate the results of LDH assay, the cell counting method with trypan blue staining was used. With 24 hours incubation time, the cell viability of THP-1 was significantly decreased according to the trypan blue staining method. Whereas, in the LDH assay, the CD was found to interfere in a dose-dependent manner with the NADH absorbance measurements at 340 nm. CONCLUSIONS: This study represents the first report on the negative interference of CD on LDH assay, and caution should be observed when evaluating the cytotoxicity of CD.