Cytotoxicity and physicochemical properties of hafnium oxide nanoparticles

Nano-sized hafnium oxide (HfO2) particles are being considered for applications within the semiconductor industry. However, little is known about their cytotoxicity. The objective of this work was to assess several HfO2 nanoparticles (NPs) samples for their acute cytotoxicity. Dynamic light scattering analysis of the samples indicated that the average particle size of the HfO2 in aqueous dispersions was in the submicron range with a fraction of particles having nano-dimensions. The media used in the toxicity assays decreased or increased the average particle size of HfO2 NPs due to dispersion or agglomeration. Static time-of-flight secondary ion mass spectrometry (ToF-SIMS) revealed numerous surface contaminants on the NPs. Only one HfO2 sample caused moderate cytotoxicity to human cell lines. The inhibitory sample caused a 50% response in the Live/Dead assay with HaCaT skin cells at 2200 mg L-1; and a 50% response in the mitochondrial toxicity test at 300 mg L-1. A microbial inhibition assay based on methanogenic activity also revealed that another HFO2 sample caused moderate inhibition. The difference in toxicity between samples could not be attributed to size. Instead the difference in toxicity was likely due to differences in the contaminants of the HfO2. The ToF-SIMS analysis indicated unique signatures of Br and P in the sample toxic to human cell lines suggesting a distinct synthesis was used for that sample which may have been accompanied by inhibitory impurities. The results taken as a whole indicate that HfO2 itself is relatively non-toxic.

► HfO2 nanoparticles were found to have low cytotoxicity.
► Contaminants may have been responsible for cytotoxicity in selected HfO2 samples.
► HfO2 particle size was influenced by aggregating effects of the culture medium.