Long-term stability characteristics of metal nanoparticle generator using small ceramic heater for inhalation toxicity studies

The use of silver nanoparticles is rapidly growing in various industries. However, exposure to nano-sized silver particles generated during production, use, and disposal in ambient air or the workplace remains an important concern for public and occupational health. There are currently no specific methods for measuring the inhalation toxicity of nanoparticles or specific nanoparticle generation methods. In a previous study, silver nanoparticles were generated using a small ceramic heater with a local heating area that allowed direct heating of the bulk silver source, thereby eliminating any space between the heating unit and the source material such that the volume of the nanoparticle generator and power consumption are both remarkably reduced. Therefore, to evaluate the efficacy of this nanoparticle generator for inhalation toxicity studies, the long- term particle generation characteristics were investigated, and the results confirmed a very stable continuous operation over 20-30 h. The geometric mean diameter and total number concentration of nanoparticles remained stable for about 24 h when the initial loaded mass of bulk silver on the heater surface was 160 mg. The particle size distribution after a long operating time was then estimated when changing the initial mass of bulk silver on the heater surface. It took about 36 h for the loaded silver mass to decrease from 160 mg to 100 mg, during which time the geometric mean diameter of the nanoparticles only decreased 6%, from 14 nm to 13.2 nm.