|dc.description.abstract||Traditional submerged exposure method has some drawbacks and limits which may influence test results. An air-liquid-interface (ALI) exposure method can conquer those disadvantages of submerged exposure method, so more and more researchers apply this method to do nanomaterials toxicity test. However, the physical and chemical properties of test materials which may change in the ‘exposure processes’ is rarely be evaluated by ALI exposure method. In addition, the broad-spectrum antimicrobial properties of silver nanoparticles (AgNPs) make its use in numerous household products, water and air puriﬁcation. Researchers also have been investigating the potential toxicity of AgNPs. This research investigated the physical and chemical properties of air phase silver nanoparticles (AgNPs) when they immersed into different liquid, and established an ESP-ALI exposure system to do silver nanoparticles biological toxicity test, and then compared these results with traditional submerged exposure method.
After immersed into DI water, particle size of liquid phase AgNPs would become larger than air phase AgNPs. It presented AgNPs would aggregate dramatically when air phase AgNPs immersed into liquids. Zeta potential of liquid phase AgNPs would approach to -38 mV, and then increase with storage time. In brief, particle size becoming larger and zeta potential showed a negative value implied that its toxicity would decrease when air phase AgNPs immersed into DI water. In terms of water quality, pH and dissolved oxygen in AgNPs suspension solution maintained a constant value with storage time increasing. Thus it implied that air phase AgNPs immersed into DI water would not affect pH and dissolved oxygen of DI water. Conductivity increased with increasing storage time perhaps due to the Ag+ ion release. Furthermore, the released Ag+ concentrations increased almost linearly within 4 hours. After exposure at 4-hour point, Ag+ concentrations of AgNPs suspension would approach to 0.8~1.5 ppb, this concentration range may make some organisms dead.
Furthermore, after immersed into DMEM-H medium, liquid phase AgNPs would aggregate significantly, and particle size can be even larger than one immersed into DI water. This is because under high ionic strength condition, the attractive force between particles became dominant over the repulsive force. Zeta potential of liquid phase AgNPs would approach to -5 mV initially, and then decrease with storage time increasing. In terms of water quality, pH and dissolved oxygen would not change with storage time increasing, and however, conductivity had a trend of rise first and then fall. It may be because Ag+ can bind with Cl- and decrease the ionic strength of sample. Released Ag+ concentrations also had a similar trend with conductivity of AgNPs suspension solution.
Our ESP-ALI exposure system can make cell viability above 80% when exposure time shorter than 3 hours. It presented our ESP-ALI exposure system can use in short exposure experiments. Compared with submerged exposure method, ESP-ALI exposure system only needed lower AgNPs dose to make biomarkers easily detected (cell viability, cell autophagy and apoptosis), and it implied submerged exposure method had a disadvantage of overestimated dose. However, compared with ESP-ALI exposure system, submerged exposure method needed lower dose to induce necrosis, and it implied different stresses on the test cell via different exposure methods might cause different cell death mechanisms.