BS in Materials Engineering
Materials Engineering Department
Jean L. Lee
Silver and silver-based products are known to cause cytotoxic effects to both microbes and eukaryotic cells. Because of this property, silver nanoparticles (AgNPs) are being studied for their potential in targeted tumor treatments. Previous studies with microbes suggest that AgNPs with cationic capping agents possess enhanced cytotoxicity by virtue of Coulombic attraction between the nanoparticle and the negatively-charged cell wall. Since animal cells possess similar negatively-charged plasma membranes, this research hypothesized that human cells would be more susceptible to positively-charged AgNPs than to negatively-charged AgNPs. To investigate this theory, cancerous cervical cells (HeLa) and healthy fibroblast cells (3T3) were subjected to treatments of 40 nm diameter AgNPs with branched polyethylenimine (AgBPEI, ζ = + 69 mV) and citrate (AgCit, ζ = - 49 mV) capping agents. AgNO3 was also tested to compare AgNP toxicity to that of ionic silver (Ag+). An alamarBlue® viability assay was used to quantify the cytotoxicity of the treatments relative to an untreated control group. AgBPEI displayed a lower LD50 than did Ag+ and AgCit to both cell lines. This suggests AgNP toxicity is not solely from Ag+ dissolution, and also ostensibly supports the initial hypothesis. However, significant AgCit aggregation was observed in culture media, which obfuscates surface charge-based toxicity effects because larger diameter AgNPs are less cytotoxic. Thus size-dependent toxicity must also be considered, although this is not expected to negate surface charge effects. Moreover, since AgBPEI is more stable than AgCit under in vitro conditions, these results suggest that researchers investigating AgNPs for targeted tumor treatments should utilize AgBPEI over AgCit on the premise of enhanced biovailability.