Charge and Size‐Dependent Toxicity of Silica Nanoparticles Against <i>Cimex lectularius</i> and <i>Pediculus humanus capitis</i>

ABSTRACT This study evaluated the influence of silica nanoparticle (SiNP) surface charge and size on their toxicity against the common bed bug ( Cimex lectularius ) and the human head louse ( Pediculus humanus capitis ). We compared the insecticidal efficacy of negatively charged SiNPs (inherently negative zeta potential at neutral pH) and positively charged SiNPs (APTES‐modified) of two sizes [66.4 (−42.27 mV) and 68.8 (+13.63 mV) nm vs. 275.1 (−16.33 mV) and 279.6 (+6.54 mV) nm] against these ectoparasites. Laboratory bioassays exposed both species to these nanoparticles, and mortality rates were assessed post‐exposure. Negatively charged SiNPs demonstrated significantly higher toxicity compared to the APTES‐modified, positively charged SiNPs in Pediculus humanus capitis . Indeed, negatively charged SiNPs (66.4 and 275.1 nm) yielded mortality rates of 75% and 66%, while positively charged SiNPs (68.8 and 279.6 nm) resulted in 21.4% and 6.3% mortality. Additionally, in Cimex lectularius , smaller SiNPs (66.4 and 68.8 nm) showed greater toxicity than larger ones (275.1 and 279.6 nm), irrespective of the charge (SiNPs −66.4 and −275.1 nm: 80.0% and 38.3 % vs. SiNPs +68.8 and +279.6 nm: 68.3% and 19.3 %). In conclusion, the surface charge, determined by the presence of APTES modification, and the size of SiNPs are critical factors influencing their insecticidal activity against bed bugs and head lice, with inherently negatively charged, and for bed bugs, smaller, SiNPs appearing more effective, suggesting that tailoring nanoparticle physicochemical properties can enhance targeted pest control strategies.