title: Size effect of SnO2nanoparticles on bacteria toxicity and their membrane damage.
abstract: Semiconductor SnO2nanoparticles (NPs) are being exploited for various applications, including those in the environmental context. However, toxicity studies of SnO2NPs are very limited. This study evaluated the toxic effect of two sizes of spherical SnO2NPs (2 and 40 nm) and one size of flower-like SnO2NPs (800 nm) towards the environmental bacteria E. coli and B. subtilis. SnO2NPs were synthesized using a hydrothermal or calcination method and they were well characterized prior to toxicity assessment. To evaluate toxicity, cell viability and membrane damage were determined in cells (1 × 109CFU mL-1) exposed to up to 1000 mg L-1of NPs, using the plate counting method and confocal laser scanning microscopy. Spherical NPs of smaller primary size (E2) had the lowest hydrodynamic size (226 ± 96 nm) and highest negative charge (-30.3 ± 10.1 mV). Smaller spherical NPs also showed greatest effect on viability (IC50> 500 mg L-1) and membrane damage of B. subtilis, whereas E. coli was unaffected. Scanning electron microscopy confirmed the membrane damage of exposed B. subtilis and also exhibited the attachment of E2 NPs to the cell surface, as well as the elongation of cells. It was also apparent that toxicity was caused solely by NPs, as released Sn4+was not toxic to B. subtilis. Thus, surface charge interaction between negatively charged SnO2NPs and positively charged molecules on the membrane of the Gram positive B. subtilis was indicated as the key mechanism related to toxicity of NPs.
authors.affiliation: Centro de Investigación en Materiales Avanzados, Departamento de medio ambiente y energía, Miguel de Cervantes 120, Complejo Industrial Chihuahua, CP 31136 Chihuahua, Chih., Mexico. Electronic address: adriana.chavez@cimav.edu.mx.
authors.forename: Adriana
authors.initials: A
authors.lastname: Chávez-Calderón
authors.affiliation: Centro de Investigación en Materiales Avanzados, Departamento de medio ambiente y energía, Miguel de Cervantes 120, Complejo Industrial Chihuahua, CP 31136 Chihuahua, Chih., Mexico. Electronic address: francisco.paraguay@cimav.edu.mx.
authors.forename: Francisco
authors.initials: F
authors.lastname: Paraguay-Delgado
authors.affiliation: Centro de Investigación en Materiales Avanzados, Departamento de medio ambiente y energía, Miguel de Cervantes 120, Complejo Industrial Chihuahua, CP 31136 Chihuahua, Chih., Mexico. Electronic address: erasmo.orrantia@cimav.edu.mx.
authors.forename: Erasmo
authors.initials: E
authors.lastname: Orrantia-Borunda
authors.affiliation: Centro de Investigación en Materiales Avanzados, Departamento de medio ambiente y energía, Miguel de Cervantes 120, Complejo Industrial Chihuahua, CP 31136 Chihuahua, Chih., Mexico. Electronic address: antonia.luna@cimav.edu.mx.
authors.forename: Antonia
authors.initials: A
authors.lastname: Luna-Velasco
mesh_terms: D001412:Bacillus subtilis / Q000187:drug effects / Q000254:growth & development*; D002462:Cell Membrane / Q000187:drug effects*; D004926:Escherichia coli / Q000187:drug effects / Q000254:growth & development*; D053768:Metal Nanoparticles / Q000633:toxicity*; D008855:Microscopy, Electron, Scanning; D010316:Particle Size; D017971:Tin Compounds / Q000633:toxicity*
chemical_list: D017971:Tin Compounds; C045358:stannic oxide
keywords: Bacteria; Cell viability; Membrane damage; Nanotoxicity; Tin oxide