Probing the threshold of membrane damage and cytotoxicity effects induced by silica nanoparticles in Escherichia coli bacteria

Abstract

The engineering of nanomaterials, because of their specific properties, is increasingly being developed for commercial purposes over the past decades, to enhance diagnosis, cosmetics properties as well as sensing efficiency. However, the understanding of their fate and thus their interactions at the cellular level with bio-organisms remains elusive. Here, we investigate the size- and charge-dependence of the damages induced by silica nanoparticles (SiO-NPs) on Gram-negative Escherichia coli bacteria. We show and quantify the existence of a NPs size threshold discriminating toxic and inert SiO-NPs with a critical particle diameter (Φ) in the range 50nm-80nm. This particular threshold is identified at both the micrometer scale via viability tests through Colony Forming Units (CFU) counting, and the nanometer scale via atomic force microscopy (AFM). At this nanometer scale, AFM emphasizes the interaction between the cell membrane and SiO-NPs from both topographic and mechanical points of view. For SiO-NPs with Φ>Φ no change in E. coli morphology nor its outer membrane (OM) organization is observed unless the NPs are positively charged in which case reorganization and disruption of the OM are detected. Conversely, when Φ<Φ, E. coli exhibit unusual spherical shapes, partial collapse, even lysis, and OM reorganization.

Detrimental impact of silica nanoparticles on the nanomechanical properties of Escherichia coli, studied by AFM

“…Then, such a treatment induces the opposite effect of that observed for SiO 2 NPs 100 nm (Q1 = 0.4 MPa, Q3 = 1.6 MPa). SiO 2 NPs 4 nm induced a significant decrease in cell elasticity, in good agreement with the morphological and membrane damage previously shown [17].…”

“…Many studies have focused on the well known antibacterial activity of metal oxide and silver NPs, coping with the charge and size dependency of their interactions without addressing their impact on the mechanical properties of cells [16,28,81]. In our pre vious work, we had shown the existence of a critical diameter (50 nm < U c < 80 nm) below which SiO 2 NPs induce morphological and membrane structural damages eventually leading to the E. coli cell lysis [17]. Here, by combining AFM imaging with spec troscopy mode, we also quantitatively demonstrate that such a toxicity is statistically correlated with modifications in the E. coli elasticity.…”

“…nm [17]. Above this diameter, NPs do not change the overall mor phology of E. coli or its membrane structure.…”

“…Furthermore, despite their easy control in terms of size and surface chemistry, the antibacterial activity of SiO 2 NPs is not well documented and their mechanism of action is still unknown [56 58]. For such NPs, a toxicity towards E. coli was shown to depend on their charge and size [17]. Below a critical diameter U c (50 nm < U c < 80 nm), morphological and membrane structural dam ages eventually led to cell lysis.…”

Facile Fabrication of Highly Dispersed Pd@Ag Core–Shell Nanoparticles Embedded in Spirulina platensis by Electroless Deposition and Their Catalytic Properties

“…cells was analyzed underwater with a multimode AFM (Asylum Research, MFP‐3D) using silicon probes in the Scanasyst mode. To avoid the effect of air drying on the cell surface topography, we recorded the AFM images of samples directly in deionized water . For underwater imaging, the collected samples were resuspended in the deionized water, pipetted onto a cleaned culture dish of the polystyrene (60 mm in diameter), and then flushed with deionized water to remove loose cells.…”