The production of nanoparticles (NPs) is increasing rapidly for applications in electronics, chemistry, and biology. This interest is due to the very small size of NPs which provides them with many interesting properties such as rapid diffusion, high specific surface areas, reactivity in liquid or gas phase, and a size close to biomacromolecules. In turn, these extreme abilities might be a problem when considering a potentially uncontrolled exposure to the environment. For instance, nanoparticles might be highly mobile and rapidly transported in the environment or inside the body through a water or air pathway. Accordingly, the very fast development of these new synthetic nanomaterials raises questions about their impact on the environment and human health. We have studied the impact of a model water dispersion of nanoparticles (7 nm CeO2 oxide) on a Gram-negative bacteria (Escherichia coli). The nanoparticles are positively charged at neutral pH and thus display a strong electrostatic attraction toward bacterial outer membranes. The counting of colony forming units (CFU) after direct contact with CeO2 NPs allows for the defining of the conditions for which the contact is lethal to Escherichia coli. Furthermore, a set of experiments including sorption isotherms, TEM microscopy, and X-ray absorption spectroscopy (XAS) at cerium L3 edge is linked to propose a scenario for the observed toxic contact.

Liquid crystals have found wide applications in many fields ranging from detergents to information displays and they are also increasingly being used in the ‘bottom-up' self-assembly approach of material nano-structuration. Moreover, liquid-crystalline organizations are frequently observed by biologists. Here we show that one of the four major lyotropic liquid-crystal phases, the columnar one, is much more stable on dilution than reported so far in literature. Indeed, aqueous suspensions of imogolite nanotubes, at low ionic strength, display the columnar liquid-crystal phase at volume fractions as low as ∼0.2%. Consequently, due to its low visco-elasticity, this columnar phase is easily aligned in an alternating current electric field, in contrast with usual columnar liquid-crystal phases. These findings should have important implications for the statistical physics of the suspensions of charged rods and could also be exploited in materials science to prepare ordered nanocomposites and in biophysics to better understand solutions of rod-like biopolymers.