Ultrasensitive detection of toxic cations through changes in the tunnelling current across films of striped nanoparticles.

Although multiple methods have been developed to detect metal cations, only a few offer sensitivities below 1 pM, and many require complicated procedures and sophisticated equipment. Here, we describe a class of simple solid-state sensors for the ultrasensitive detection of heavy-metal cations (notably, an unprecedented attomolar limit for the detection of CH(3)Hg(+) in both standardized solutions and environmental samples) through changes in the tunnelling current across films of nanoparticles (NPs) protected with striped monolayers of organic ligands. The sensors are also highly selective because of the ligand-shell organization of the NPs. On binding of metal cations, the electronic structure of the molecular bridges between proximal NPs changes, the tunnelling current increases and highly conductive paths ultimately percolate the entire film. The nanoscale heterogeneity of the structure of the film broadens the range of the cation-binding constants, which leads to wide sensitivity ranges (remarkably, over 18 orders of magnitude in CH(3)Hg(+) concentration).

Tomography and static-mechanical properties of adherent cells.

A tomography approach is used to reconstruct 3D cell shapes and, simultaneously, the shapes/positions of the nuclei within these cells. Subjecting the cells to well-defined microconfinements of various diameters allow for relating the steady-state shapes of cells to their static-mechanical properties. The observed shapes show striking regularities between different cell types and all fit to a model that takes into account the cell membrane, cortical actin, and the nucleus.

Thermodynamic manifestations of structure fluctuations in liquids.

Fluctuations of pressure and internal energy in a low-temperature liquid, generated by structure fluctuations, are related in a general and straightforward way to the differences between the long- and short-time thermodynamic susceptibilities. The relations are similar to, but not identical with, those between thermodynamic fluctuations and susceptibilities in classical statistical mechanics. The derivation is general and straightforward, and based on the assumption that the local structure is a slow-relaxing mode in low-temperature liquids and may be characterized by an order parameter.

Structure changes in glassforming liquids upon cooling and compression.

Upon cooling and compression, both the thermodynamic and the kinetic properties of glassformers change. In fragile glassformers, these changes suggest changes in the local structure of the liquid. Thermodynamic data may then provide a measure of structure changes. Special criteria for structure changes in terms of energy and pressure fluctuations in the isochoric system are proposed; recent theoretical results allow one to rewrite the criteria in terms of long- and short-time thermodynamic characteristics of the liquid. Based on the proposed criteria, we discuss the changes in the local structure due to temperature and pressure variations.