Recent Publications Feed (ADMIN)

It is well-established that important information about the dissolution and growth of crystals can be obtained by the investigation of step movement on single-crystal faces via in situ AFM. However, a potential drawback of this approach for kinetic measurements is that the small region of investigation may not be representative of the overall surface. It is shown that the investigation of local processes without accounting for the processes outside the region of interest can lead to significant misinterpretation of the data collected. Taking the case of gypsum dissolution as an example, we critically analyze literature data and develop 3 different finite element method models that treat in detail the coupled mass transport–surface kinetic problem pertaining to dissolution processes in a typical AFM environment. It is shown that mass transport cannot be neglected when performing in situ AFM on macroscopic surfaces even with high-convection fluid cells. Moreover, crystal dissolution kinetics determined by AFM is mainly influenced by processes occurring in areas of the surface outside the region of interest. When this is recognized, and appropriate models are applied, step velocities due to dissolution are consistent with expectations based on macroscopic measurements, and the kinetic gap that is often apparent between nanoscale and macroscopic measurements is closed. This study provides a framework for the detailed analysis of AFM kinetic data that has wide utility and applicability.

The ability to make electrochemical measurements under controlled fluid flow has many applications in electrochemical analysis, especially at trace levels. With a move to rapid, on-line, small volume measurements and a need to improve measurement performance, there is a requirement to manufacture more complex fluidic systems with controlled internal 3D geometries at low cost. Both precision machining and lithography typically fail to meet these needs. In this article we describe the role of additive manufacturing (AM) for the fabrication of (micro)fluidic electrochemical flow systems. We show how AM has advanced device manufacture in these areas compared to the more traditional approaches. Different AM methods are also discussed with respect to their capabilities and advantages. A selection of current AM electrochemical flow cell applications are highlighted and future perspectives discussed.

Scanning ion conductance microscopy (SICM) is demonstrated to be a powerful technique for quantitative nanoscale surface charge mapping of living cells. Utilizing a bias modulated (BM) scheme, in which the potential between a quasi-reference counter electrode (QRCE) in an electrolyte-filled nanopipette and a QRCE in bulk solution is modulated, it is shown that both the cell topography and the surface charge present at cellular interfaces can be measured simultaneously at high spatial resolution with dynamic potential measurements. Surface charge is elucidated by probing the properties of the diffuse double layer (DDL) at the cellular interface, and the technique is sensitive at both low-ionic strength and under typical physiological (high-ionic strength) conditions. The combination of experiments that incorporate pixel-level self-referencing (calibration) with a robust theoretical model allows for the analysis of local surface charge variations across cellular interfaces, as demonstrated on two important living systems. First, charge mapping at Zea mays root hairs shows that there is a high negative surface charge at the tip of the cell. Second, it is shown that there are distinct surface charge distributions across the surface of human adipocyte cells, whose role is the storage and regulation of lipids in mammalian systems. These are new features, not previously recognized, and their implications for the functioning of these cells are highlighted.