Labyrinth ice pattern formation induced by near-infrared irradiation.

Patterns are broad phenomena that relate to biology, chemistry, and physics. The dendritic growth of crystals is the most well-known ice pattern formation process. Tyndall figures are water-melting patterns that occur when ice absorbs light and becomes superheated. Here, we report a previously undescribed ice and water pattern formation process induced by near-infrared irradiation that heats one phase more than the other in a two-phase system. The pattern formed during the irradiation of ice crystals tens of micrometers thick in solution near equilibrium. Dynamic holes and a microchannel labyrinth then formed in specific regions and were characterized by a typical distance between melted points. We concluded that the differential absorption of water and ice was the driving force for the pattern formation. Heating ice by laser absorption might be useful in applications such as the cryopreservation of biological samples.

Microfluidic Cold-Finger Device for the Investigation of Ice-Binding Proteins.

Ice-binding proteins (IBPs) bind to ice crystals and control their structure, enlargement, and melting, thereby helping their host organisms to avoid injuries associated with ice growth. IBPs are useful in applications where ice growth control is necessary, such as cryopreservation, food storage, and anti-icing. The study of an IBP's mechanism of action is limited by the technological difficulties of in situ observations of molecules at the dynamic interface between ice and water. We describe herein a new, to our knowledge, apparatus designed to generate a controlled temperature gradient in a microfluidic chip, called a microfluidic cold finger (MCF). This device allows growth of a stable ice crystal that can be easily manipulated with or without IBPs in solution. Using the MCF, we show that the fluorescence signal of IBPs conjugated to green fluorescent protein is reduced upon freezing and recovers at melting. This finding strengthens the evidence for irreversible binding of IBPs to their ligand, ice. We also used the MCF to demonstrate the basal-plane affinity of several IBPs, including a recently described IBP from Rhagium inquisitor. Use of the MCF device, along with a temperature-controlled setup, provides a relatively simple and robust technique that can be widely used for further analysis of materials at the ice/water interface.

Model of pore formation in a single cell in a flow-through channel with micro-electrodes.

Microfluidic channels with embedded micro-electrodes are of growing use in devices that aim to electroporate single cells. In this article we present an analysis of pore evolution in a single cell passing by two planar electrodes that are separated by a nano-gap. The cell experiences an electric field that changes in time, as it goes over the electrodes in the channel. The nano-gap between the electrodes enhances the electric field's strength in the micro-channel, thus enabling the use of low potential difference between the electrodes. By computing the electric field on the surface of the cell we can calculate the pore density, as predicted by the model described by Krassowska and Filev (Biophys. J. 92(2):404-417, 2007). The simulation presented in this article is a useful tool for planning and executing experiments of single-cell electroporation in flow-through devices. We demonstrate how different parameters, such as cell size and the size of the gap between the electrodes, change the pore density and show how electroporation between micro-electrodes on the same plane is different from conventional electroporation between facing electrodes.