Correction of flotation coefficients, derived from ultracentrifugation, for pressure and concentration

Flotation coefficients are usually determined from data obtained under high pressure (cell bottom) conditions. A power series expansion is proposed for correction to atmospheric pressure (meniscus) conditions. The same expansion may be applied to the concentration correction of flotation coefficients

Single cell electroporation using microfluidic devices

Electroporation is a powerful technique to increase the permeability of cell membranes and subsequently introduce foreign materials into cells. Pores are created in the cell membrane upon application of an electric fi eld (kV/cm). Most applications employ bulk electroporation, at the scale of 1 mL of cells (ca. one million cells). However, recent progresses have shown the interest to miniaturize the technique to a single cell. Single cell electroporation is achieved either using microelectrodes which are placed in close vicinity to one cell, or in a microfl uidic format. We focus here on this second approach, where individual cells are trapped in micrometer-size structures within a microchip, exposed in situ to a high electric fi eld and loaded with either a dye (proof-of-principle experiments) or a plasmid. Specifi cally, we present one device that includes an array of independent electroporation sites for customized and successive poration of nine cells. The different steps of the single cell electroporation protocol are detailed including cell sample preparation, cell trapping, actual cell poration and on-chip detection of pore formation. Electroporation is illustrated here with the transport of dyes through the plasma membrane, the transfection of cells with GFP-encoding plasmids, and the study of the ERK1 signaling pathway using a GFP–ERK1 protein construct expressed by the cells after their transfection with the corresponding plasmid. This last example highlights the power of microfl uidics with the implementation of various steps of a process (cell poration, culture, imaging) performed at the single cell level, on a single device

Determination of the electroporation onset of bilayer lipid membranes as a novel approach to establish ternary phase diagrams: example of the L-α-PC/SM/cholesterol system

The lipid matrix of cell membranes contains phospholipids belonging to two main classes, glycero- and sphingolipids, as well as cholesterol. This matrix can exist in different phases, liquid disordered (l(d)), liquid ordered (l(o)) and possibly solid (s(o)), or even a combination of these. The precise phase composition of a membrane depends on its molecular content and more specifically on the presence and amount of cholesterol. This in turn dictates the membrane properties. In this work, the resistance of membranes to the process of electroporation is studied and related to the membrane phase composition. Specifically, the threshold voltage for electroporation is measured (V-th) when DC pulses with increasing amplitude are applied to membranes prepared from various mixtures of a glycerolipid (Heart PC (L-alpha-PC)), a sphingolipid (Egg SM (SM)) and cholesterol (Ch), introduced in various ratios. Binary mixtures (L-alpha-PC/Ch, L-alpha-PC/SM, SM/Ch) and L-alpha-PC/SM/Ch ternary mixtures are successively employed. For all binary and ternary systems, dramatic changes in V-th are measured as a function of the membrane molecular composition, and the variation patterns of V-th are successfully correlated with the membrane phase composition. Interestingly, the measure of the electroporation onset can be employed as a novel methodology to establish ternary phase diagrams, and this is illustrated with the L-alpha-PC/SM/cholesterol ternary system

Towards simultaneous electrical and optical investigation of BLMS using a novel microfluidic device

We firstly describe the influence of the phospholipid (PL) composition of bilayer lipid membrane on their electrical properties: (i) the more unsaturations in the tail, the earlier the BLM breakdown and (ii) the bulkier the head group, the less stable the membrane. Secondly, we design and fabricate novel devices that couple such electri-cal characterization to optical investigation and that enable the preparation of asym-metrical membranes: a “macro” device including a drilled PMMA plate as well as microfluidic device consisting of a glass-teflon foil-glass sandwich

Parallel single cell analysis on an integrated microfluidic platform for cell trapping, lysis and analysis

We report here a novel and easily scalable microfluidic platform for the parallel analysis of hundreds of individual cells, with controlled single cell trapping, followed by their lysis and subsequent retrieval of the cellular content for on-chip analysis. The device consists of a main channel and an array of shallow side channels connected to the main channel via trapping structures. Cells are individually captured in dam structures by application of a negative pressure from an outlet reservoir, lyzed on site and the cellular content controllably extracted and transported in the individual side channels for on-chip analysis.\u

Visible light emission from reverse-biased silicon nanometer-scale diode-antifuses

Silicon nanometer-scale diodes have been fabricated to emit light in the visible range at low power consumption. Such structures are candidates for emitter elements in Si-based optical interconnect schemes. Spectral measurements of Electroluminescence (EL) on the reverse-biased nanometer-scale diodes brought into breakdown have been carried out over the photon energy range of 1.4-2.8 eV. Previously proposed mechanisms for avalanche emission from conventional silicon p-n junctions are discussed in order to understand the origin of the emission. Also the stability of the diodes has been tested. Results indicate that our nanometer-scale diodes are basically high quality devices. Furthermore due to the nanometer-scale dimensions, very high electrical fields and current densities are possible at low power consumption. This makes these diodes an excellent candidate to be utilized as a light source in Si-based sensors and actuator application

Large area metal nanowire arrays with submicron pitch and tunable sub-20 nm nanogaps

We present a new top-down nanofabrication technology to realize large area metal nanowire (m-NW) arrays with tunable sub-20 nm separation nanogaps without the use of chemical etching or milling of the metal layer. The nanofabrication technology is based on a self-regulating metal deposition process that is facilitated by closely spaced and isolated heterogeneous template surfaces that confines the metal deposition into two dimensions. Electrically isolated parallel arrays of m-NW can be realized with uniform and controllable nanogaps. Au-NW arrays are presented with high-density ~105 NWs cm-1, variable NW diameters down to 50 nm, variable nanogaps down to 5 nm, and very large nanogap length density ~1 km cm-2. A spatially averaged surface enhanced Raman scattering (SERS) analytical enhancement factor of (1.5±0.2)×107 is demonstrated from a benzenethiol monolayer chemisorbed on a Au-NW array substrat