A microfluidic device for high density hydrodynamic cell trapping, growth and super-resolution imaging

Super-Resolution imaging techniques such as Fluorescent Photo-Activation Localisation Microscopy (FPALM) have created a powerful new toolkit for investigating living cells, however a simple platform for growing, trapping, holding and controlling the cells is needed before the approach can become truly widespread. We present a microfluidic device formed in polydimethylsiloxane (PDMS) with a fluidic design which traps cells in a high-density array of wells and holds them very still throughout the life cycle, using hydrodynamic forces only. The device meets or exceeds all the necessary criteria for FPALM imaging of Schizosaccharomyces pombe and is designed to remain flexible, robust and easy to use. © 2011 IEEE.

The deposition of small particles from a turbulent air flow in a curved duct

The paper describes an experimental and theoretical study of the deposition of small spherical particles from a turbulent air flow in a curved duct. The objective was to investigate the interaction between the streamline curvature of the primary flow and the turbulent deposition mechanisms of diffusion and turbophoresis. The experiments were conducted with particles of uranine (used as a fluorescent tracer) produced by an aerosol generator. The particles were entrained in an air flow which passed vertically downwards through a long straight channel of rectangular cross-section leading to a 90° bend. The inside surfaces of the channel and bend were covered with tape to collect the deposited particles. Following a test run the tape was removed in sections, the uranine was dissolved in sodium hydroxide solution and the deposition rates established by measuring the uranine concentration with a luminescence spectrometer. The experimental results were compared with calculations of particle deposition in a curved duct using a computer program that solved the ensemble-averaged particle mass and momentum conservation equations. A particle density-weighted averaging procedure was used and the equations were expressed in terms of the particle convective, rather than total, velocity. This approach provided a simpler formulation of the particle turbulence correlations generated by the averaging process. The computer program was used to investigate the distance required to achieve a fully-developed particle flow in the straight entry channel as well as the variation of the deposition rate around the bend. The simulations showed good agreement with the experimental results. © 2012 Elsevier Ltd.

Measuring EGFR Separations on Cells with ∼10 nm Resolution via Fluorophore Localization Imaging with Photobleaching

Detecting receptor dimerisation and other forms of clustering on the cell surface depends on methods capable of determining protein-protein separations with high resolution in the ∼10-50 nm range. However, this distance range poses a significant challenge because it is too large for fluorescence resonance energy transfer and contains distances too small for all other techniques capable of high-resolution in cells. Here we have adapted the technique of fluorophore localisation imaging with photobleaching to measure inter-receptor separations in the cellular environment. Using the epidermal growth factor receptor, a key cancer target molecule, we demonstrate ∼10 nm resolution while continuously covering the range of ∼10-80 nm. By labelling the receptor on cells expressing low receptor numbers with a fluorescent antagonist we have found inter-receptor separations all the way up from 8 nm to 59 nm. Our data are consistent with epidermal growth factor receptors being able to form homo-polymers of at least 10 receptors in the absence of activating ligands. © 2013 Needham et al.

Prospects of III-nitride optoelectronics grown on Si.

The use of III-nitride-based light-emitting diodes (LEDs) is now widespread in applications such as indicator lamps, display panels, backlighting for liquid-crystal display TVs and computer screens, traffic lights, etc. To meet the huge market demand and lower the manufacturing cost, the LED industry is moving fast from 2 inch to 4 inch and recently to 6 inch wafer sizes. Although Al2O3 (sapphire) and SiC remain the dominant substrate materials for the epitaxy of nitride LEDs, the use of large Si substrates attracts great interest because Si wafers are readily available in large diameters at low cost. In addition, such wafers are compatible with existing processing lines for 6 inch and larger wafers commonly used in the electronics industry. During the last decade, much exciting progress has been achieved in improving the performance of GaN-on-Si devices. In this contribution, the status and prospects of III-nitride optoelectronics grown on Si substrates are reviewed. The issues involved in the growth of GaN-based LED structures on Si and possible solutions are outlined, together with a brief introduction to some novel in situ and ex situ monitoring/characterization tools, which are especially useful for the growth of GaN-on-Si structures.