High yield fabrication of chemically reduced graphene oxide field effect transistors by dielectrophoresis

We demonstrate high yield fabrication of field effect transistors (FET) using chemically reduced graphene oxide (RGO) sheets suspended in water assembled via dielectrophoresis. The two terminal resistances of the devices were improved by an order of magnitude upon mild annealing at 200 0C in Ar/H2 environment for 1 hour. With the application of a backgate voltage, all of the devices showed FET behavior with maximum hole and electron mobilities of 4.0 and 1.5 cm2/Vs respectively. This study shows promise for scaled up fabrication of graphene based nanoelectronic devices.Comment: 8 pages, 6 figure

Space charge limited conduction with exponential trap distribution in reduced graphene oxide sheets

We elucidate on the low mobility and charge traps of the chemically reduced graphene oxide (RGO) sheets by measuring and analyzing temperature dependent current-voltage characteristics. The RGO sheets were assembled between source and drain electrodes via dielectrophoresis. At low bias voltage the conduction is Ohmic while at high bias voltage and low temperatures the conduction becomes space charge limited with an exponential distribution of traps. We estimate an average trap density of 1.75x10^16 cm^-3. Quantitative information about charge traps will help develop optimization strategies of passivating defects in order to fabricate high quality solution processed graphene devices.Comment: 6 pages, 3 figures, 1 tabl

A randomised controlled trial of suture materials used for caesarean section skin closure: Do wound infection rates differ?

Objective. The aim of this study was to determine wound complication rates following the use of suture materials and staples for skin closure at caesarean section (CS). Study design: A randomised, controlled, prospective study was undertaken.Results. A total of 1 100 women was assigned randomly into 3 groups: polyglycolic acid (PGA) suture group (N=361), skin staple (SS) group (N=373) and nylon suture group (N=366). The overall wound infection rate was 7%. There was no difference in respect of number of patients, age, parity and gestation between the study groups. Those who had nylon sutures as opposed to PGA sutures were 9.5 times more likely to experience wound infection (p=0.055). Women who had SS were at 6.93 times higher risk of wound infection than those who had PGA sutures (p=0.014). Other factors influencing wound infection rates included: rupture of membranes >12 hours were 13.7 times (95% confidence interval (CI) 3.9 - 47.9, p <0.0001) more likely to have wound infection than those with rupture of membranes <12 hours. For every 1-minute increase of surgery duration, the risk of infection increased 1.094 times (95% CI 1.046 - 1.145; p <0.0001). HIV-infected women were 53.4% less likely to develop wound infection than their uninfected counterparts (odds ratio 0.466, 95% CI 0.238 - 0.913; p =0.026). As the time period of observation increased from baseline to day 3 and from day 3 to day 10, wound infection risk increased by 35 times (95% CI 8.155 - 150.868; p <0.001).Conclusion. The use of SS for CS wound closure is associated with a significantly greater risk of wound infections. SS for wound closure at CS is not recommended for use in South African district hospitals.S Afr Med J 2012;102(6):374-376

A Passive Microfluidic Valve Using Superhydrophobic/Hydrophilic Nanostructures For Lab-On-A-Chip (Loc) Systems

This paper describes a passive microfluidic valve, which has an integrated superhydrophobic surface in one of the channels to selectively inhibit the flow of water based reagents and pass aqueous solutions containing surfactants. The microchannels were fabricated by standard photolithography and wet etching techniques. The superhydrophobic polymer patch was fabricated using the layer-by-layer (LBL) deposition technique, in which multiple layers of polyelectrolytes were coated on a channel wall followed by silica nanoparticle treatment. The channels were sealed with a polydimethylsiloxane (PDMS) slab by treating under oxygen plasma. The fabricated microfluidic valve was tested with liquids flowing in the microchannels under capillary action. It is shown that the valve selectively regulates the flow of test samples. The water sample stops at the front of superhydrophobic patch and the 2-isopropanol flows through the channels without any resistance. ©2007 IEEE

A Passive Microfluidic Valve using Superhydrophobic/Hydrophilic Nanostructures for Lab-on-A-Chip (LOC) Systems

This paper describes a passive microfluidic valve, which has an integrated superhydrophobic surface in one of the channels to selectively inhibit the flow of water based reagents and pass aqueous solutions containing surfactants. The microchannels were fabricated by standard photolithography and wet etching techniques. The superhydrophobic polymer patch was fabricated using the layer-by-layer (LBL) deposition technique, in which multiple layers of polyelectrolytes were coated on a channel wall followed by silica nanoparticle treatment. The channels were sealed with a polydimethylsiloxane (PDMS) slab by treating under oxygen plasma. The fabricated microfluidic valve was tested with liquids flowing in the microchannels under capillary action. It is shown that the valve selectively regulates the flow of test samples. The water sample stops at the front of superhydrophobic patch and the 2-isopropanol flows through the channels without any resistance. ©2007 IEEE

Microfluidic Valves Based On Superhydrophobic Nanostructures And Switchable Thermosensitive Surface For Lab-On-A-Chip (Loc) Systems

This paper describes a novel valve concept using a nanostructured functional polymer surface. To prove the concept, two fully integrated microfluidic valves, one with a superhydrophobic polymer surface and the other with a switchable, thermosensitive polymer surface have been fabricated and tested. The passive valve with the superhydrophobic polymer surface selectively inhibits the flow of water-based reagents and passes aqueous solutions containing surfactants. In case of the thermosensitive valve, the switchable polymer surface becomes hydrophobic when heated to temperatures exceeding 65 °C, thus inhibiting the flow of water and becomes hydrophilic at room temperature, thus allowing the flow of water. The microchannels are fabricated by standard photolithography and wet etching techniques. The polymer surface for both the valves is fabricated using the layer-by-layer (LBL) deposition technique, in which multiple layers of polyelectrolytes are coated on a channel wall followed by silica nanoparticle treatment. For the thermosensitive valve, the polymer surface is further coated with the thermosensitive polymer poly(N-isopropylacrylamide) (PNIPAAm). The fabricated microfluidic valve was tested with liquids flowing in the microchannels under capillary action. It is shown that the valve selectively regulates the flow of test samples. © 2007 Elsevier B.V. All rights reserved

High Yield Fabrication Of Chemically Reduced Graphene Oxide Field Effect Transistors By Dielectrophoresis

We demonstrate high yield fabrication of field effect transistors (FET) using chemically reduced graphene oxide (RGO) sheets. The RGO sheets suspended in water were assembled between prefabricated gold source and drain electrodes using ac dielectrophoresis. With the application of a backgate voltage, 60% of the devices showed p-type FET behavior, while the remaining 40% showed ambipolar behavior. After mild thermal annealing at 200 °C, all ambipolar RGO FET remained ambipolar with increased hole and electron mobility, while 60% of the p-type RGO devices were transformed to ambipolar. The maximum hole and electron mobilities of the devices were 4.0 and 1.5cm2V-1s -1 respectively. High yield assembly of chemically derived RGO FET will have significant impact in scaled up fabrication of graphene based nanoelectronic devices. © 2010 IOP Publishing Ltd

A randomised controlled trial on suture materials for skin closure at caesarean section: Do wound infection rates differ?

Objective.The aim of this study was to determine wound complication rates following the use of suture materials and staples for skin closure at caesarean section (CS). Study design: A randomised, controlled, prospective study was undertaken. Results. A total of 1 100 women was assigned randomly into 3 groups: polyglycolic acid (PGA) suture group (N=361), skin staple (SS) group (N=373) and nylon suture group (N=366). The overall wound infection rate was 7%. There was no difference in respect of number of patients, age, parity and gestation between the study groups. Those who had nylon sutures as opposed to PGA sutures were 9.5 times more likely to experience wound infection (p=0.055). Women who had SS were at 6.93 times higher risk of wound infection than those who had PGA sutures (p=0.014). Other factors influencing wound infection rates included: rupture of membranes >12 hours were 13.7 times (95% confidence interval (CI) 3.9 - 47.9,

Regulation of T cell differentiation and alloimmunity by the cyclin-dependent kinase inhibitor p18ink4c.

Cellular proliferation in response to mitogenic stimuli is negatively regulated by the Cip/Kip and the Ink4 families of cyclin-dependent kinase (CDK) inhibitors. Several of these proteins are elevated in anergic T cells, suggesting a potential role in the induction or maintenance of tolerance. Our previous studies showed that p27kip1 is required for the induction of T cell anergy and transplantation tolerance by costimulatory blockade, but a role for Ink4 proteins in these processes has not been established. Here we show that CD4+ T cells from mice genetically deficient for p18ink4c divide more rapidly than wild-type cells in response to antigenic, costimulatory and growth factor signals. However, this gain of proliferative function was accompanied by a moderate increase in the rate of cell death, and was accompanied by an overall defect in the generation of alloreactive IFNγ-producing effector cells. Consistent with this, p18ink4c-deficient T cells were unable to induce graft-vs-host disease in vivo, and p18ink4c deficiency cooperated with costimulatory blockade to significantly increase the survival of fully mismatched allografts in a cardiac transplantation model. While both p18ink4c and p27kip1 act to restrict T cell proliferation, p18ink4c exerts an opposite effect from p27kip1 on alloimmunity and organ transplant rejection, most likely by sustaining T cell survival and the development of effector function. Our studies point to additional important links between the cell cycle machinery and the processes of T cell differentiation, survival and tolerance