Carrier distributions governed by hole transport in InGaN∕GaN multiple quantum well (MQW) visible light-emitting diodes (LEDs) were investigated using conventional blue LEDs and dual-wavelength blue-green LEDs. It was found that holes were dominantly distributed in the QW close to the p-GaN layer in LEDs with conventional MQW active regions at a current of 20mA. A decrease in the thickness or the height of the quantum-well potential barrier enhanced hole injection into the MQWs located near the n-GaN layer. Reducing the thickness of a GaN quantum-well barrier between the blue QW and green QW did not degrade the electroluminescence (EL) intensity of the LED. In contrast, reducing the potential height of the barrier with material of possibly compromised quality resulted in a degradation of the EL intensity of the LED.

Single-stranded DNA aptamers were generated from a random library to remove arsenic from Vietnamese groundwater. On the basis of significant arsenic contamination levels, three areas in Ha Nam province (Vinh Tru, Bo De, and Hoa Hau) and five areas near the Mekong River Delta (MR1-5) were selected as study areas. The aptamers were in vitro selected using an arsenic aptamer affinity column created by immobilizing arsenic on Affi-gel 10 resin. Quantitative analyses of the aptamer candidates Ars-1 to Ars-8 by surface plasmon resonance (SPR) revealed the Ars-3 aptamer to have the highest affinity to arsenate [(As(V)] and arsenite [As(III)] with a dissociation constant (K(d)) of 4.95 +/- 0.31 and 7.05 +/- 0.91 nM, respectively. The specific affinity interactions of the Ars-3 aptamer to arsenic were verified against other heavy metals. After obtaining successful removal results with a laboratory-prepared aqueous arsenic solution, Ars-3 was applied for removal of any arsenic present in the groundwater samples collected from the studied areas in Vietnam. Field results were also successful: various arsenic concentrations ranging from 28.1 to 739.2 microg/L were completely removed after 5 min of incubation with the arsenic-binding aptamer Ars-3.

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