Formation of Free-Standing Inverse Opals with Gradient Pores.

We demonstrate the fabrication of free-standing inverse opals with gradient pores via a combination of electrophoresis and electroplating techniques. Our processing scheme starts with the preparation of multilayer colloidal crystals by conducting sequential electrophoresis with polystyrene (PS) microspheres in different sizes (300, 600, and 1000 nm). The critical factors affecting the stacking of individual colloidal crystals are discussed and relevant electrophoresis parameters are identified so the larger PS microspheres are assembled successively atop of smaller ones in an orderly manner. In total, we construct multilayer colloidal crystals with vertical stacking of microspheres in 300/600, 300/1000, and 300/600/1000 nm sequences. The inverse opals with gradient pores are produced by galvanostatic plating of Ni, followed by the selective removal of colloidal template. Images from scanning electron microscopy exhibit ideal multilayer close-packed structures with well-defined boundaries among different layers. Results from porometer analysis reveal the size of bottlenecks consistent with those of interconnected pore channels from inverse opals of smallest PS microspheres. Mechanical properties determined by nanoindentation tests indicate significant improvements for multilayer inverse opals as compared to those of conventional single-layer inverse opals.

Seasonal Distribution and Container Preference Ratio of the Dengue Fever Vector (Aedes aegypti, Diptera: Culicidae) in Rawalpindi, Pakistan.

Aedes aegypti (L.) and Aedes albopictus (Skuse) are known vectors of dengue, chikungunya, and other pathogens; however, their ecology and role in virus transmission has not been well studied in Pakistan. Here, we report on an intensive survey of potential breeding sites of Ae. aegypti in Rawalpindi, Punjab Province, Pakistan. The study continued for 11 mo and was divided into three seasons: January to June (pre-monsoon), July to September (monsoon), and October-November (post-monsoon). Larval mosquitoes were collected from all wet containers present in and around the houses. Altogether 5,570,418, 2,930,508, and 1,507,111 water-filled containers were examined during each season, of which 2,703, 8,843, and 3,439 were found positive for Ae. aegypti larvae or pupae, yielding Breteau indices of 0.46, 2.92, and 1.99%, respectively. Among 14 container types examined, the breeding preference ratio during all seasons was highest for roof-top water tanks and room evaporative coolers, followed by discarded tires and urban trash. The study concluded that increased urbanization, insufficient water supply and inefficient removal of urban trash resulted in increased numbers of nonbiodegradable containers around human dwellings, thereby creating ideal breeding habitats for Ae. aegypti. Measures such as integrated vector management, minimization of the breeding potential of Ae. aegypti by water management, proper disposal of discarded tires and urban trash, and health education were recommended for control of Ae. aegypti.

Structural characterization of colloidal crystals and inverse opals using transmission X-ray microscopy.

A nondestructive tomographic technique was used to determine the crystallographic information of colloidal crystals comprising of polystyrene (PS) microspheres, as well as their silver inverse opals. The properties of the colloidal crystals, such as defects, grain size, grain boundaries, stacking sequence, and grain orientation, were determined using the full field transmission X-ray microscopy (TXM) with a spatial resolution of 50 nm. The PS microspheres (500-750 nm) which underwent a vertical electrophoresis process to form a face-centered cubic (fcc) close-packed structure with an ABCABC packing sequence. In addition, the colloidal crystal exhibited multiple grains, and an orientation variation of 6.1° in the stacking direction between two neighboring grains.