Nanoscale Quantum Dot Arrays

The controlled organization of inorganic materials into multi-dimensional addressable arrays is the foundation for both logic and memory devices, as well as other nonlinear optical and sensing devices. Many of these devices are currently fabricated using lithographic patterning processes that have progressively developed toward greater integration densities and smaller sizes. At submicron scales, however, conventional lithographic processes are approaching their practical and theoretical limits. At scales below 100 nm, lithography becomes prohibitively expensive and time consuming, and more importantly, at these scales quantum effects fundamentally change the properties of devices. While there are strong incentives to develop nanoscale architectures, these developments will require alternate fabrication methods and new insights into the behavior of materials on nanometer scales. Arrays of nanoparticles formed by non-conventional methods are being explored for use as viable alternatives to standard lithographically patterned devices, and individual nanoparticles, also known as quantum dots (QDs), have been shown to behave as isolated device components such as single electron transistors.

Protein-Templated Nanoparticle Arrays,

We form nanoscale ordered arrays of quantum dots using a genetically engineered proteins (called HSP60s) that naturally associate into double-ring structures called chaperonins. Starting with a thermostable recombinant HSP60, and using structural information as a guide, we designed chaperonins that contain chemically reactive sites positioned around either 3 or 9 nm apical pores. These engineered chaperonins crystallize into two-dimensional templates up to 10 microns in diameter and size-selectively bind and organize 1.4, 5 and 10 nm gold quantum dots as well as 4.5 nm CdSe-ZnS semiconductor quantum dots. We have shown that, by combining the self-assembling properties of chaperonins with mutations guided by structural modeling, quantum dots can be manipulated and organized into ordered arrays using chaperonins. We are characterizing the physical properties of these arrays for use in next generation optical and electronic devices.

The effects of microbes on the microstructure of hot spring deposits

Soon after the formation of the Earth, where hot springs where abundant environments and most likely populated by life early on. The poor preservation of microbes living in these harsh environments during geologic time makes it difficult to determine if and by what extent they have been populated. In many cases the geologic record of hot springs only bear inorganic deposits, which lack any direct evidences of life (e.g. biomarkers). In contrast to stromatolites, hot spring deposits in most cases do not indicate the presents of life through macroscopic structures. Therefor, it becomes crucial to investigate the influence of organisms on the microstructure of these deposits.

Cold-water stromatolites as an analog for Martian life

Stromatolites are biologically mediated, sedimentary structures which are internally laminated and generally have dome- or column-like morphologies. They are constructed by photosynthetic microbial communities, mostly composed of cyanobacteria, residing in water covered photozoic areas, such as shore lines or shallow lakes. They develop either through the trapping of fine sediment present in the water and subsequently cemented by biogenic CaCO3, or they are completely generated by the biological precipitation of CaCO3. Some of the oldest fossil records of stromatolites are found in Western Australia (North Pole, Pilbara), and date back to about 3.5 Ga. For the most time of Earth's history, stromatolites are the only macroscopic fossils of life that have been preserved until today. They were the dominating life forms appearing on Earth until the Cambrian explosion, around 0.6 Ga ago. Today the remaining actively growing stromatolites are mostly present in harsh environment, where no or only a few competitors are found (e.g. high salinity lagoons, cold-water lakes). The circumstance where stromatolites reflect the oldest macroscopic fossils of microbial communities on Earth, combined with their capability of thriving in extreme environments, makes them ideal structures to look for on Mars and answering the question of whether life was ever present there. If life ever has existed on Mars, microbial communities comparable to terrestrial stromatolites would have been receded to the last remaining lakes before all liquid surface water has disappeared. These last Martian lakes most likely would have been very cold and perhaps frequently covered by ice. Furthermore, most of the lakes will not have had any water outflow since at the end of the warm eon on Mars, no extant water cycle was present that could have created a follow-through system. They can probably be viewed as the last standing ponds slowly evaporated or seeped into the subsurface. During this last stadium of these cold-water lakes, many substances would have been concentrated,such as CaCO3, making the growth of stromatolites-like structures very possible if life was present. Terrestrial lakes that harbor stromatolites and can be used as model environments for Martian lakes will optimally be located in cold areas, without having an incoming and outflowing river. Such a lake is present in Southern Chile, containing cold-water stromatolites at the shoreline of the lake. My goal will be to perform a general assessment of these stromatolites, investigating their morphology, microbiology, and environmental setting.