Beckman Institute Graduate Student Seminar Scheduled for November 14

The next Beckman Institute Graduate Student seminar will be held on Wednesday, November 14 at Noon in Room 1005 at the Beckman Institute. The following presentations will be featured: "DNA Ligation for Permanent Colloidal Assembly" by Margaret Shyr; "Functional connectivity in the aging brain" by Michelle Webb Voss; and "Carbon Nanotube for High-Performance Flexible Electronics" by Qing Cao. The hour-long seminar is open to the public and a pizza lunch will be served.

DNA Ligation for Permanent Colloidal Assembly
Margaret Shyr

Self-assembly methods for creating colloidal crystals are robust methods for forming a limited number of well-ordered crystal structures. DNA-directed colloidal assembly has been pursued as a means to form colloidal crystal structures that are inaccessible by conventional methods. We report that another DNA functionality, DNA ligation, can be employed to selectively ligate assembled colloidal structures while disregarding unhybridized ssDNA. ssDNA functionalized colloids and similarly modified glass substrates were hybridized using a linker-sequence and ligated using DNA ligase to yield sequence-specific permanent fixation of assembled colloids. Furthermore, by combining conventional colloidal self-assembly techniques with DNA-modified colloids, we deposited multilayers of colloids, ligated the first layer to the DNA-modified surface, and rinsed away the non-ligated layers. Not only were the remaining ligated monolayers well ordered; but also since the non-ligated DNA was able to hybridize and ligate to a subsequent layer, simply cycling the process assembled layer-by-layer hcp structures. Furthermore, by simply varying the diameter of the colloids, non-FCC crystals were assembled; all structures were imaged using confocal and fluorescence microscopy.

Functional connectivity in the aging brain
Michelle Webb Voss

Normal aging is associated with a decline in cognitive functions, such as processing speed, selective attention, and executive-control skills such as inhibition, planning, and working memory. Functional brain imaging studies have also revealed that the aging brain is characterized by increased variability in brain activation patterns, that are often hard to resolve in unified theories of cognitive aging. However, recent research has started to characterize cognitively relevant resting state networks (RSNs) in the brain that may help to uncover fundamental changes in the brain with increasing age that contribute to age-related cognitive decline. In this talk I present new research that I am working on to identify and characterize RSNs in the aging brain. Previous research in our lab has also shown that increased aerobic fitness is structurally and functionally neuroprotective with increasing age. To this end, I will present new findings that suggest aerobic fitness moderates functional connectivity in the aging brain.

Carbon Nanotube for High-Performance Flexible Electronics
Qing Cao

Random networks or aligned arrays of single-walled carbon nanotubes (SWNTs) can form effective thin films for flexible electronics. They can serve as either conductive or semiconducting materials in these systems and exhibit several attractive properties, including very high carrier mobilities, extreme levels of mechanical bendability and excellent optical transparency. They are compatible with low cost printing-like fabrication processes and flexible plastic substrates. Here we report the latest achievements made in this emerging field by our group. In particular, we demonstrated device mobilities above 1000 cm2V-1s-1 in our SWNT thin-film transistors (TFTs) with cut-off frequency beyond 10GHz through developing techniques to grow aligned arrays of nanotubes. At the same time, the operating gate voltages have decreased from ~20 V to ~1 V and, in related work, the hysteresis has been reduced to values that are nearly negligible. Not only p-channel but also and n-channel devices have been achieved by use of simple polymer coating strategies. Unusual transparent and/or stretchable TFTs based on SWNT films have been also demonstrated in some prototype devices. Complex digital circuits composed of nearly 100 SWNT TFTs have been successfully demonstrated, paved the road for nanotube flexible electronics to go from science to gadgets.