Integrated Calendar

Halide (hybrid) perovskites (HaP) have emerged as a new class of semiconductors that truly encompass all the desired physical properties for building optoelectronic and quantum devices such as large tunable band-gaps, large absorption coefficients, long diffusion lengths, low effective mass, good mobility and long radiative lifetimes. In addition, HaPs are solution processed or low-temperature vapor grown semiconductors and are made from earth abundant materials thus making them technologically relevant in terms of cost/performance. As a result, proof-of-concept high efficiency optoelectronic devices such as photovoltaics and LEDs have been fabricated. In fact, photovoltaic efficiencies have sky rocketed to 23% merely in the past five years and are nearly on-par with mono-crystalline Si based solar cells. Such unprecedented progress has attracted tremendous interest among researchers to investigate the structure-function relationship and understand as to what makes Halide hybrid perovskites special?
In my talk, I will attempt to answer some of the key questions and in doing so share the results from our work on HaPs over the past four years in understanding structure induced properties of HaPs. I will also highlight fundamental bottlenecks that exist going forward which present opportunities to create platforms to understand the interplay between light, fields and structure on the properties of perovskite-based materials.

Protein design—i.e., the construction of entirely new protein sequences that fold into prescribed structures—has come of age: it is possible now to generate a wide variety stable protein folds from scratch using rational and/or computational approaches. A challenge for the field is to move from what have been largely in vitro exercises to protein design in living cells and, in so doing, to augment biology. This talk will illustrate what is currently possible in this nascent field using de novo -helical coiled-coil peptides as building blocks.1

Coiled coils are bundles of 2 or more  helices that wrap around each other to form rope-like structures. They are one of the dominant structures that direct natural protein-protein interactions. Our understanding of coiled coils provides a strong basis for building new proteins from the bottom up. The first part of this talk will survey this understanding,1 our design methods,2,3 and our current “toolkit” of de novo coiled coils.4-6

Next, I will describe how the toolkit can be used to direct protein-protein interactions and build complex protein assemblies in bacterial cells. First, in collaboration with the Savery lab (Bristol), we have used homo- and hetero-oligomeric coiled coils as modules in engineered and de novo transcriptional activators and repressors.7 Secondly, with the Warren (Kent) and the Verkade (Bristol) labs, we have engineered hybrids of a de novo heterodimer and a natural component of bacterial microcompartments to form a “cytoscaffold” that permeates E. coli cells.8 This can be used to support the co-localisation of functional enzymes.

Due to the immense complexity of the human brain, the study of its development, function, and dysfunction during health and disease has proven to be challenging. The advent of patient-derived human induced pluripotent stem cells, and subsequently their self-organization into three-dimensional (3D) brain organoids, which mimics the complexity of the brain's architecture and function, offers an unprecedented opportunity to model human brain development and disease in new ways. However, there is still a pressing need to develop new technologies that recapitulate the long-term developmental trajectories and the complex in vivo cellular environment of the brain. To address this need, we have developed a human brain organoid-based approach to generate a chimeric human/animal brain system that facilitates long-term ana! tomical integration, differentiation, and vascularization in vivo. We also demonstrated the development of functional neuronal networks within the brain organoid and synaptic-cross interaction between the organoid axonal projections and the host brain. This approach set the stage for investigating human brain development and mental disorders in vivo, and run therapeutic studies under physiological conditions.

The trion, a three-body charge-exciton bound state, offers unique opportunities to simultaneously manipulate charge, spin and excitation in one-dimensional single-walled carbon nanotubes (SWNTs) at room temperature. Effective exploitation of trion quasiparticles requires fundamental insight into their creation and decay dynamics. Such knowledge, however, remains elusive for SWNT trion states, due to the electronic and morphological heterogeneity of commonly interrogated SWNT samples, and the fact that transient spectroscopic signals uniquely associated with the trion state have not been identified. Here length-sorted SWNTs and precisely controlled charge carrier-doping densities are used to determine trion dynamics using femtosecond pump-probe spectroscopy. Identification of the trion transient absorptive hallmark enables us to demonstrate that trions (i) derive from a precursor excitonic state, (ii) are produced via migration of excitons to stationary hole-polaron sites, and (iii) decay in a first-order manner. Importantly, under appropriate carrier-doping densities, exciton-to-trion conversion in SWNTs can approach 100% at ambient temperature. We further show that ultrafast pump-probe spectroscopy, coupled with these fundamental insights into trion formation and decay dynamics, enables a straightforward approach for quantitatively evaluating the extent of optically-driven free carrier generation (FCG) in SWNTs: this work provides fundamental new insights into how quantum yields for optically-driven FCG [Φ(Enn → h+ + e−)] in SWNTs may be modulated as functions of the optical excitation energy and medium dielectric strength. Collectively, these findings open up new possibilities for exploiting trions in SWNT optoelectronics, ranging from photovoltaics, photodetectors, to spintronics.

In this talk, I will introduce the Nature Communications journal, the editorial office in Shanghai, the editorial process and insiders’ view on the Nature Communications.


Bo joined Nature Communications in March 2017. Following his undergraduate studies in Zhejiang University, China, he obtained his PhD in Physics at National University of Singapore. He then carried out his postdoctoral research at Graphene Research Center in Singapore and University of Washington. He currently handles manuscripts on solar cells and halide perovskite photophysics. Bo is based in the Shanghai office.

4H-SiC epitaxial layers were irradiated using various radioactive sources and particle accelerators. The electronic properties of induced defects were characterized by means of deep-level transient spectroscopy (DLTS) and Laplace DLTS. This presentation is a review of various observations due to processing various particles used in irradiation of 4H-SiC. From the results it was evident that the same defects were induced by various radiation sources. Irradiation induced the acceptor level of the Z1 center and the donor level of the Z2 center. The concentration of the native defects, which originate from impurities encountered in the growth process increased. DLTS spectra observed after irradiation were exhibited sitting on skewed baselines which in some instances inhibited accurate Laplace-DLTS resolution.

Hsp90 plays a central role in cell homeostasis by assisting folding and maturation of many client proteins. In order to perform this chaperoning activity Hsp90 hydrolyzes ATP, which requires Mg(II) as cofactor and the hydrolysis is coupled to large global conformational changes. Hsp90 is homo-dimeric with each monomer consisting of three consecutive domains (CTD, MD, NTD). The ATPase site is found in each of the two NTDs, while the CTDs constitute the dimerization site. X-ray crystallography and FRET have provided insights on the conformational cycle of Hsp90 which involves transition from a nucleotide-free ‘open’ to a nucleotide-bound ‘closed’ conformation by dimerization of the NTDs. However, there are still open questions on whether the chaperone shifts global conformation as a consequence of hydrolysis.
Here, we investigate the ATPase site and the concomitant conformational changes at various nucleotide-bound states (pre-hydrolysis, intermediate high energy and post- hydrolysis states) in yeast Hsp90 using EPR techniques. To do so, we substituted the Mg(II) cofactor with paramagnetic Mn(II) and performed hyperfine and pulsed dipolar EPR experiments, to probe short and long range interactions, respectively. Specifically, we tracked ATP hydrolysis by exploring the Mn(II) coordination by the nucleotide phosphates using 31P electron nuclear double resonance (ENDOR) spectroscopy. The interaction of the Mn(II) with protein residues in the different hydrolysis states was investigated by 14/15N ELDOR-detected nuclear magnetic resonance (EDNMR). Last, we measured the distance between the two Mn(II) cofactors in each of the monomers using double electron–electron resonance (DEER/PELDOR) spectroscopy. Here, we measured a well-defined Mn(II)-Mn(II) distance of 4.3 nm in the pre-hydrolysis state, which changes both in width and mean distance in the post-hydrolysis state providing experimental evidence to the existence of two different ‘closed’ conformations for the ATP and ADP bound states. Within our approach one can probe both local and global interactions from a single sample via exploitation of intrinsic sites (here Mg(II)->Mn(II)) that can potentially yield new structural insights previously challenging to observe with FRET and EPR using site-specific spin labeling.