Category Archives: Publications

Linker-Mediated Self-Assembly Dynamics of Charged Nanoparticles

Guanhua Lin, See Wee Chee, Sanoj Raj, Petr Král, and Utkur Mirsaidov

ACS Nano, 2016, 10 (8), pp 7443–7450. DOI: 10.1021/acsnano.6b01721. Publication Date (Web): August 05, 2016

Using in situ liquid cell transmission electron microscopy (TEM), we visualized a stepwise self-assembly of surfactant-coated and hydrated gold nanoparticles (NPs) into linear chains or branched networks. The NP binding is facilitated by linker molecules, ethylenediammonium, which form hydrogen bonds with surfactant molecules of neighboring NPs. The observed spacing between bound neighboring NPs, ∼15 Å, matches the combined length of two surfactants and one linker molecule. Molecular dynamics simulations reveal that for lower concentrations of linkers, NPs with charged surfactants cannot be fully neutralized by strongly binding divalent linkers, so that NPs carry higher effective charges and tend to form chains, due to poor screening. The highly polar NP surfaces polarize and partly immobilize nearby water molecules, which promotes NPs binding. The presented experimental and theoretical approach allows for detail observation and explanation of self-assembly processes in colloidal nanosystems.

Read online: ACS Nano.

Transcriptional enhancement of Smn levels in motoneurons is crucial for proper axon morphology in zebrafish

by Zoltan Spiro, Angela Koh, Shermaine Tay, Kelvin See, Christoph Winkler

Scientific Reports 6, 2016  (07 June 2016)

An unresolved mystery in the field of spinal muscular atrophy (SMA) is why a reduction of the ubiquitously expressed Smn protein causes defects mostly in motoneurons. We addressed the possibility that this restricted vulnerability stems from elevated Smn expression in motoneurons. To explore this, we established an ex vivo zebrafish culture system of GFP-marked motoneurons to quantitatively measure Smn protein and smn mRNA levels as well as promoter activity in motoneurons versus other cell types. Importantly, we uncovered that Smn levels are elevated in motoneurons by means of transcriptional activation. In addition, we identified the ETS family transcription factor Etv5b to be responsible for increased smn transcription in motoneurons. Moreover, we established that the additional supply of Smn protein in motoneurons is necessary for proper axonogenesis in a cell-autonomous manner. These findings demonstrate the reliance of motoneurons on more Smn, thereby adding a novel piece of evidence for their increased vulnerability under SMA conditions.

Read online: Scientific Reports

Diffraction before destruction

by Chun Hong Yoon, Mikhail V. Yurkov, Evgeny A. Schneidmiller, Liubov Samoylova, Alexey Buzmakov, Zoltan Jurek, Beata Ziaja, Robin Santra, N. Duane Loh, Thomas Tschentscher & Adrian P. Mancuso

Scientific Reports. 6 (2016) 24791. doi: 10.1038/srep24791.

Nanometer-sized biological molecules are difficult to resolve because they are fragile: they come apart when they are imaged with energetic x-rays or electrons. Fortunately, ultra-short x-ray laser pulses billions of times brighter than previous x-ray sources can now illuminate single biomolecules to produce faint but meaningful signals. These signals are then statistically combined to yield structural information. Because these x-ray pulses are so short, they flee from biomolecules before the latter get a chance to move or show damage. This property permits so-called “diffraction before destruction”, where scientists can image unsuspecting and unperturbed nanoscale objects in their native environment.

Hundreds of experimental parameters modify how x-ray free-electron lasers are generated, focused, made to interact with biomolecules, then detected, and analysed. The combinatorial complexity of such imaging experiments is staggering, which makes designing such experiments tricky, tedious and frustratingly uncertain. Dr Duane LOH from the Centre for Bio-imaging Sciences, together with four other groups of scientists from CFEL and the European XFEL (Hamburg, Germany), has created a comprehensive multi-physics framework that realistically simulates for the first time, how specimen damage in single-particle imaging can be mitigated by instrument and algorithm design.

Read online: Scientific Reports.

Read Diffraction before destruction: Scientists in NUS have demonstrated how x-ray lasers could help us image biological macromolecules in water from NUS Faculty of Science.