Semiconductor-Metal Nano-Floret Hybrid Structures by Self-Processing Synthesis

We present a synthetic strategy that takes advantage of the inherent asymmetry exhibited by semiconductor nanowires prepared by Au-catalyzed chemical vapor deposition (CVD). The metal–semiconductor junction is used for activating etch, deposition, and modification steps localized to the tip area using a wet-chemistry approach. The hybrid nanostructures obtained for the coinage metals Cu, Ag, and Au resemble the morphology of grass flowers, termed here Nanofloret hybrid nanostructures consisting of a high aspect ratio SiGe nanowire (NW) with a metallic nanoshell cap. The synthetic method is used to prepare hybrid nanostructures in one step by triggering a programmable cascade of events that is autonomously executed, termed self-processing synthesis. The synthesis progression was monitored by ex situ transmission electron microscopy (TEM), in situ scanning transmission electron microscopy (STEM) and inductively coupled plasma mass spectrometry (ICP-MS) analyses to study the mechanistic reaction details of the various processes taking place during the synthesis. Our results indicate that the synthesis involves distinct processing steps including localized oxide etch, metal deposition, and process termination. Control over the deposition and etching processes is demonstrated by several parameters: (i) etchant concentration (water), (ii) SiGe alloy composition, (iii) reducing agent, (iv) metal redox potential, and (v) addition of surfactants for controlling the deposited metal grain size. The NF structures exhibit broad plasmonic absorption that is utilized for demonstrating surface-enhanced Raman scattering (SERS) of thiophenol monolayer. The new type of nanostructures feature a metallic nanoshell directly coupled to the crystalline semiconductor NW showing broad plasmonic absorption

Photopatterning for probing protein-protein interactions in artificial model systems and live cells

Functional immobilization and lateral organization of proteins into micro- and nanopatterns is an important prerequisite for miniaturizing analytical and biotechnological devices. In this thesis I present novel and versatile approaches for high contrast surface micropatterning of proteins, artificial membranes and live cells based on maleimide photochemistry. The patterning strategy is carried-out on glass substrates exploiting a poly(ethylene glycol) PEG polymer layer as a compatible scaffold. The flexible PEG cushion prevents unspecific proteins attachment and cell adhesion to surfaces. The versatility of this method is demonstrated by means of different orthogonal chemistries using covalent- and affinity- based interactions for protein immobilization. Furthermore, using maleimide based alkyl-thiol chemistry, I utilized the patterning approach for capturing liposomes and proteoliposomes onto surfaces. Formation of fluid patterned polymer-supported membranes demonstrating lateral diffusion of lipids and proteins was confirmed by biophysical assays. A similar approach was used for micropatterning of transmembrane proteins in surface adhered live cells

Binding of interferon reduces the force of unfolding for interferon receptor 1

<div><p>Differential signaling of the type I interferon receptor (IFNAR) has been correlated with the ability of its subunit, IFNAR1, to differentially recognize a large spectrum of different ligands, which involves intricate conformational re-arrangements of multiple interacting domains. To shed light onto the structural determinants governing ligand recognition, we compared the force-induced unfolding of the IFNAR1 ectodomain when bound to interferon and when free, using the atomic force microscope and steered molecular dynamics simulations. Unexpectedly, we find that IFNAR1 is easier to mechanically unfold when bound to interferon than when free. Analysis of the structures indicated that the origin of the reduction in unfolding forces is a conformational change in IFNAR1 induced by ligand binding.</p></div

Coarse-grained MD simulations of IFNAR1-EC and contact changes affected by YNS binding.

<p>(A) Histograms of unfolding forces by domains (SD1 –blue, SD2 –green, SD3 –red), with the top graph representing unfolding of the domain on its own and the bottom graph showing the unfolding of the domain in the presence of YNS. (B). Traces of steered MD of IFNAR1-EC domains on its own (I) or with its ligand (II). I and II each consist of 60 traces with colours as in A. C. Residues that have lost contacts with other residues upon interaction with YNS are coloured in cyan whereas those that have gained contacts are coloured in magenta.</p

Forced unfolding of IFNAR1-EC by AFM.

<p>(A) The C-terminal of IFNAR1-EC immobilized onto a mica surface through a flexible linker and an AFM tip interacting with the protein (B) Traces representative of different families of unfolding curves. (C) I. A scatter plot representing the phase space of the system in the <i>ΔL</i>_<i>C</i> vs. <i>F</i> plane. II. Corresponding contour plot (D) I. Histogram of contour length changes fitted by two Gaussians centred at 16 nm and 36 nm with a p-value < 10⁻⁴. II. The force histogram corresponding to the events in I fitted with Gaussians centred at 40 pN and 90 pN.</p

Influence of IFNα2 binding on IFNAR1 unfolding.

<p>Unfolding of IFNAR1-EC on its own (A and B,) or in the presence of 4 μM WT- IFNα2 (K_D = 1.5 μM, C and D), the high affinity mutant YNS (K_D = 0.03 μM, E and F) and the low affinity mutant NLYY (no measureable binding affinity [<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0175413#pone.0175413.ref046" target="_blank">46</a>], G and H). The influence of the ligands is described either by contour plots (C,E,G) or force histograms (D,F,H) each representing 3–4 experiments.</p