Surface functionalization of crystalline silicon substrates

In this work, various chemical and electrochemical methods were demonstrated to attach application-specific organic monolayers to crystalline silicon substrates. In one study, alkyl monolayers were anodically electrografted or thermally grafted onto planar (100) silicon substrates using Grignard precursors. The results show electrografted methyl monolayers provide a stable Si-C termination, resisting oxidation on (100) surfaces for approximately 55 days in air. The alkyl termination could provide a potential alternative to defective native oxides and kinetically unstable hydride surfaces. A mechanism involving two electron transfers per grafting event was established for both the thermal and electrochemical routes. In another study, unsaturated organic functional groups (phenylacetylene, 5-hexynoic acid) were cathodically electrografted onto planar (100) silicon substrates. Although cathodic grafting mechanism is considerably different, its voltammetric behavior (hysteresis, onset potential shifts) appears similar to anodic grafting process. Experimental results show both anodic and cathodic grafting methods may be applied to pattern the silicon surfaces in situ. Dielectric templates such as polystyrene microspheres or polydimethylsiloxane stamps were used to obtain high throughput, nanoscale monolayer patterns on silicon surfaces. The patterned monolayers may be further used to immobilize biological enzymes via 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide (EDC) chemistry or to direct selective copper electrodeposition or etching on silicon. Established grafting mechanisms were applied to functionalize nanoscale silicon anodes in lithium batteries to improve capacity retention with charge/discharge cycling. Silicon anodes present a safe, high-capacity alternative to conventional carbonaceous anodes; however, a significant capacity loss (\u3e20% initial value) is observed within the first few cycles, primarily due to 300% volume expansion upon lithiation. Silicon nanowires with atleast one dimension \u3c300 nm may withstand the volume expansion effects but may not completely eliminate the capacity fade. This residual fade is mainly a result of protective solid electrolyte interphase (SEI) layer formed on the anode surface due to electrolyte dissociation. Various ex situ and in situ functionalized silicon surfaces were investigated to establish engineered silicon-SEI interface with improved chemical, mechanical and electrical aspects. The work shows silicon lithiation is a function of surface chemistry and in situ methyl siloxane functionalization offers improved capacity retention with nanoscale silicon anodes in lithium batteries

Electrochemical patterning of organic monolayers on silicon

Organic monolayers may be grafted onto silicon surfaces using an in situ electrochemical patterning method. In this technique, dielectric templates such as polystyrene spheres (ε=2.5) or poly(dimethylsiloxane) stamps (ε=2.3-2.8) are placed in close proximity to, or in direct contact with, silicon electrodes while a potential is applied to drive electrografting reactions. In this work, the authors describe methyl monolayer patterns created in anodic processes and phenylacetylene monolayer patterns created in cathodic processes. Both anodic and cathodic processes show similar chronoamperometric behavior, suggesting silicon passivation associated with the formation of monolayers. Atomic force microscopy shows the sizes, geometries, and thickness of patterned films. Comparison of experimental results with electric field simulations also shows that solution resistance controls the feature sizes, resulting from electrografting with proximal dielectric templates. Similarly, electrochemical impedance spectroscopy shows that the films are densely packed with relatively low levels of defects. The versatile technique is further demonstrated as a monolayer resist for patterned electrodeposition of copper on silicon. © 2010 The Electrochemical Society

Substrate recruitment mechanism by gram-negative type III, IV, and VI bacterial injectisomes

Bacteria use a wide arsenal of macromolecular substrates (DNA and proteins) to interact with or infect prokaryotic and eukaryotic cells. To do so, they utilize substrate-injecting secretion systems or injectisomes. However, prior to secretion, substrates must be recruited to specialized recruitment platforms and then handed over to the secretion apparatus for secretion. In this review, we provide an update on recent advances in substrate recruitment and delivery by gram-negative bacterial recruitment platforms associated with Type III, IV, and VI secretion systems

Biochemical characterization of MmgB, a gene encoding a 3-Hydroxybutyryl-CoA dehydrogenase from bacillus subtilis 168 and genetic evidence for the methylcitric acid cycle in bacillus subtilis 168

Bacillus subtilis is an industrially important organism because of its ability to produce enzymes and antibiotics on a commercial scale. It is considered the Gram positive counterpart of E. coli in terms of its genetic and molecular biological accessibility. Also, it is a model organism for the study of sporulation, an example of prokaryotic cellular differentiation. Sporulation involves several groups of genes that encode apparent metabolic pathways, many of which remain uncharacterized at the biochemical level. The mmg (mother cell metabolic gene) operon in B. subtilis strain 168 is one of these groups, and is transcribed only during an early stage of sporulation. This operon contains mmgABC, which are similar to genes from fatty acid metabolism, and mmgDE and yqiQ, which encode homologs of enzymes involved in the 2-methylcitric acid cycle. The focus of this work will be on the biochemical characterization of the mmgB protein, which is similar by sequence to 3-hydroxyacyl-coenzyme A (CoA) dehydrogenase from a wide variety of organisms. So far, we successfully cloned and overexpressed mmgB, and purified the protein at a yield of 4.0 mg/liter of culture. A spectrophotometric assay and mass spectrometry showed that this enzyme indeed possesses 3-hydroxybutyryl-CoA dehydrogenase activity (E.C. 1.1.1.157) for the production of acetoacetyl-CoA. This oxidation specifically requires NADP+, and has an optimal pH of 9.8. We will describe these results including the steady-state kinetics that the enzyme follows. As previously said, the downstream 3 ORF's of the mmg operon - mmgD, mmgE and yqiQ are proposed to encode for the methylcitric acid cycle. Also, as a part of a master's thesis, it has been shown by the Reddick lab that mmgD encodes for a citrate/methylcitrate synthase with a substrate preference for propionyl-CoA over acetyl-CoA. This fact encouraged us even more with reference to the involvement of the mmg operon in the methylcitric acid cycle, a pathway for propionate metabolism. So, our goal was to create conditional knockout mutants of the mmg operon and study the growth characteristics of the organism by feeding studies using propionate as sole carbon source. Eventually, we would also want to perform some NMR analysis of the cultures of the mutants for the intermediates of methylcitric acid cycle/propionate metabolism

Substrate recruitment mechanism by gram-negative type III, IV, and VI bacterial injectisomes

Bacteria use a wide arsenal of macromolecular substrates (DNA and proteins) to interact with or infect prokaryotic and eukaryotic cells. To do so, they utilize substrate-injecting secretion systems or injectisomes. However, prior to secretion, substrates must be recruited to specialized recruitment platforms and then handed over to the secretion apparatus for secretion. In this review, we provide an update on recent advances in substrate recruitment and delivery by gram-negative bacterial recruitment platforms associated with Type III, IV, and VI secretion systems

Orientation-independent bubble trap with internal partition for robust operation of microfluidic systems

A new monolithic bubble trap has been developed with a unique, orientation-independent design. The bubble trap has a spherical cavity and a central partition with internal passages that eliminate air bubbles effectively for extended periods of time. Flow testing was performed in a closed-loop microfluidic system to demonstrate effectiveness and robustness of the bubble trap. Flow rate was continually monitored on a stationary benchtop and also in simulated microgravity conditions on a 3-D random positioning machine. Data collected from flow sensors placed fore and aft of the bubble trap confirmed that randomly occurring bubbles were effectively eliminated by the trap throughout 24 hour closed-loop perfusion tests. To highlight the orientation-independent benefit of the bubble trap in a specific application of interest, continuous-flow experiments were conducted using human umbilical vein endothelial cells in a closed-loop microfluidic system. The bubble trap successfully protected the integrity of confluent layers that otherwise suffered from cell detachment without the trap. Image analysis showed that random orientation reduced directional alignment of cell nuclei, relative to baseline experiments performed under normal gravity

Prevalence, clinical investigation, and management of gallbladder disease in Rett syndrome

AIM: This study determined the prevalence of cholelithiasis and/or cholecystectomy in Rett syndrome, described gallbladder function in a clinical cohort, and identified recommendations for assessment and management of gallbladder disease. METHOD The incidence of cholelithiasis/cholecystectomy was estimated from data describing 270 and 681 individuals with a pathogenic MECP2 mutation in the Australian Rett Syndrome Database and the International Rett Syndrome Phenotype Database respectively. Gallbladder function in 25 females (mean age 16y 5mo, SD 20y 7mo, range 3y 5mo–47y 10mo) with Rett syndrome (RTT) was evaluated with clinical assessment and ultrasound of the gallbladder. The Delphi technique was used to develop assessment and treatment recommendations. RESULTS: The incidence rate for cholelithiasis and/or cholecystectomy was 2.3 (95% confidence interval [CI] 1.1–4.2) and 1.8 (95% CI 1.0–3.0) per 1000 person-years in the Australian and International Databases respectively. The mean contractility index of the gallbladder for the clinical sample was 46.5% (SD 38.3%), smaller than for healthy individuals but similar to children with Down syndrome, despite no clinical symptoms. After excluding gastroesophageal reflux, gallbladder disease should be considered as a cause of abdominal pain in RTT and cholecystectomy recommended if symptomatic. INTERPRETATION: Gallbladder disease is relatively common in RTT and should be considered in the differential diagnosis of abdominal pain in RTT