We present for the first time TEM cross-section studies of Au nanowires fabricated with nanostencil membranes. Au metallic nanowires from 100 to 20 nm in width are fabricated on metallic, semiconducting and insulating substrates. The observed profiles require consideration of wetting for a satisfactory understanding. This length scale is easily accessible by simulations, thereby making it possible to model the cross-section profiles. In addition, the fabrication capabilities of the nanostencil technique are thus critically evaluated for the fabrication of metallic nanowires on different substrates up to 20 nm linewidths. We find a clear separation between spreading-dominated and wetting-dominated behaviour. Substrates such as HOPG and mica aid spreading. The 1:1 geometrical reproduction rule is well respected in the wetting case down to the 20 nm limit, before the clogging of the mask on all other substrates.
A new methodology for detecting the microbiological state of a wound dressing in terms of its colonization with pathogenic bacteria such as Staphylococcus aureus or Pseudomonas aeruginosa has been developed. Here we report how stabilized lipid vesicles containing self-quenched carboxyfluorescein dye are sensitive to lysis only by toxins/virulence factors from P. aeruginosa and S. aureus but not by a non-toxic Escherichia coli species. The development of the stabilized vesicles is discussed and their response to detergent (triton), bacterial toxin (α-hemolysin) and lipases (phospholipase A(2)). Finally, fabrics with stabilized vesicles attached via plasma deposited maleic anhydride coupling are shown visibly responding to S. aureus (MSSA 476) and P. aeruginosa (PAO1) but not E. coli DH5α in a prototype dressing.
Pathogenic bacteria secrete various virulence factors that can directly interact with the outer lipid bilayer membrane of eukaryotic cells, inducing cell death by apoptosis or necrosis. Such virulence factors account for much of the toxic action associated with bacterial infection; therefore the detection of such proteins could provide a methodology for sensing / detection of pathogenic bacteria in, for example, food or human tissue. Detection and identification of pathogenic bacteria by conventional methods such as plating and counting in laboratory is expensive and time consuming. With growing concerns over emergence and re-emergence of pathogenic bacteria with high resistant to current antibiotics, there is a potential need for effective detection of pathogenic toxins in-vitro. This paper presents the application of tethered bilayer lipid membrane (TBLM) as a sensing platform for the detection of the clinically relevant pathogenic bacterial, Staphylococcus aureus MSSA 476 and Pseudomonas aeruginosa PAO1 via their secreted virulence factors, using electrochemical impedance spectroscopy (EIS). A non-pathogenic strain of bacteria, E. coli DH5α was used as a control. A clear difference in the impedance of the TBLM for the pathogenic vs. non-pathogenic species was observed.
Pathogenic bacteria secrete various virulence factors, including toxins, lipases and proteases that allow them to infect, breakdown and colonize host tissue. Among various modes of action that the pathogenic bacteria use to damage the host, pore formation (by pore forming toxins (PFTs)) and lipid hydrolysis (by phospholipases) modes are common in damaging the eukaryotic cell membrane. PFTs in their monomeric form are extracellular diffusible and able to form hydrophilic pores in cell membrane while phospholipases cleaves and hydrolyzes the ester bonds of most phospholipids in cell membrane. Both modes of action cause uncontrolled permeation of ions and molecules across cell membrane, leading to cell death by apoptosis or necrosis. In this work, the toxins secreted by two clinically important human pathogens, methicillin susceptible Staphylococcus aureus (MSSA476) and Pseudomonas aeruginosa (PAO1) were studied via their interaction with a planar tethered bilayer lipid membrane (pTBLM) using surface plasmon resonance spectroscopy (SPR) and electrochemical impedance spectroscopy (EIS). Detection and discrimination is based on lipid-loss (lipid hydrolysis by phospholipases) or non lipid-loss (pore formation by PFTs) from pTBLM upon interaction with supernatant of pathogenic bacteria. Using EIS and SPR, it is demonstrated that major toxins of S. auerus are PFTs while most of toxin associated with P. aeruginosa are more lipid damaging lipolytic enzymes. Such a format might have future utility as a simple assay for measuring the presence membrane lytic virulence factors in clinical samples.
In a planar configuration, multiple electrical connections to a single molecule require an atomic scale precision of the wiring and an atomically flat supporting surface. Current nanofabrication techniques cannot achieve this on the same surface of a wafer. A double sided interconnection process flow adopted from sensor technology is presented using silicon on insulator substrates. The top part of the wafer is exclusively reserved for atomic scale interconnect and constructions. The back side is reserved for all the other interconnection steps. To ensure the passage between the back and the top side of the wafer, nanoscale vias are fabricated through the full thickness of the wafer. The top end of each via is boron and phosphorus doped, and the interconnection leakage current-voltage characteristics are measured. At low voltage and for top inter-via distances in the 30–50 nm range, a high gigaohm range resistance is obtained.
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