Sami Yunus

High-Resolution Imaging of Chemical and Biological Sites on Living Cells Using Peak Force Tapping Atomic Force Microscopy

Currently, there is a growing need for methods that can quantify and map the molecular interactions of biological samples, both with high-force sensitivity and high spatial resolution. Force-volume imaging is a valuable atomic force microscopy (AFM) modality for probing specific sites on biosurfaces. However, the low speed and poor spatial resolution of this method have severely hampered its widespread use in life science research. We use a novel AFM mode (i.e., peak force tapping with chemically functionalized tips) to probe the localization and interactions of chemical and biological sites on living cells at high speed and high resolution (8 min for 1 μm × 1 μm images at 512 pixels × 512 pixels). First, we demonstrate the ability of the method to quantify and image hydrophobic forces on organic surfaces and on microbial pathogens. Next, we detect single sensor proteins on yeast cells, and we unravel their mechanical properties in relation to cellular function. Owing to its key capabilities (quantitative mapping, resolution of a few nanometers, and true correlation with topography), this novel biochemically sensitive imaging technique is a powerful complement to other advanced AFM modes for quantitative, high-resolution bioimaging.

Thickness and Elastic Modulus of Plasma Treated PDMS Silica-like Surface Layer

The adhesion of poly(dimethylsiloxane) (PDMS) rubber is largely improved by oxygen plasma surface treatment. The thickness of the silica-like surface layer is characterized by performing transmission electron microscopy imagery on microtome slices of welded plasma treated surfaces. The specific double layer contrast can be considered as equal to twice the thickness of the silica-like layer. The thickness measurements combined with strain-induced elastic buckling instability analysis gives an estimate of the elastic modulus of the silica-like layer equal to 1.5 GPa.

Stretchable helical gold conductor on silicone rubber microwire

Compliant and stretchable three-dimensional golden tracks are produced by metallization of silicone wires maintained under twisting and stretching constraints. Upon release, the metallic track deforms to a helix presenting a wavy and cracked surface. Wavelet and crack orientations are function of three parameters: the wire radius, the number of imposed rotations divided by the length of the cylinder, and the stretching in its axis direction. Electrical conductivity at rest and under stretching can be optimized by finding the prestraining conditions that provide the best trade off between the maximum amount of surface buckling and a limited amount of cracks

Urea potentiometric enzymatic biosensor based on charged biopolymers and electrodeposited polyaniline

A potentiometric biosensor based on urease was developed for the quantitative determination of urea concentration in aqueous solutions for biomedical applications. The urease was either physisorbed onto an electrodeposited polyaniline film (PANI), or immobilized on a layer-by-layer film (LbL) assembled over the PANI film, that was obtained by the alternate deposition of charged polysaccharides (carboxymethylpullulan (CMP) and chitosan (CHI)). In the latter case, the urease (Urs) enzyme was either physically adsorbed or covalently grafted to the LbL film using carbodiimide coupling reaction. Potentiometric responses of the enzymatic biosensors were measured as a function of the urea concentration in aqueous solutions (from 10(-6) to 10(-1) mol L(-1) urea). Very high sensitivity and short response time were observed for the present biosensor. Moreover, a stability study showed a higher stability over time for the potentiometric response of the sensor with the enzyme-grafted LbL film, testifying for the protective nature of the polysaccharide coating and the interest of covalent grafting.

Precise surface patterning of silk fibroin films by breath figures

Silk produced by the silkworm Bombyx mori has gained a second youth as a sustainable material for high-technology applications. Here, we report a simple and cost-effective fabrication technique which allows the preparation of free-standing micropatterned pure protein films under ambient processing conditions. In this view, we take advantage of the auto organization of polymers in microporous films - the so-called breath figure formation - to create a specific morphology, which is then transferred to silk. The method includes, after the construction of a microcavity array, two to four soft-lithographic steps, depending on the desired surface patterning. Arrays of concave or convex microlenses, as well as packed micrometric bumps ordered in a hexagonal fashion, are possible obtainable architectures. Despite the straightforwardness of the procedures proposed, our method is able to produce, with high precision, transparent and stable silk fibroin films shaped with an ordered superficial pattern, which are attractive for the development of new biocompatible photonic devices.

Nanophase Separation in Polystyrene-Polyfluorene Block Copolymers Thin Films Prepared through the Breath Figure Procedure

The amphiphilic block copolymer formed by a hydrophobic body of polystyrene and a hydrophilic head of poly[9,9-di(2-(2-tetrahydropyranyl-oxy)hexyl)fluorene-alt-9,9-dioctylfluorene] was synthesized, and its solution was used to create thin films with ordered pattern of holes, by means of the breath figure technique. These porous films, after a thermal treatment, were found to show ordered aggregates of the pi-conjugated blocks in the place of the cavities. This is probably due to a preorganization of the two different blocks of the copolymer occurring during the breath figure formation, which is driven by the condensation of water microdroplets on the polymer solution, and to a following phase segregation occurring during the thermal annealing. This approach is a promising tool to be employed for the organization of organic materials at the micro and nanoscale.

Controlled aniline polymerization strategies for polyaniline micro- and nano self-assembling into practical electronic devices.

Electroless polymerization of aniline on platinum is investigated for polyaniline micro- and nanostructuring into practical electronic devices. This type of reaction is adapted to estimate its usefulness in a lithographic process. For practical electronic device fabrication, electroless polymerization of aniline can be used to electrically bridge initially independent platinum electrodes. As this application requires a polyaniline bridge to form over a nonconductive material before an electrical contact is obtained, polyaniline growth using chemical oxidative reaction is investigated on substrates presenting surface-tension contrast patterns.

Evaluation of the BYG Carba Test, a New Electrochemical Assay for Rapid Laboratory Detection of Carbapenemase-Producing Enterobacteriaceae.

ABSTRACT Accurate detection of carbapenemase-producing Enterobacteriaceae (CPE) constitutes a major laboratory diagnostic challenge. We evaluated an electrochemical technique (the BYG Carba test) which allows detection of CPE in less than 35 min. The BYG Carba test was first validated in triplicate against 57 collection isolates with previously characterized β-lactam resistance mechanisms (OXA-48, n = 12; KPC, n = 8; NDM, n = 8; VIM, n = 8; IMP, n = 3; GIM, n = 1; GES-6, n = 1; no carbapenemase, n = 16) and against a panel of 10 isolates obtained from the United Kingdom National External Quality Assessment Service (NEQAS). The test was then evaluated prospectively against 324 isolates referred to the national reference center for suspicion of CPE. The BYG Carba test results were compared with those obtained with the Carba NP test using multiplex PCR sequencing as the gold standard. Of the 57 collection and the 10 NEQAS isolates, all but one GES-6-producing isolate were correctly identified by the Carba BYG test. Among the 324 consecutive Enterobacteriaceae isolates tested prospectively, 146 were confirmed as noncarbapenemase producers by PCR while 178 harbored a carbapenemase gene (OXA-48, n = 117; KPC, n = 25; NDM, n = 23; and VIM, n = 13). Prospectively, in comparison with PCR results, the BYG Carba test displayed 95% sensitivity and 100% specificity versus 89% and 100%, respectively, for the Carba NP test. The BYG Carba test is a novel, rapid, and efficient assay based on an electro-active polymer biosensing technology discriminating between CPE and non-CPE. The precise electrochemical signal (electrochemical impedance variations) allows the establishment of real-time objective measurement and interpretation criteria which should facilitate the accreditation process of this technology.

Bifunctional microstructured films and surfaces obtained by soft lithography from breath figure arrays

Breath figure films of polystyrene and polyalkylthiophene presenting regular patterns of 600 nm and 5 µm are used as templates to prepare negative polydimethylsiloxane stamps containing an entrapped quantity of the primary polymer. These breath figure replica are used to generate single or double layers of the entrapped conjugated polymer in the form of networks on any substrates. Besides this, polystyrene printed in this way can be used as a resist mask that allows the polymerization of aniline in a regular micrometric arrangement on a platinum electrode or to generate a regular acid/base patterning on a plain polyaniline film.

Simultaneous Determination of Cadmium (II) and Zinc (II) by Molecular Fluorescence Spectroscopy and Multiple Linear Regression Using an Anthrylpentaazamacrocycle Chemosensor

The work that is reported here concerns a method that allows the simultaneous determination of cadmium (II) and zinc (II) in aqueous solution by molecular fluorescence spectroscopy using 9-(1′,4′,7′,10′,13′-pentaazacyclopentadecyl)-methylanthracene. For this chemosensor, the fluorophore π-system is insulated from an azacrown donor by one methylene group. A self-quenching mechanism, resulting from an electron transfer from the nitrogens of the azacrown to the excited aromatic system, essentially precludes fluorescence emission. Fluorescence is restored when cadmium (II) or zinc (II) are chelated by the macrocycle. The difference between the emission spectra profiles of the free chemosensor, the cadmium and the zinc chelates is such that the concentration determination of the two metals and the remaining free chemosensor is possible at the nanomolar scale in only one experiment using a multiple linear regression algorithm. Usefulness and convenience of this simple method is proven by steady state and kinetic quantitative determination experiments.