Cell detection and counting through cell lysate impedance spectroscopy in microfluidic devices

Cell-based microfluidic devices have attracted interest for a wide range of applications. While optical cell counting and flow cytometry-type devices have been reported extensively, sensitive and efficient non-optical methods to detect and quantify cells attached over large surface areas within microdevices are generally lacking. We describe an electrical method for counting cells based on the measurement of changes in conductivity of the surrounding medium due to ions released from surface-immobilized cells within a microfluidic channel. Immobilized cells are lysed using a low conductivity, hypotonic media and the resulting change in impedance is measured using surface patterned electrodes to detect and quantify the number of cells. We found that the bulk solution conductance increases linearly with the number of isolated cells contributing to solution ion concentration. The method of cell lysate impedance spectroscopy is sensitive enough to detect 20 cells microL(-1), and offers a simple and efficient method for detecting and enumerating cells within microfluidic devices for many applications including measurement of CD4 cell counts in HIV patients in resource-limited settings. To our knowledge, this is the most sensitive approach using non-optical setups to enumerate immobilized cells. The microfluidic device, capable of isolating specific cell types from a complex bio-fluidic and quantifying cell number, can serve as a single use cartridge for a hand-held instrument to provide simple, fast and affordable cell counting in point-of-care settings.     

Stereoselective synthesis of a MCHr1 antagonist

Melanin-concentrating hormone (MCH) is implicated in the feeding behavior in mammals affording a potential target to control overeating in people. Compound 1 (AMG 076) has been identified as a potent MCHr1 antagonist for the treatment of obesity. A synthesis suitable for the large-scale preparation of this lead candidate was developed to support preclinical studies. A Robinson annulation of benzylpiperidone and resolution of the desired enone from a mixture of the diastereomers afforded key intermediate 6 after a stereoselective hydrogenation. Subsequent Fischer indole synthesis with hydrazine 5 then provided the advanced intermediate, indole 2. Two complementary reductive amination strategies employing either aldehyde 3 or lactol 4 led to the synthesis of title compound 1.     

New features in the class of association models

The most common association models are the U-, R-, C- and RC-models, achieved when only one dimension on the association is considered as significant (M = 1). Whenever more than one dimensions are significant (M > 1), the only kind of association assumed for each dimension is of the RC-type with the exception of Goodman's R + C + RC, R + RC, C + RC, U + RC and R + C models. Extending the idea of U-, R-, and C-models to association models with M > 1, relaxing the equidistance principle for successive categories for the known scores and using orthogonal polynomials, some new models are developed. Two classical sets of data are used to illustrate the advantages of the newly introduced models. Comparisons in terms of chi-square goodness of fit indicate that some of the newly introduced models perform better than the models fitted so far on these data sets. © 1998 John Wiley & Sons, Ltd.     

Generalized holographic dark energy model

In this paper, the model of the holographic Chaplygin gas has been extended to two general cases: first the case of a modified variable Chaplygin gas and second the case of the viscous generalized Chaplygin gas. The dynamics of the model is expressed by the use of scalar fields and scalar potentials.     

A mild,efficient and selective iodination of aromatic compounds using iodine and 1,4-bis(triphenylphosphonium)-2-butene peroxodisulfate

A simple and efficient method for the iodination of aromatic compounds has been achieved in the presence of iodine and 1,4-bis(triphenylphosphonium)-2-butene peroxodisulfate.     

On the commutativity degree of compact groups

In any finite group G, the commutativity degree of G (denoted by d(G)) is the probability that two randomly chosen elements of G commute. More generally, for every n ≥ 2 the nth commutativity degree (denoted by d _n (G)) is the probability that a randomly chosen ordered (n + 1)-tuple of the group elements is mutually commuting. The aim of this paper is to generalize the definition of d(G) and d _n (G) to every compact group G (infinite and even uncountable). We shall state some results concerning compact groups and we will extend some results in Erfanian et al. (Comm. Algebra 35 (2007), 4183–4197) and Lescot (J. Algebra 177 (1995), 847–869).     

Fixed point for set-valued mappings satisfying an implicit relation in partially ordered metric spaces

Let (X,?) be a partially ordered set and d be a complete metric on X. Let F,G be two set-valued mappings on X. We obtained sufficient conditions for the existence of common fixed point of F and G satisfying an implicit relation in partially ordered set X.     

Surface-directed boundary flow in microfluidic channels

Channel geometry combined with surface chemistry enables a stable liquid boundary flow to be attained along the surfaces of a 12 microm diameter hydrophilic glass fiber in a closed semi-elliptical channel. Surface free energies and triangular corners formed by PDMS/glass fiber or OTS/glass fiber surfaces are shown to be responsible for the experimentally observed wetting phenomena and formation of liquid boundary layers that are 20-50 microm wide and 12 microm high. Viewing this stream through a 20 microm slit results in a virtual optical window with a 5 pL liquid volume suitable for cell counting and pathogen detection. The geometry that leads to the boundary layer is a closed channel that forms triangular corners where glass fiber and the OTS coated glass slide or PDMS touch. The contact angles and surfaces direct positioning of the fluid next to the fiber. Preferential wetting of corner regions initiates the boundary flow, while the elliptical cross-section of the channel stabilizes the microfluidic flow. The Young-Laplace equation, solved using fluid dynamic simulation software, shows contact angles that exceed 105 degrees will direct the aqueous fluid to a boundary layer next to a hydrophilic fiber with a contact angle of 5 degrees. We believe this is the first time that an explanation has been offered for the case of a boundary layer formation in a closed channel directed by a triangular geometry with two hydrophobic wetting edges adjacent to a hydrophilic surface.     

Synthesis of spongy gold nanocrystals with pronounced catalytic activities

A simple and easier chemical method for preparing spongy gold nanocrystals has been developed on the basis of a modified-citrate reduction technique of the corresponding gold salt at 25 degrees C in the absence of template. These nanocrystals possessed autocatalytic behavior and exhibited pronounced catalytic activity in the borohydride reduction of 4-nitrophenol due to their unique spongy morphology.