@article {228, title = {A rapid diffusion immunoassay in a T-sensor.}, journal = {Nat Biotechnol}, volume = {19}, year = {2001}, month = {2001 May}, pages = {461-5}, abstract = {

We have developed a rapid diffusion immunoassay that allows measurement of small molecules down to subnanomolar concentrations in <1 min. This competitive assay is based on measuring the distribution of a labeled probe molecule after it diffuses for a short time from one region into another region containing antigen-specific antibodies. The assay was demonstrated in the T-sensor, a simple microfluidic device that places two fluid streams in contact and allows interdiffusion of their components. The model analyte was phenytoin, a typical small drug molecule. Clinically relevant levels were measured in blood diluted from 10- to 400-fold in buffer containing the labeled antigen. Removal of cells from blood samples was not necessary. This assay compared favorably with fluorescence polarization immunoassay (FPIA) measurements. Numerical simulations agree well with experimental results and provide insight for predicting assay performance and limitations. The assay is homogeneous, requires <1 microl of reagents and sample, and is applicable to a wide range of analytes.

}, keywords = {Antibody Specificity, Antigen-Antibody Complex, Binding, Competitive, Diffusion, Fluorescence Polarization Immunoassay, Immunoassay, Molecular Weight, Phenytoin, Rheology}, issn = {1087-0156}, doi = {10.1038/88135}, author = {Hatch, A and Kamholz, A E and Hawkins, K R and Munson, M S and Schilling, E A and Weigl, B H and Yager, P} } @article {229, title = {Quantitative analysis of molecular interaction in a microfluidic channel: the T-sensor.}, journal = {Anal Chem}, volume = {71}, year = {1999}, month = {1999 Dec 1}, pages = {5340-7}, abstract = {

The T-sensor is a recently developed microfluidic chemical measurement device that exploits the low Reynolds number flow conditions in microfabricated channels. The interdiffusion and resulting chemical interaction of components from two or more input fluid streams can be monitored optically, allowing measurement of analyte concentrations on a continuous basis. In a simple form of T-sensor, the concentration of a target analyte is determined by measuring fluorescence intensity in a region where the analyte and a fluorescent indicator have interdiffused. An analytical model has been developed that predicts device behavior from the diffusion coefficients of the analyte, indicator, and analyte--indicator complex and from the kinetics of the complex formation. Diffusion coefficients depend on the local viscosity which, in turn, depends on local concentrations of all analytes. These relationships, as well as reaction equilibria, are often unknown. A rapid method for determining these unknown parameters by interpreting T-sensor experiments through the model is presented.

}, keywords = {Kinetics, Models, Chemical, Spectrometry, Fluorescence}, issn = {0003-2700}, author = {Kamholz, A E and Weigl, B H and Finlayson, B A and Yager, P} } @article {31, title = {Formation of high axial ratio microstructures from peptides modified with glutamic acid dialkyl amides.}, journal = {Biochim Biophys Acta}, volume = {1371}, year = {1998}, month = {1998 May 28}, pages = {168-84}, abstract = {

A growing number of amphiphiles are known to form high axial ratio microstructures (HARMs) such as the hollow cylindrical microstructures called lipid tubules. As a prelude to exploring the potential of HARMs formed from lipopeptides in controlled release drug delivery, several microstructure formation conditions were investigated. We report the preparation of several glutamic acid dialkyl amides with varying alkyl chain lengths bearing a verity of peptides (1-4 amino acids) [peptide-Glu-(NHCnH2n+1)2, n=12, 14, 16]. These surfactants have been rapidly and efficiently converted into HARMs in aqueous buffer at physiological pH and ionic strength, or in buffer containing MeOH or EtOH. Helical ribbons and tubular HARMs were produced that were stable for as long as 6 months below the phase transition temperatures of the compounds. To estimate the stability of HARMs in vivo, HARMs formed from (Pro)3-Glu(NHC16H33)2 were incubated with DOPC liposomes or fetal calf serum at 40 degreesC. HARM size and shape did not change significantly, suggesting that such lipopeptide particles can retain their morphology long enough in vivo to be useful as drug delivery vehicles.

}, keywords = {Amides, Calorimetry, Differential Scanning, Drug Carriers, Drug Stability, Glutamic Acid, Light, Lipoproteins, Liposomes, Peptides, Cyclic, Phosphatidylcholines, Scattering, Radiation}, issn = {0006-3002}, author = {Lee, K C and Lukyanov, A N and Gelb, M H and Yager, P} } @article {32, title = {Formation of high-axial-ratio-microstructures from natural and synthetic sphingolipids.}, journal = {Chem Phys Lipids}, volume = {88}, year = {1997}, month = {1997 Aug 8}, pages = {21-36}, abstract = {

Amphiphiles that form high-axial-ratio-microstructures (HARMs) are being considered as novel materials for controlled release of drugs and other biologically functional molecules. HARMs consisting of tubules, ribbons, solid rods and helices are formed from sphingolipids by addition of water to a solution of amphiphile in DMF. Single molecular species of galactocerebroside (GalCer) containing long unsaturated fatty acid chains or natural GalCer containing mixed-length, non-hydroxy fatty acids (NFA-GalCer) or alpha-hydroxy fatty acids (HFA-GalCer) form cylindrical structures. In contrast, single molecular species of GalCer containing long saturated fatty acids form ribbons and helices. GalCer HARMs are typically under 100 nm in diameter and have lengths of several microns. The importance of the amide of GalCer for HARM formation was evaluated using psychosine, which forms solid fibers, whereas sphingosine and an analog of GalCer in which the amide is reduced to a secondary amine form amorphous aggregates. Single molecular species of ceramide containing long unsaturated fatty acid chains form cylindrical structures, whereas those with long saturated fatty acids form ribbons and helices. Short chain saturated ceramide also forms cylindrical structures. GalCer analogs with N-acetyl-glycine in place of the galactose form fibers whereas those with N-acetyl-proline yield amorphous material. The N-acetyl-proline-containing amphiphile can de doped into pure GalCer or NFA-GalCer without perturbing tubule formation.

}, keywords = {Amides, Amino Acids, Calorimetry, Differential Scanning, Ceramides, Delayed-Action Preparations, Fatty Acids, Galactosylceramides, Sphingolipids}, issn = {0009-3084}, author = {Goldstein, A S and Lukyanov, A N and Carlson, P A and Yager, P and Gelb, M H} }