Synthesis and Identification of Biologically Active Mono-Labelled FITC-Insulin Conjugate

Fluorescently labelling proteins such as insulin have wide ranging applications in a pharmaceutical research and drug delivery. Human insulin (Actrapid®) was labelled with fluorescein isothiocyanate (FITC) and the synthesised conjugate identified using reverse phase high performance liquid chromatography (RP-HPLC) on a C18 column and a gradient method with mobile phase A containing 0.1% trifluoroacetic acid (TFA) in Millipore water and mobile phase B containing 90% Acetonitrile, 10% Millipore water and 0.1% TFA. Syntheses were carried out at varying reaction times between 4 and 20 h. Mono-labelled FITC-insulin conjugate was successfully synthesised with labelling at the B1 position on the insulin chain using a molar ratio of 2:1 (FITC:insulin) at a reaction time of 18 h and confirmed by electrospray mass spectroscopy. Reactions were studied across a pH range of 7-9.8 and the quantities switch from mono-labelled to di-labelled FITC-insulin conjugates at a reaction time of 2 h (2:1 molar ratio) at pH > 8. The conjugates isolated from the studies had biological activities in comparison to native insulin of 99.5% monoB1, 78% monoA1, 51% diA1B1 and 0.06% triA1B1B29 in HUVEC cells by examining AKT phosphorylation levels. MonoB1 FITC-insulin conjugate was also compared to native insulin by examining cell surface GLUT4 in C2C12 skeletal muscle cells. No significant difference in the cellular response was observed for monoB1 produced in-house compared to native insulin. Therefore mono-labelled FITC-insulin at the B1 position showed similar biological activity as native insulin and can potentially be used for future biomedical applications.

Coating gigaporous polystyrene microspheres with cross-linked poly(vinyl alcohol) hydrogel as a rapid protein chromatography matrix

Gigaporous polystyrene (PS) microspheres were hydrophilized by in situ polymerization to give a stable cross-linked poly(vinyl alcohol) (PVA) hydrogel coating, which can shield proteins from the hydrophobic PS surface underneath. The amination of microspheres (PS-NH2) was first carried out through acetylization, oximation and reduction, and then 4,4'-azobis (4-cyanovaleric acid) (ACV), a polymerization initiator, was covalently immobilized on PS-NH2 through amide bond formation, and the cross-linked poly(vinyl acetate) (PVAc) was prepared by radical polymerization at the surfaces of ACV-immobilized PS microspheres (PS-ACV). Finally, the cross-linked PVA hydrogel coated gigaporous PS microspheres (PS-PVA) was easily achieved through alcoholysis of PVAc. Results suggested that the PS microspheres were effectively coated with cross-linked PVA hydrogel, where the gigaporrous structure remained under optimal conditions. After hydrophilic modification (PS-PVA), the protein-resistant ability of microspheres was greatly improved. The hydroxyl-rich PS-PVA surface can be easily derivatized by classical chemical methods. Performance advantages of the PS-PVA column in flow experiment include good permeability, low backpressure, and mechanical stability. These results indicated that PS-PVA should be promising in rapid protein chromatography.

Continuous-flow single-molecule CE with high detection efficiency

This paper describes the use of two-beam line-confocal detection geometry for measuring the total mobility of individual molecules undergoing continuous-flow CE separation. High-sensitivity single-molecule confocal detection is usually performed with a diffraction limited focal spot (approximately 500 nm in diameter), which necessitates the use of nanometer-sized channels to ensure all molecules flow through the detection volume. To allow for the use of larger channels that are a few micrometers in width, we employed cylindrical optics to define a rectangular illumination area that is diffraction-limited (approximately 500 nm) in width, but a few micrometers in length to match the width of the microchannel. We present detailed studies that compare the performance of this line-confocal detection geometry with the more widely used point-confocal geometry. Overall, we found line-confocal detection to provide the highest combination of signal-to-background ratio and spatial detection efficiency when used with micrometer-sized channels. For example, in a 2 microm wide channel we achieved a 94% overall detection efficiency for single Alexa488 dye molecules when a 2 microm x 0.5 microm illumination area was used, but only 34% detection efficiency with a 0.5 microm-diameter detection spot. To carry out continuous-flow CE, we used two-beam fluorescent cross-correlation spectroscopy where the transit time of each molecule is determined by cross-correlating the fluorescence registered by two spatially offset line-confocal detectors. We successfully separated single molecules of FITC, FITC-tagged glutamate, and FITC-tagged glycine.

Characterization and performance of injection molded poly(methylmethacrylate) microchips for capillary electrophoresis

Injection molded poly(methylmethacrylate) (IM-PMMA), chips were evaluated as potential candidates for capillary electrophoresis disposable chip applications. Mass production and usage of plastic microchips depends on chip-to-chip reproducibility and on analysis accuracy. Several important properties of IM-PMMA chips were considered: fabrication quality evaluated by environmental scanning electron microscope imaging, surface quality measurements, selected thermal/electrical properties as indicated by measurement of the current versus applied voltage (I-V) characteristic and the influence of channel surface treatments. Electroosmotic flow was also evaluated for untreated and O2 reactive ion etching (RIE) treated surface microchips. The performance characteristics of single lane plastic microchip capillary electrophoresis (MCE) separations were evaluated using a mixture of two dyes-fluorescein (FL) and fluorescein isothiocyanate (FITC). To overcome non-wettability of the native IM-PMMA surface, a modifier, polyethylene oxide was added to the buffer as a dynamic coating. Chip performance reproducibility was studied for chips with and without surface modification via the process of RIE with O2 and by varying the hole position for the reservoir in the cover plate or on the pattern side of the chip. Additionally, the importance of reconditioning steps to achieve optimal performance reproducibility was also examined. It was found that more reproducible quantitative results were obtained when normalized values of migration time, peak area and peak height of FL and FITC were used instead of actual measured parameters.

Nanoliter capillary electrochromatography columns based on collocated monolithic support structures molded in poly(dimethyl siloxane)

Following current trends in miniaturization of analytical chemistry, an inexpensive disposable analytical tool in the form of a liquid chromatography column fabricated on a poly(dimethyl siloxane) (PDMS) chip was created. Ease of fabricating the chromatography column was demonstrated by molding collocated monolithic support structures (COMOSS) directly in the column. Positive photo-resist, SPR 220, was used to create column structures on a negative relief master providing final channel dimensions of 2.7-5.2 microm wide by 10.0 microm deep, while monolithic dimensions were 9.8 x 9.8 x 10.0 microm - 12.3 x 12.3 x 10.0 microm. The ability to separate biological samples such as peptides from a tryptic digest of fluorescein isothiocyanate labeled bovine serum albumin (FITC-BSA) was shown. Separations in capillary electrochromatographic (CEC) mode were performed yielding column efficiencies of 4.0 x 10(5) plates/m.

Partition and permeation of dextran in polyacrylamide gel

Partition of sized FITC-dextrans in polyacrylamide gel showed a relationship between Kav and solute radius as predicted by the theory of Ogston, which is based solely on geometry of the spaces. Permeability data for the same dextrans were fit to several theories, including those based on geometry and those based on hydrodynamic interactions, and the gel structure predicted by the partition and permeability data were compared. The Brinkman effective-medium model (based on hydrodynamic interactions and requiring a measure of the hydraulic conductivity of the matrix) gave the best fit of permeability data with the values for fiber radius (rf) and void volume of the gel (epsilon) that were obtained from the partition data. The models based on geometry and the hydrodynamic screening model of Cukier, using the rf and epsilon from partition data, all predicted higher rates of permeation than observed experimentally, while the effective-medium model with added term for steric interaction predicted lower permeation than that observed. The size of cylindrical pores appropriate for the partition data predicted higher rates of permeation than observed. These relative results were unaffected by the method of estimating void volume of the gel. In sum, it appears that one can use data on partition of solute, combined with measurement of hydraulic conductivity, to predict solute permeation in polyacrylamide gel.