Plastic materials have the potential to substitute for glass substrates used in microfluidic and microTAS systems adding flexibility in materials' choices. Optical quality plastic materials with a low autofluorescence are crucial for optimal detection by fluorescence and laser induced fluorescence techniques. This paper summarizes a series of optical investigations on commercially available plastic chip materials (PMMA, COC, PC, PDMS) and chips made from those materials. Intrinsic optical constants of plastic materials-refractive index for bulk materials-determined by spectroscopic ellipsometry and transmission spectroscopy in the visible range are presented. The laser-induced autofluorescence of materials and chips was assessed at four laser wavelengths, namely, 403, 488, 532 and 633 nm. Considerable bleaching of the autofluorescence was observed under continuous laser illumination. Overall, the longer wavelength laser excitation sources yielded less autofluorescence. PDMS exhibited the least autofluorescence and was comparable to BoroFloat glass. In all cases, chips exhibited slightly higher autofluorescence than the raw plastic materials from which they had been made.

No abstract

SummaryAn LC-MS method based on the use of high resolution Fourier transform ion cyclotron resonance mass spectrometry (FTIRCMS) for profiling oligonucleotides synthesis impurities is described.Oligonucleotide phosphorothioatediesters (phosphorothioate oligonucleotides), in which one of the non-bridging oxygen atoms at each phosphorus center is replaced by a sulfur atom, are now one of the most popular oligonucleotide modifications due to their ease of chemical synthesis and advantageous pharmacokinetic properties. Despite significant progress in the solid-phase oligomerization chemistry used in the manufacturing of these oligonucleotides, multiple classes of low-level impurities always accompany synthetic oligonucleotides. Liquid chromatography-mass spectrometry has emerged as a powerful technique for the identification of these synthesis impurities. However, impurity profiling, where the entire complement of low-level synthetic impurities is identified in a single analysis, is more challenging. Here we present an LC-MS method based the use of high resolution-mass spectrometry, specifically Fourier transform ion cyclotron resonance mass spectrometry (FTIRCMS or FTMS). The optimal LC-FTMS conditions, including the stationary phase and mobile phases for the separation and identification of phosphorothioate oligonucleotides, were found. The characteristics of FTMS enable charge state * To whom correspondence should be addressed. Phone (513) 556-1871, Fax (513) 556-9239, Pat.Limbach@uc.edu.Publisher's Disclaimer: This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final citable form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain. NIH Public Access Author ManuscriptInt J Mass Spectrom. Author manuscript; available in PMC 2012 July 1.

The use of traditional capillary electrophoresis (CE) to detect weak binding complexes is problematic due to the fast-off rate resulting in the dissociation of the complex during the separation process. Additionally, proteins involved in binding interactions often nonspecifically stick to the bare-silica capillary walls, which further complicates the binding analysis. Microchip CE allows flexibly positioning the detector along the separation channel and conveniently adjusting the separation length. A short separation length plus a high electric field enables rapid separations thus reducing both the dissociation of the complex and the amount of protein loss due to nonspecific adsorption during the separation process. Thrombin and a selective thrombinbinding aptamer were used to demonstrate the capability of microchip CE for the study of relatively weak binding systems that have inherent limitations when using the migration shift method or other CE methods. The rapid separation of the thrombin-aptamer complex from the free aptamer was achieved in less than 10 s on a single-cross glass microchip with a relatively short detection length (1.0 cm) and a high electric field (670 V/cm). The dissociation constant was determined to be 43 nM, consistent with reported results. In addition, aptamer probes were used for the quantitation of standard thrombin samples by constructing a calibration curve, which showed good linearity over two orders of magnitude with a limit of detection for thrombin of 5 nM at a 3-fold signal-to-noise ratio.

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 O 2 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 O 2 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

A passive microfluidic mixer with high performance is designed and fabricated in this work. Diamond-shaped obstacles were chosen to split the flow into several streams, which are then guided back together after the obstacle. To keep pressure drop low, the channel cross-sectional area was maintained equal to the input cross-sectional area, and this was held constant throughout the device. The proposed design was modeled using computational fluid dynamics (CFD) software. The effects of channel width, channel length, location of obstructions, and Reynolds Number (Re) were investigated. The simulated results were verified experimentally. Simulation data showed that the designed micromixer achieved 90% mixing at a channel length of 4.35 mm with pressure drop of 584 Pa at Re = 1, while experimental data for Re = 0.1 showed 90% mixing at 7 mm. The mixer functions well especially at the low Re (Re = 0.1).

Biphasic calcium phosphate/poly-L-lactide granules of 150-200 mm sizes were subjected to high-energy mechanical milling in a planetary ball mill for up to 480 minutes. Characterization of the material obtained was carried out using X-ray diffraction (XRD), differential scanning calorimetry (DSC), environmentally scanning electronic microscopy (ESEM), transmission electron microscopy (TEM) and infrared spectroscopy (IR). These techniques confirmed that mechanical milling induced significant changes in the biocomposite structure and properties. The most significant changes are reduction of the HAp crystallites size from 99.8 to 26.7 nm and -TCP from 97.3 to 29.6, as well as crystallinity of PLLA phases. Homogeneous phase distribution (arrangement) is obtained by extending the duration of mechanical milling.

Fluorescently labeled beads may be utilized in transparent microfluidic devices to facilitate a variety of immunoassay based chemical measurements. We investigate the ability to visualize, quantitate, and reduce undesirable adsorption of beads within a polydimethylsiloxane (PDMS) microchannel device. These methods are prerequisites to the design of practical bead-based microfluidic sensing devices. The PDMS microchannels were shown to be transparent enough to make accurate quantitative optical measurements, although significant adsorption was observed. Epifluorescence microscopy was employed in an attempt to quantitatively evaluate microbead adsorption to PDMS microchannel walls and bulk surfaces after different agitation, solution, and surface treatments. This microscopy method provides reproducible imaging of individual beads and allows for characterization of adsorption to PDMS microchannel walls. Solution composition seemed to play a more important role in the ability to reduce the number of adsorbed beads to the PDMS surface than agitation. The most significant reduction in bead adsorption was seen in surface treatment. The most effective surface treatment examined in this study was Teflon AF.