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In this technical note, we demonstrate a squeeze-film based spacer-free method for creating controllable submicrometer hydrogel films on planar substrates that can be used to photolithographically fabricate hydrogel microstructures. This new technique improves the photolithographic resolution and yield by providing a uniform and low-defect hydrogel film. The optimum polymerization initiation time for achieving such a layer was determined to be around 1 min. For patterning, the dried hydrogel film was coated with a parylene-C masking layer. Subsequent etching in oxygen plasma was used to transfer selected patterns of hydrogel to the substrate in a batch scale. 10.1021/ac100579v

We present the first known implementation of a passive, scalable architecture for trapping, imaging, and sorting individual microparticles, including cells, using a positive dielectrophoretic (p-DEP) trapping array. Our array-based technology enables 'active coverslips' where, when scaled, many individually held cells can be sorted based upon imaged spatial or temporally variant characteristics. Our design incorporates a unique 'ring-dot' p-DEP trap geometry organized in a row/column array format. This trap design, implemented in a two-level metal process, provides strong and highly spatially localized holding fields enabling single-cell capture for all traps in the array. We release individual trapped microparticles during sorting using a passive transistor-independent approach where we electrically ground the row and column electrodes associated with specific traps in the array. The demand for chip-to-world electrical connections in our arrays scales proportionally with the square root of the number of traps in a given array, delivering a substantial improvement over prior designs. We demonstrate capture, holding, and release operations with both beads and cells in small arrays of this new architecture.

We previously introduced a vacuum deposition interface for matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI/TOF MS) on a moving surface (e.g., quartz wheel, Mylar tape, metal target). In our present work, the approach has been extended to demonstrate parallel analysis for multiple on-line infusion MALDI MS and capillary array electrophoresis (CAE)-MALDI MS. In the infusion mode, individual peptide samples were simultaneously deposited on a Mylar tape cartridge using an array of eight capillaries, yielding eight parallel traces. For CAE-MALDI/TOF MS, the same number of separation capillaries were coupled with an array of eight infusion capillaries using a common liquid junction, containing matrix solution. A fast-scanning mirror was employed to traverse the beam of the desorption laser across the Mylar tape to probe one trace at a time. The positions of the eight sample traces formed on the tape were automatically determined, and all samples were analyzed in rapid sequence using a kilohertz repetition rate laser and a high-throughput data acquisition system. The instrumentation was operated with CAE MS for high-throughput analysis without compromising data quality. The principles of parallel separation--vacuum deposition should be generally applicable to MALDI/TOF MS analysis for proteomics and other areas where separation and high throughput are required.

The preparation of Pt-group metal films on roughened gold electrodes by utilizing spontaneous redox replacement of an underpotential-deposited (upd) copper or lead monolayer with a Pt-group metal cation solute is described. The resulting films display intense surface-enhanced Raman scattering (SERS) for adsorbates bound to the overlayer and free from substrate interferences. This strategy provides a useful alternative, at least for platinum, to the constant-current electrodeposition method commonly utilized to prepare SERS-active Pt-group metal films (Zou, S.; Weaver, M. J. Anal. Chem. 1988, 70. 2387). Similarly to related earlier studies, the film uniformity (specifically, the absence or otherwise of residual Au 'pinhole' sites) was tested by employing carbon monoxide, and also ethylene, as 'probe' chemisorbates, since they yield vibrational frequencies on Au that are blue-shifted from the corresponding bands for adsorbate bound to Pt-group metal sites. While a single redox replacement of upd Cu with Pt(IV) yielded incomplete surface coverage, as expected, the use of multiple (up to eight) replacement cycles produced Pt films displaying remarkably intense CO vibrational bands as well as apparently 'pinhole-free' properties, although such imperfections were detected with the ethylene probe. A single upd Cu replacement with Pt(II), however, yielded a remarkably uniform Pt layer, as indicated by pinhole-free characteristics using both the CO and ethylene probes along with the voltammetric behavior. The use of additional redox replacement cycles yielded marked progressive attenuation in the SERS signals. Comparable, although less optimal, SERS behavior was obtained for Pd films prepared similarly from Pd(II). The value of the strategy for exploring catalytic as well as equilibrium adsorptive chemistry on Pt surfaces is also illustrated.

Ionic substances with melting points at or close to room temperature are referred to as ionic liquids. Interest in ionic liquids for their potential in different chemical processes is increasing, because they are environmentally benign and are good solvents for a wide range of both organic and inorganic materials. In this study, a capillary electrophoretic method for resolving phenolic compounds found in grape seed extracts is reported. The method, in which 1-alkyl-3-methylimidazolium-based ionic liquids are used as the running electrolytes, is simple and reproducible. The separation mechanism seems to involve association between the imidazolium cations and the polyphenols. The role of the alkyl substituents on the imidazolium cations was investigated and will be discussed.