Embedded passivated-electrode insulator-based dielectrophoresis (EπDEP)

Here, we introduce a new technique called embedded passivated-electrode insulator-based dielectrophoresis (EπDEP) for preconcentration, separation, or enrichment of bioparticles, including living cells. This new method combines traditional electrode-based DEP and insulator-based DEP with the objective of enhancing the electric field strength and capture efficiency within the microfluidic channel while alleviating direct contact between the electrode and the fluid. The EπDEP chip contains embedded electrodes within the microfluidic channel covered by a thin passivation layer of only 4 μm. The channel was designed with two nonaligned vertical columns of insulated microposts (200 μm diameter, 50 μm spacing) located between the electrodes (600 μm wide, 600 μm horizontal spacing) to generate nonuniform electric field lines to concentrate cells while maintaining steady flow in the channel. The performance of the chip was demonstrated using Gram-negative (Escherichia coli) and Gram-positive (Staphylococcus aureus) bacterial pathogens in aqueous media. Trapping efficiencies of 100 % were obtained for both pathogens at an applied AC voltage of 50 V peak-to-peak and flow rates as high as 10 μl/min.     

On the keto-enol tautomerization of malonaldehyde: an effective fragment potential study

Recent studies have mapped the keto-enol tautomerization of malonaldehyde through a general transition structure that leads exclusively to the Z isomer of the enol. However, it will be shown that a competing general transition structure exists that leads to both the E and Z isomers of the enol at the B3LYP/6-31G(d,p) and MP2/6-31G(d,p) levels of theory. Both the RHF- and DFT-based effective fragment potential methods have been used to model solvation effects, and the results are compared with full ab initio calculations. It is found that two bridging water molecules with two discrete DFT-based effective fragment potential solvent waters at the MP2/6-31G(d,p) level of ab initio theory provides the most computationally effective model for solvent effects in this system. It is shown that the relative energies for this QM/MM model differ from the full MP2/6-31G(d,p) energies by an average absolute relative difference of 2.2 kcal mol-1 across the reaction path when the zero-point vibrational energy correction is included.     

Model for the photooxidation of parylenes

Parylenes belong to a family of polymers that have been investigated for use in electronic and medical applications. The photooxidation of these materials is of interest both to prevent degradation and to induce targeted chemical changes. This article describes a transport and reaction model for the photooxidation of parylenes. This model is based on existing polymer photooxidation mechanisms that have been adapted to this system. The model has been compared with existing parylene photooxidation data for this system and shows qualitative agreement with surface oxidation profiles and oxidation depth profiles. On the basis of the results of the model comparison, it has been determined that the key parameters that appear to affect the photooxidation of parylenes are the diffusion coefficient of oxygen in these films and the concentration of oxygen initially present in these films. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 2666–2677, 2004     

Characterization of parylene‐N and parylene‐C photooxidation

Parylene‐N and parylene‐C are polymers of interest for microelectronic and medical coating applications. Modifications for improved surface properties could make them even more useful in such applications. Parylene‐N and parylene‐C films were exposed to ultraviolet light in the presence of oxygen and analyzed with Rutherford backscattering spectrometry, secondary‐ion mass spectroscopy, X‐ray photoelectron spectroscopy, and infrared spectroscopy. This study shows that such exposure results in the formation of aldehyde and carboxylic acid groups near the surface of the films. At the maximum exposure dose, the concentration of oxygen in both parylene‐N and parylene‐C is about 13% at the film surface, and it decreases exponentially with increasing depth. Further modeling and optimization of this process would allow it to be used to tailor the surface concentration of oxygenated species in parylene for the optimization of adhesion and wettability or for the chemical binding of other moieties. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 1486–1496, 2003     

3D Insulator‐based dielectrophoresis using DC‐biased,AC electric fields for selective bacterial trapping

Insulator‐based dielectrophoresis (iDEP) is a well‐known technique that harnesses electric fields for separating, moving, and trapping biological particle samples. Recent work has shown that utilizing DC‐biased AC electric fields can enhance the performance of iDEP devices. In this study, an iDEP device with 3D varying insulating structures analyzed in combination with DC biased AC fields is presented for the first time. Using our unique reactive ion etch lag, the mold for the 3D microfluidic chip is created with a photolithographic mask. The 3D iDEP devices, whose largest dimensions are 1 cm long, 0.18 cm wide, and 90 μm deep are then rapidly fabricated by curing a PDMS polymer in the glass mold. The 3D nature of the insulating microstructures allows for high trapping efficiency at potentials as low as 200 Vpp. In this work, separation of Escherichia coli from 1 μm beads and selective trapping of live Staphylococcus aureus cells from dead S. aureus cells is demonstrated. This is the first reported use of DC‐biased AC fields to selectively trap bacteria in 3D iDEP microfluidic device and to efficiently separate particles where selectivity of DC iDEP is limited.     

Single-step purification of rat C-reactive protein and generation of monospecific C-reactive protein antibody

Although Sepharose-phosphorylcholine affinity chromatography has been used extensively to purify some acute phase proteins, the operation has usually been a laborious multi-step procedure. By modifying previously described multi-step protein purification assays, centigram quantities of pure rat C-reactive protein (CRP) could be obtained in a single chromatographic step using affinity chromatography. Rat serum was passed over a column of p-aminophenylphosphorylcholine and extraneous proteins eluted with Tris-saline-Ca2+ buffer. Similar to other purification procedures, CRP was eluted with phosphorylcholine in a Tris-saline-Ca2+ buffer. The technical detail which distinguished this procedure from others, was the use of a phosphorylcholine gradient shallow enough (0.95 mM-2.5 mM) to resolve the eluent into two peaks; the first peak was composed largely of the contaminant, serum amyloid protein (SAP), and the second was composed of CRP. Although there was some overlap between the first and second peak, pure CRP could be obtained by pooling fractions from the trailing shoulder of the second peak. Using this single step procedure, a greater than 25% yield of SAP-free, purified CRP could be obtained. The purified CRP was free of SAP contamination as measured by sodium dodecyl sulfate gradient polyacrylamide gel electrophoresis. Purified CRP was determined to be free of rat albumin, IgG and the C3 component of complement using immunoelectrophoresis. This one-step affinity column chromatography procedure provides a simple, efficient method for collecting large quantities of rat CRP pure enough to be used to obtain a monospecific goat, anti-rat CRP antibody.     

Separation of Bulk Carbon Dioxide-Hydrogen Mixtures by Selective Surface Flow Membrane

The separation performance of carbon dioxide-hydrogen mixtures by a nanoporous carbon membrane called selective surface flow membrane is described. The membrane selectively permeates CO2 from H2 and a H2 enriched gas is produced at the feed gas pressure. Extensive experimental data for the separation using feed gas pressures from 0.24 to 1.13 MPa and CO2 compositions from 5 to 75 (mol%) in H2 are reported. The data can be empirically correlated using a simple equation with a single adjustable-parameter. The adjustable parameter is found to be a linear function of the feed gas CO2 partial pressure.The membrane separates CO2-H2 mixture very efficiently even at a low total feed gas pressure (0.4 MPa). The membrane area required for a given separation decreases drastically with increasing feed gas pressure in the range of 0.24–0.92 MPa and then it becomes insensitive to the feed gas pressure.     

Raman spectral analysis of renal tissue: a novel application

Renal cell carcinoma (RCC) accounts for 85% of all primary renal cancers. The definitive diagnosis of RCC relies exclusively on the subjective pathological interpretation of the surgical specimen. In this study, we aimed to analyze renal tissue using objective Raman spectroscopy (RS). We obtained 15 pairs of RCC (T) and corresponding normal renal parenchymal tissues (N) from our biobank. There are three subtypes of RCC: clear cell RCC (ccRCC), papillary RCC (pRCC), and chromophobe RCC (cRCC). Five pairs of tissue of each subtype were enrolled. Fresh‐frozen sliced tissues were used for the RS detection. The Raman spectra between T and N were compared and analyzed using partial least squares (PLS) regression. Data for a total of 55 T and 58 N analyzable RS samples were obtained. The spectra were normalized by dividing the intensity of the characteristic peak at 1003 cm⁻¹ using phenylalanine's Raman peak. After further analysis with PLS, the sensitivity and specificity for discriminating T from N were 95% and 93%, respectively. The RCC subtypes can be discriminated at an accuracy of 72% for ccRCC, 88% for cRCC, and 86% for pRCC. This study demonstrates the feasibility of analyzing renal tissue using RS. RS, with its advantages of easy and objective tissue assessment, may be applied to aid intraoperative decision making and pathological tissue assessment. Copyright © 2014 John Wiley & Sons, Ltd.