Masoud Agah

High-performance temperature-programmed microfabricated gas chromatography columns

This paper reports the first development of high-performance, silicon-glass micro-gas chromatography (/spl mu/GC) columns having integrated heaters and temperature sensors for temperature programming, and integrated pressure sensors for flow control. These 3-m long, 150-/spl mu/m wide and 250-/spl mu/m deep columns, integrated on a 3.3 cm square die, were fabricated using a silicon-on-glass dissolved wafer process. Demonstrating the contributions to heat dissipation from conduction, convection, and radiation with and without packaging, it is shown that using a 7.5-mm high atmospheric pressure package reduces power consumption to about 650 mW at 100/spl deg/C, while vacuum packaging reduces the steady-state power requirements to less than 100 mW. Under vacuum conditions, 600 mW is needed for a temperature-programming rate of 40/spl deg/C/min. The 2300 ppm//spl deg/C TCR of the temperature sensors and the 50 fF/kPa sensitivity of the pressure sensors satisfy the requirements needed to achieve reproducible separations in a /spl mu/GC system. Using these columns, highly resolved 20-component separations were obtained with analysis times that are a factor of two faster than isothermal responses.

The effects of cancer progression on the viscoelasticity of ovarian cell cytoskeleton structures

UNLABELLED Alterations in the biomechanical properties and cytoskeletal organization of cancer cells in addition to genetic changes have been correlated with their aggressive phenotype. In this study, we investigated changes in the viscoelasticity of mouse ovarian surface epithelial (MOSE) cells, a mouse model for progressive ovarian cancer. We demonstrate that the elasticity of late-stage MOSE cells (0.549 ± 0.281 kPa) were significantly less than that of their early-stage counterparts (1.097 ± 0.632 kPa). Apparent cell viscosity also decreased significantly from early (144.7 ± 102.4 Pa-s) to late stage (50.74 ± 29.72 Pa-s). This indicates that ovarian cells are stiffer and more viscous when they are benign. The increase in cell deformability directly correlates with the progression of a transformed phenotype from a nontumorigenic, benign cell to a tumorigenic, malignant one. The decrease in the level of actin in the cytoskeleton and its organization is directly associated with the changes in cell biomechanical property. FROM THE CLINICAL EDITOR The authors have investigated changes in the viscoelasticity of mouse ovarian surface epithelial (MOSE) cells and demonstrated that ovarian cells are stiffer and more viscous when they are benign.

High-Speed MEMS-Based Gas Chromatography

This paper reports microfabricated silicon-glass separation columns for high-speed micro gas chromatography (muGC) systems. The microfabricated columns are integrated with resistive heaters and temperatures sensors and capacitive pressure sensors to allow temperature and pressure programming and flow control and to achieve reproducible separations in a muGC system. These 25-cm-long, 150-mum-wide, and 250-mum-deep columns are fabricated on a 1.2-cm square die using a silicon-on-glass dissolved wafer process. Programmed with temperature ramps of 10 degC/s, the low-mass columns separate eleven-component gaseous mixtures in less than 10 s, including alkanes from C5 to C16 and simulants for C-4, TNT, sarin, and mustard gas. When used in arrayed architectures, these MEMS columns should allow high-speed analysis without sacrificing separation efficiency

Design, Modeling, and Fabrication of MEMS-Based Multicapillary Gas Chromatographic Columns

This paper describes different approaches to achieve high-performance microfabricated silicon-glass separation columns for microgas chromatography systems. The capillary width effect on the separation performance has been studied by characterization of 250-, 125-, 50-, and 25-¿m -wide single-capillary columns (SCCs) fabricated on a 10 × 8 mm2 die. The highest plate number (12 500/m), reported to date for MEMS-based silicon-glass columns, has been achieved by 25-¿m-wide columns coated by a thin layer of polydimethylsiloxane stationary phase using static coating technique. To address the low sample capacity of these narrow columns, this paper presents the first generation of MEMS-based ¿multicapillary¿ columns (MCCs) consisting of a bundle of narrow-width rectangular capillaries working in parallel. The theoretical model for the height-equivalent-to-a-theoretical-plate (HETP) of rectangular MCCs has been developed, which relates the HETP to the discrepancies of the widths and depths of the capillaries in the bundle. Two-, four-, and eight-capillary MCCs have been designed and fabricated to justify the separation ability of these columns. These MCCs capable of multicomponent gas separation provide a sample capacity as large as 200 ng compared to 5.5 ng for 25-¿m-wide SCCs.

The cytoskeletal organization of breast carcinoma and fibroblast cells inside three dimensional (3-D) isotropic silicon microstructures

Studying the cytoskeletal organization as cells interact in their local microenvironment is interest of biological science, tissue engineering and cancer diagnosis applications. Herein, we describe the behavior of cell lines obtained from metastatic breast tumor pleural effusions (MDA-MB-231), normal fibrocystic mammary epithelium (MCF10A), and HS68 normal fibroblasts inside three dimensional (3-D) isotropic silicon microstructures fabricated by a single-mask, single-isotropic-etch process. We report differences in adhesion, mechanism of force balance within the cytoskeleton, and deformability among these cell types inside the 3-D microenvironment. HS68 fibroblasts typically stretched and formed vinculin-rich focal adhesions at anchor sites inside the etched cavities. In contrast, MCF10A and MDA-MB-231 cells adopted the curved surfaces of isotropic microstructures and exhibited more diffuse vinculin cytoplasmic staining in addition to vinculin localized in focal adhesions. The measurement of cells elasticity using atomic force microscopy (AFM) indentation revealed that HS68 cells are significantly stiffer (p < 0.0001) than MCF10A and MDA-MB-231 cells. Upon microtubule disruption with nocodazole, fibroblasts no longer stretched, but adhesion of MCF10A and MDA-MB-231 within the etched features remained unaltered. Our findings are consistent with tensegrity theory. The 3-D microstructures have the potential to probe cytoskeletal-based differences between healthy and diseased cells that can provide biomarkers for diagnostics purposes.

Evaluation of the influence of growth medium composition on cell elasticity

Recently, there has been an increasing interest in using the biomechanical properties of cells as biomarkers to discriminate between normal and cancerous cells. However, few investigators have considered the influence of the growth medium composition when evaluating the biomechanical properties of the normal and diseased cells. In this study, we investigated the variation in Youngs modulus of non-malignant MCF10A and malignant MDA-MB-231 breast cells seeded in five different growth media under controlled experimental conditions. The average Youngs modulus of MDA-MB-231 cells was significantly lower (p<0.0001) than the mean Youngs modulus of MCF10A cells when compared in identical medium compositions. However, we found that growth medium composition affected the elasticity of MCF10A and MDA-MB-231 cells. The average Youngs modulus of both cell lines decreased by 10-18% when the serum was reduced from 10% to 5% and upon addition of epidermal growth factor (EGF, 20 ng/ml) to the medium. Though these elasticity changes might have some biological impact, none was statistically significant. However, the elasticity of MCF10A was significantly more responsive than MDA-MB-231 cells to the medium composition supplemented with EGF, cholera toxin (CT), insulin (INS) and hydrocortisone (HC), which are recommended for routine cultivation of MCF10A cells (M5). MCF10A cells were significantly softer (p<0.002) when grown in medium M5 compared to a standard MDA-MB-231 medium (M1). The investigation of the effects of culture medium composition on the elastic properties of cells highlights the need to take these effects into consideration when interpreting elasticity measurements in cells grown in different media.

Low-Mass PECVD Oxynitride Gas Chromatographic Columns

This paper describes the realization of low-power micro gas chromatography columns for portable gas analysis systems. The columns are fabricated using complimentary metal-oxide-semiconductor-compatible buried-channel plasma- enhanced chemical vapor deposition oxynitride films that have nearly zero stress at room temperature, high deposition rate (~1 mum/min), high etch rate selectivity (~1:80), low thermal conductivity (< 5 W/mdegC), and low thermal stress (< 140 kPa/degC). The buried channel process utilizes these films to form 25-cm-long 65-mum-ID semicircular columns on a 6-mm-square chip. With more than 5000 theoretical plates, these columns separate multicomponent gas mixtures with performance comparable to that of commercial fused silica capillary columns. The columns are capable of multisecond analyses when integrated with low-dead-volume injectors and dissipate less than 10 mW at 150degC in vacuum.

MEMS-Based Selective Preconcentration of Trace Level Breath Analytes

This paper presents high-performance micropreconcentrators (muPCs) aimed at breath analysis and a method for eliminating unwanted species from breath samples by using a two-step preconcentration procedure. The muPC consists of embedded high aspect-ratio three-dimensional (3-D) micro pillars coated with an adsorbent polymer. The silicon-glass die has outer dimensions of 7 mm times 7 mm, total inner surface area of ~ 10 m2, and a total inner volume of ~ 6.5 muL. The muPC has on-chip thermal desorption capability and comprises more than 3500 micro pillars with dimensions of 30 mum times 120 mum times 240 mum. The preconcentration factor of the presented muPCs was measured to be above 10 000. Results showed the possibility of selective preconcentration by cascading multiple muPCs with temperature and flow control. The work presented here has profound implications for handheld point-of-care breath analysis instrumentation by first concentrating trace levels of VOCs found in human breath undergoing anesthesia such as n-decane (C10), n-dodecane (C12), 2,6-diisopropylphenol (Propofol), n-tetradecane (C14), and n-hexadecane (C16). Second, it succeeded in eliminating water-like solvent (1-propanol) from the sample to be analyzed. Third, it selectively preconcentrated target compound such as Propofol which is used for medical procedures. The relative concentration of Propofol to C14 was changed from 50% (with one muPC ) to 99.8% (with cascaded muPC). The water-like solvent was also eliminated by 99.9%.

Two-Port Static Coated Micro Gas Chromatography Column With an Embedded Thermal Conductivity Detector

This paper reports a microfabricated 2×4 cm gas chromatography chip to separate and detect gases in a two-port structure by embedding a microthermal conductivity detector (μTCD) within a separation column. A circular on-chip heater is placed on the backside of the monolithic device enabling temperature programming and consequently faster analysis of the heavier components. A unique process enhanced by reactive ion etching lag (RIE lag) is used to achieve multiple etch depths in silicon and restrict the process flow to just three masks. The silicon substrate contains the separation column, the heater, and the tunnels for the TCD electric feed throughs. A Pyrex wafer containing the TCD elements is anodically bonded to the silicon substrate to seal the structure. Performance of a standalone μTCD fabricated in the same process and integrated in a hybrid fashion is also described. The single-chip design demonstrates successful separation and identification of multi-component gas mixtures with a performance comparable to that obtained through a flame ionization detector connected in series. Further, on-chip temperature programming capability was utilized to elevate the column temperature to 75°C to exhibit analysis in less than a minute.

Highly Stable Surface Functionalization of Microgas Chromatography Columns Using Layer-by-Layer Self-Assembly of Silica Nanoparticles

A controllable and high-yield surface functionalization of silicon microchannels using layer-by-layer (LbL) self-assembly of SiO2 nanoparticles (SNPs) is presented. The application of SNPs (45 nm average diameter) coating as a stationary phase for chromatographic separation is also demonstrated with surface functionalization using chloroalkylsilanes. This method facilitates a simple, low-cost, and parallel processing scheme that also provides homogeneous and stable nanoparticle-based stationary phases with ease of control over the coating thickness. The SNP-functionalized microfabricated columns with either single capillary channels (1 m long, 150 μm wide, 240 μm deep) or very narrow multicapillary channels (25 cm long, 30 μm wide, 240 μm deep, 16 parallel channels) successfully separated a multicomponent gas mixture with a wide range of boiling points with high reproducibility.