J. Darabi

Southern Illinois University Edwardsville, Illinois, United States

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Publications (40)47.83 Total impact

  • S Ghanbari · J Darabi
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    ABSTRACT: In this work, copper micropillars and copper–carbon nanotube (CNT) composite micropillars were fabricated by incorporating an electrodeposition technique with a xurography process. In order to disperse carbon nanotubes in copper–CNTmicropillars, various amounts of CNTs were added to the electroplating bath. Surface morphology and phase characterization of copper micropillars and copper–CNTcomposite micropillars were analyzed by optical microscopy and x-ray diffraction. In addition, the corrosion resistance (Rp) of a bare copper substrate, copper micropillars, and optimum copper–CNTmicropillars were studied by electrochemical impedance spectroscopy (EIS) technique in a 3.5 wt.% sodium chloride. Experimental results yielded a corrosion resistance of 200Ωcm2 for the bare copper substrate, 400Ωcm2 for copper micropillars, and 2550Ωcm2 for copper–CNT micropillars, indicating a significantly higher corrosion resistance for copper–CNTmicropillars due to a lower chemical reactivity and refinement of crystal structure of copper in micropillars.
    No preview · Article · Jul 2015
  • C Hale · J Darabi
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    ABSTRACT: This paper presents a continuous flow microfluidic device for the separation of DNA from blood using magnetophoresis for biological applications and analysis. This microfluidic bio-separation device has several benefits, including decreased sample handling, smaller sample and reagent volumes, faster isolation time, and decreased cost to perform DNA isolation. One of the key features of this device is the use of short-range magnetic field gradients, generated by a micro-patterned nickel array on the bottom surface of the separation channel. In addition, the device utilizes an array of oppositely oriented, external permanent magnets to produce strong long-range field gradients at the interfaces between magnets, further increasing the effectiveness of the device. A comprehensive simulation is performed using COMSOL Multiphysics to study the effect of various parameters on the magnetic flux within the separation channel. Additionally, a microfluidic device is designed, fabricated, and tested to isolate DNA from blood. The results show that the device has the capability of separating DNA from a blood sample with a purity of 1.8 or higher, a yield of up to 33 μg of polymerase chain reaction ready DNA per milliliter of blood, and a volumetric throughput of up to 50 ml/h.
    No preview · Article · Jul 2014 · Biomicrofluidics
  • M. Ghajar · J. Darabi
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    ABSTRACT: This study focuses on the thermal and capillary analysis of a micro loop heat pipe for the thermal management of electronic devices and systems. A model is developed using the principles of thin film evaporation to predict the evaporative heat transfer coefficient in grooved capillary structures. In addition, a micro-flow submodel is developed to compute the dry-out distance in rectangular capillary grooves. These submodels are incorporated into our previously developed system-level loop solver model to simulate the performance of a flat micro loop heat pipe. The integrated model predicts the thermal performance, evaporator surface temperature, and local and average heat transfer coefficients as a function of the applied heat load. The modeling results are verified by comparison with the experimental data for a similar device and a good agreement is obtained.
    No preview · Article · May 2014 · International Journal of Thermal Sciences
  • Jeff Darabi · Chuan Guo
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    ABSTRACT: This paper presents the design, fabrication, and testing of a magnetophoretic bioseparation chip for the rapid isolation and concentration of CD4 + T cells from the peripheral blood. In a departure from conventional magnetic separation techniques, this microfluidic-based bioseperation device has several unique features, including locally engineered magnetic field gradients and a continuous flow with a buffer switching scheme to improve the performance of the separation process. Additionally, the chip is capable of processing significantly smaller sample volumes than conventional methods and sample losses are eliminated due to decreased handling. Furthermore, the possibility of sample-to-sample contamination is reduced with the disposable format. The overall dimensions of the device were 22 mm by 60 mm by 1 mm, approximately the size of a standard microscope slide. The results indicate a cell purity of greater than 95% at a sample flow rate of 50 ml/h and a cell recovery of 81% at a sample flow rate of 10 ml/h. The cell purity was found to increase with increasing the sample flow rate. However, the cell recovery decreases with an increase in the flow rate. A parametric study was also performed to investigate the effects of channel height, substrate thickness, magnetic bead size, and number of beads per cell on the cell separation performance.
    No preview · Article · Sep 2013 · Biomicrofluidics
  • Jeff Darabi
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    ABSTRACT: Magnetic separation is one of the effective ways to separate specific biological entities such as DNA/RNA, bacteria, and cells from their native environment for subsequent downstream analysis. The process involves the labeling of the desired biological entity with magnetic beads followed by separating the tagged entities via a magnetic separation device. In conventional tube-based magnetic separation, magnetically labeled biological entities are retained on the inner wall of the tube by applying an external magnet, while the supernatant is decanted off. Removing the tube from the magnetic field enables resuspension of the target entity. Although widely used, there are limitations to the conventional magnetic separation method. For example, there is a significant sample loss due to multiple sample handling, washing, and transfer. In addition, manual magnetic separation systems are labor intensive and their effectiveness is user-dependent.
    No preview · Conference Paper · Jun 2013
  • Ashis Kumar Sen · Jeff Darabi · Daniel R. Knapp
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    ABSTRACT: This work presents simulation of aerosol formation in electrospray ionization (ESI) using a carbon fiber (CF) emitter. The model predicts droplet fission and trajectories of the droplets in a steady medium, within a monodisperse EHD spray in a Lagrangian framework. The droplet fission is simulated based on the principle of minimum free energy and droplet trajectories are predicted using Lagrangian single-droplet tracking method. The numerical model is validated by comparing model predictions with experimental results. The aerosol formation process using the CF emitter is simulated and results are presented and discussed.
    No preview · Article · Oct 2011 · IEEE Sensors Journal
  • A. K. Sen · J. Darabi · D. R. Knapp
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    ABSTRACT: This work presents simulation of jet break up in electrospray ionization using a microfluidic emitter. The emitter comprises a pointed carbon fiber located coaxial with a fused silica capillary of 360 microns OD and 75 microns ID, with its sharp tip extending 30 microns beyond the capillary terminus. The numerical model employs leaky-dielectric formulations for solving the electrodynamics and volume-of-fluid method for tracking the liquid-air interface. The existing leaky-dielectric model is modified to account for the presence of free charges inside the bulk of the liquid as well as at the interface. A small velocity perturbation is used at the capillary inlet to emulate the natural disturbance necessary for the jet break up. First, the model is validated by comparing model predictions with experimental results for a conventional emitter reported in literature. Then, it is applied to simulate the electrospray performance of the Carbon Fiber (CF) emitter including the Taylor cone and jet break up processes. Model predictions for CF emitter are compared with experimental results in terms of jet-length and current-flow characteristics. The influence of emitter geometry, operating conditions and liquid properties on the electrospray performance are investigated. Droplet diameter is correlated with flow rate and liquid properties and the correlation results are compared with that reported in literature. [DOI: 10.1115/1.4004325]
    No preview · Article · Jul 2011 · Journal of Fluids Engineering
  • Ashis K. Sen · J. Darabi · D. R. Knapp
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    ABSTRACT: A microfabricated fluidic interconnection system for polymer-based microfluidic nebulizer chips is presented and discussed. The new interconnection mechanism can be used to make fluidic connection between external capillary and the polymer microfluidic chip. The connector mechanism was fabricated using a combination of mechanical milling and laser micromachining. Preliminary leakage tests were performed to demonstrate that the interconnection system is leak-free and pressure tests were performed to evaluate the burst pressure (maximum working pressure). The interconnection system has several advantages over commercially available Nanoport™ interconnection system. The new fluidic interconnection system implemented onto a microfluidic nebulizer chip was successfully tested for desorption electrospray ionization mass spectrometry applications. The performance of the chip using the new connector mechanism was excellent demonstrating the usability of the new connector mechanism.
    No preview · Article · Apr 2010 · Microsystem Technologies
  • Source
    A.K. Sen · J Darabi · D.R. Knapp
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    ABSTRACT: This paper presents design, microfabrication, and test of a microfluidic nebulizer chip for desorption electrospray ionization mass spectrometry (DESI-MS) in proteomic analysis. The microfluidic chip is fabricated using cyclic olefin copolymer (COC) substrates. The fluidic channels are thermally embossed onto a base substrate using a nickel master and then a top substrate is thermally bonded to seal the channels. Carbon ink embossed into the top COC substrate is used to established electrical connection between the external power supply and the liquid in the channel. The microfluidic chip to external capillary connection is fabricated using Nanoport() interconnection system. Preliminary leakage test was performed to demonstrate the interconnection system is leak-free and pressure test was performed to evaluate the burst pressure. Finally, the nebulizer chip was used to perform DESI-MS for analyzing peptides (BSA and bradykinin) and reserpine on the nanoporous alumina surface. DESI-MS performance of the microfluidic nebulizer chip is compared with that obtained using a conventional DESI nebulizer.
    Full-text · Article · Apr 2009 · Sensors and Actuators B Chemical
  • A K Sen · R Nayak · J Darabi · D R Knapp
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    ABSTRACT: This paper presents use of a nanoporous alumina surface for desorption electrospray ionization mass spectrometry (DESI MS). The DESI MS performance of the nanoporous alumina surface is compared with that of polymethylmethacrylate (PMMA), polytetrafluroethylene (PTFE) and glass, which are popular surfaces in DESI MS experiments. Optimized operating conditions were determined for each of these surfaces by studying the effects of flow rate, tip to surface and surface to MS capillary distance, and spray angle on the DESI MS performance. The analytes (reserpine and BSA tryptic digest) were analyzed on all the surfaces. The results show that the nanoporous alumina surface offers higher ion intensity and increased peptide detection as compared to the other surfaces. Additionally, comparison of ion intensities obtained from the nanoporus alumina and an alumina film confirms that improved performance is due to the inherent nature of the nanostructured surface. Limits of detection (LODs) were determined for the analytes on all the surfaces. It was observed that the nanoporous alumina surface offers improved limits of detection as compared to other surfaces. Another advantage of the nanoporous alumina surface is that it provides to faster analysis associated with rapid drying of liquid samples on the surface. Additionally, porous alumina surface can be used as a dual ionization platform for combined DESI/LDI analysis for further improved peptide detection in proteomic analysis.
    No preview · Article · Sep 2008 · Biomedical Microdevices
  • Ashis Kumar Sen · Jeff Darabi
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    ABSTRACT: This paper presents a comprehensive numerical study of the performance of a capacitive humidity sensor for heating, ventilation, and air conditioning (HVAC) applications. The proposed sensor comprises a sensing layer sandwiched between an array of top and bottom electrodes. A combination of both parallel plate and interdigitated electrode arrangements is considered to achieve their distinctive advantages. Polyimide is used as the humidity sensing material due to good sensing characteristics and aluminum is used as the electrode material because of the ease of fabrication. A layer of polyimide covers the top electrodes to provide protection from atmospheric contamination thus improving durability. The influence of relative humidity on the dielectric constant of the sensing layer is determined theoretically using the models of Looyenga and Shibata The model is validated by comparing model predictions with experimentally measured data for a previously reported capacitive humidity sensor. The model is then used to simulate and predict the performance of the proposed humidity sensor. The effects of design configuration, sensing layer thickness, electrode polarity, electrode width and thickness, and electrode gap are studied. The influence of operating conditions including relative humidity, temperature and voltage is investigated. Based on the simulation results, the optimum design configuration is identified.
    No preview · Article · May 2008 · IEEE Sensors Journal
  • N. Crews · J. Darabi · P. Voglewede · F. Guo · A. Bayoumi
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    ABSTRACT: As researchers work to develop the “Lab-on-a-Chip” system, dielectrophoresis (DEP) is being examined as a mechanism for the micro-fluidic transport and separation of small biological samples such as cells, proteins, and DNA. Interdigitated electrodes are commonly used within such devices to generate the non-uniform electric fields that induce movement. Among other parameters, the magnitude of the DEP force depends upon the gradient of the square of the electric field that is generated by such electrodes. By understanding the effect that the dimensions of the electrodes have on this quantity, micro-fluidic devices can be designed to produce the most effective dielectrophoretic effect on the biological samples. This article examines the relationship between the geometry of the interdigitated electrodes and the magnitude of the DEP force. This is done by obtaining and analyzing an equation for the gradient of the square of the electric field. The equation is generated by fitting the results of extensive numerical simulations. Although the complete equation introduced in this work is based upon theoretical results, many fundamental portions of the present work agree with accepted experimental results. These verifications are also addressed.
    No preview · Article · Aug 2007 · Sensors and Actuators B Chemical
  • A K Sen · J Darabi
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    ABSTRACT: This paper presents a simulation study of the droplet ejection performance of a thermal inkjet print head. The geometry of the print head comprises a dome-shaped ink chamber, a nozzle guide and a ring-shaped heater integrated on each chamber. The design eliminates direct contact between the heater and the ink, thus minimizing heater burnout. The ink manifold, ink chamber and nozzle are aligned, thus facilitating higher nozzle density. The model simulates thermal bubble dynamics including nucleation and growth of thermal bubbles caused by a thermal pulse. The model was validated by comparing model predictions with experimental results for a previously reported print head design. Then, the model was used to simulate the droplet ejection performance of the proposed inkjet print head. Effects of print head geometry including nozzle diameter, nozzle length, chamber size, heater dimensions and location, thermal conductivity of the passivation layer, operating conditions including total thermal energy and pulse width, properties of the ink including density, viscosity and surface tension on the performance of the inkjet device are investigated. The influence of these parameters on the drop volume and velocity, threshold energy and tail length of the ejected droplets is studied.
    No preview · Article · Jun 2007 · Journal of Micromechanics and Microengineering
  • Ashis K. Sen · Jeff Darabi · Ranu Nayak · Daniel R. Knapp
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    ABSTRACT: Desorption electrospray ionization (DESI) is a technique used for direct sampling of a sample or an analyte deposited on a surface under ambient conditions [1]. In DESI, ionized droplets of a spray are directed towards the sample causing desorption of ions due to exchange of charge and momentum. The resulting ions are carried into an ion trap mass spectrometer and analyzed. DESI was originally demonstrated by Takats et al. [1]. They described the new method and applied the same to analyze various compounds present on a variety of surfaces. Followed by this, several researchers [1–5] have investigated on DESI for a wide range of applications including analysis of pharmaceuticals, explosives detection, natural products discovery and in vivo clinical analysis. Recently, Kauppila et al [5] have introduced porous silicon (pSi) and ultra-thin layer chromatography (UTLC) plates for DESI-MS. Similar or improved sensitivities were obtained with pSi and UTLC surfaces as compared to PMMA and PTFE surfaces. This work presents use of a nanoporous alumina surface [6] for DESI – MS. The DESI – MS performance of nanoporous alumina surface is compared with that of PMMA, which is a popular surface in previous DESI-MS experiments. Optimized operating conditions were determined for the surfaces using BSA tryptic digest as the sample. The results show that the nanoporous alumina surface offers significantly higher ion intensity as compared to the other surfaces.
    No preview · Conference Paper · Jun 2007
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    A. K. Sen · J. Darabi · D. R. Knapp
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    ABSTRACT: In this work, we propose a novel carbon nanofiber (CNF) emitter for electrospray ionization (ESI)–mass spectrometry (MS) applications. The proposed emitter comprises an array of CNFs around the orifice of a microscale capillary. The electrospray ionization process is simulated using a CFD code based on Taylor–Melcher leaky-dielectric formulations for solving the electrohydrodynamics and volume-of-fluid (VOF) method for tracking the interface. The code is validated for a conventional multiple electrospray emitter and then applied to simulate the CNF emitter model. The modeling results show that under steady state condition, individual cone-jets are established around each of the CNFs resulting in an array of electrosprays. The approach being taken to fabricate the CNF emitter is briefly discussed. Effects of geometrical parameters including aspect ratio of CNFs, total number of CNFs and distribution pattern of the CNFs on the electrospray performance are studied. The influence of operating parameters such as flow rate, potential difference and physical properties of the solvent on the electrospray behavior is thoroughly investigated. The spray current, ‘onset’ potential and jet diameter are correlated with total number and distribution of CNFs and physical properties of the liquid. The correlation results are compared with the available results in the literature. Higher spray current and lower jet diameter indicate that the device can perform equivalent to nanospray emitters while using a micro-scale orifice. This allows higher sample throughput and eliminates potential clogging problem inherent in nano-capillaries.
    Full-text · Article · May 2007 · Microfluidics and Nanofluidics
  • A. K. Sen · J. Darabi
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    ABSTRACT: This paper presents numerical investigations of jet breakup in electrospray ionization using a carbon fiber emitter. The emitter has a pointed carbon fiber located coaxial with a fused silica capillary of 360μm OD and 75μm ID, with its tip extending 30 micron beyond the capillary exit. The model employs leaky-dielectric formulations to solve electrodynamics and volume-of-fluid technique for tracking the interface. The existing leaky-dielectric model is modified to consider presence of free charges both in the bulk of the liquid as well as on the interface. A velocity perturbation is used at the capillary inlet to emulate the naturally occurring disturbance necessary for the jet breakup. The model is first validated by comparing the model predictions with experimental results for a conventional emitter. Then, it is used to simulate electrospray performance of the carbon fiber emitter, including the Taylor cone and jet breakup processes. The influence of emitter geometry and operating conditions are thoroughly investigated. The droplet diameter and velocity are correlated with flow rate and the correlation results are compared with that reported in literature.
    No preview · Conference Paper · Jan 2007
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    AK Sen · J Darabi · D R Knapp · J Liu
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    ABSTRACT: A novel microscale emitter employing a pointed carbon fiber (CF) can be used for electrospraying in mass spectrometric (MS) analysis. The carbon fiber is located coaxial with a fused silica capillary tube of 360 µm OD and 75 µm ID with its sharp tip extending 30 µm beyond the tube terminus. The electrospray ionization (ESI) process is simulated using a computational fluid dynamics (CFD) code based on the Taylor–Melcher leaky-dielectric fluid model for solving the electrohydrodynamics and the volume of fluid (VOF) approach for tracking the liquid–gas interface. The CFD code is first validated for a conventional geometry and then used to simulate the CF emitter based ESI model. The simulated current–flow and current–voltage results are in good agreement with experimental results for the CF emitter. The effects of emitter geometry, potential difference, flow rate and the physical properties of the liquid on the electrospray behavior of the CF emitter are thoroughly investigated. The spray current and jet diameter are correlated with the flow rate, potential difference and physical properties of the liquid and the correlation results are quantitatively compared with the results reported in the literature.
    Full-text · Article · Mar 2006 · Journal of Micromechanics and Microengineering
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    J. Darabi · C. Rhodes
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    ABSTRACT: A two-dimensional numerical simulation study has been performed to model an electrohydrodynamic (EHD) micropump. The micropump consists of an array of interdigitated electrodes along the top and bottom of the micropump channel. The focus of the simulations was to study the effects of electrode gap, stage gap, channel height, and applied voltage. The numerical results were first validated with experimental data and then applied to obtain optimum electrode design and pump characteristics curves for geometries of interest. Additionally, the simulation results provide details about the flow behavior of the micropump and clearly capture local flow induced by EHD forces.
    Preview · Article · Feb 2006 · Sensors and Actuators A Physical
  • A. K. Sen · J. Darabi · D. R Knapp
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    ABSTRACT: This paper presents the concept and simulation of a novel multiple electrospray emitters for electrospray ionization mass spectrometric (ESI-MS) applications. The proposed emitter is based on an array of carbon nanofibers (CNF) vertically grown around the orifice of a microscale thermoplastic capillary. The electrospray ionization process is simulated using a CFD code that utilizes Taylor-Melcher leaky-dielectric formulations for the electrohydrodynamics and volume-of-fluid (VOF) method for tracking the interface. The modeling results predict that under steady state conditions, individual cone-jets are established around each of the CNFs resulting in an array of electrosprays. Effects of several design and operational parameters on the electrospray performance are thoroughly investigated. The results of the present study will facilitate design, fabrication and experiments using the CNF emitter. Higher spray current and lower jet diameter indicate that the proposed emitter can perform equivalent to nanospray emitters exhibiting improved MS sensitivity while using a microscale orifice. Use of microscale orifice benefits in terms of higher sample throughput and eliminates potential clogging problem inherent in nanoscale capillaries. Overall, the proposed emitter is believed to be a suitable candidate for ESI-MS applications.
    No preview · Conference Paper · Jan 2006
  • Donald E. Floyd · Mark J. Topolski · Jeff Darabi
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    ABSTRACT: This paper present an analytical and experimental investigation of the performance of metal foams in an impinging flow application. Microstructures of the foam as well as the foam-to-solid braze interface are presented. Aditionally, the effects of brazing procedure on the performance of the heat exchanger are investigated and the results are compared to CFD analysis assuming perfect braze joints. Finally, the results are compared to commercially available micro-channel heat exchangers.
    No preview · Conference Paper · Jan 2006

Publication Stats

559 Citations
47.83 Total Impact Points

Institutions

  • 2013-2014
    • Southern Illinois University Edwardsville
      • Mechanical & Industrial Engineering
      Illinois, United States
  • 2002-2011
    • University of South Carolina
      • Department of Mechanical Engineering
      Columbia, South Carolina, United States
  • 2001
    • Loyola University Maryland
      Baltimore, Maryland, United States
  • 1999-2001
    • University of Maryland, College Park
      • Department of Mechanical Engineering
      Maryland, United States
  • 1995
    • Sharif University of Technology
      Teheran, Tehrān, Iran