Jaesung Jang

Theoretical and experimental study of MHD (magnetohydrodynamic) micropump

This paper presents a novel micropump of which pumping mechanism is based upon magnetohydrodynamic (MHD) principles. MHD is the study of flow of electrically conducting liquids in electric and magnetic fields. Lorentz force is the pumping source of conductive, aqueous solutions in the MHD micropump. Conducting fluid in the microchannel of the MHD micropump is driven by Lorentz force in the direction perpendicular to both magnetic and electric fields. The performance of the micropump is obtained by measuring the pressure head difference and flow rate as the applied voltage changes from 10 to 60 VDC at 0.19 and 0.44 Tesla (T). The pressure head difference is 18 mm at 38 mA and the flow rate is 63 μl/min at 1.8 mA when the inside diameter of inlet/outlet tube is 2 mm and the magnetic flux density is 0.44 T. Bubble generation by the electrolysis of the conducting liquid can be observed. The performance of the MHD micropump obtained theoretically in single phase is compared with the experimental results.

Real-time detection of airborne viruses on a mass-sensitive device

We present real-time detection of airborne Vaccinia viruses using quartz crystal microbalance (QCM) in an integrated manner. Vaccinia viruses were aerosolized and neutralized using an electrospray aerosol generator, transported into the QCM chamber, and captured by a QCM crystal. The capture of the viruses on the QCM crystal resulted in frequency shifts proportional to the number of viruses. The capture rate varied linearly with the concentration of initial virus suspensions (8.5x10(8)-8.5x10(10) particlesml) at flow rates of 2.0 and 1.1 lmin. This work demonstrates the general potential of mass sensitive detection of nanoscale biological entities in air.

Single-walled carbon nanotube based transparent immunosensor for detection of a prostate cancer biomarker osteopontin

Osteopontin (OPN) is involved in almost all steps of cancer development, and it is being investigated as a potential biomarker for a diagnosis and prognosis of prostate cancer. Here, we report a label-free, highly sensitive and transparent immunosensor based on single-walled carbon nanotubes (SWCNTs) for detection of OPN. A high density of COOH functionalized SWCNTs was deposited between two gold/indium tin oxide electrodes on a glass substrate by dielectrophoresis. Monoclonal antibodies specific to OPN were covalently immobilized on the SWCNTs. Relative resistance change of the immunosensors was measured as the concentration of OPN in phosphate buffer saline (PBS) and human serum was varied from 1 pg mL(-1) to 1 μg mL(-1) for different channel lengths of 2, 5, and 10 μm, showing a highly linear and reproducible behavior (R(2)>97%). These immunosensors were also specific to OPN against another test protein, bovine serum albumin, PBS and human serum, showing that a limit of detection for OPN was 0.3 pg mL(-1). This highly sensitive and transparent immunosensor has a great potential as a simple point-of-care test kit for various protein biomarkers.

Effective heights and tangential momentum accommodation coefficients of gaseous slip flows in deep reactive ion etching rectangular microchannels

The behavior of a rarefied, compressible flow in long, constant cross section channels provides an opportunity to study complex gas dynamics in a simple geometry that allows analytical solutions. The problem of a rarefied, compressible flow in near unity aspect ratio rectangular cross section channels has been all but ignored despite it being a common flow geometry. We present analytical expressions for the mass flow rate in long, straight and uniform rectangular cross section microchannels in the slip flow regime. Using these analytical expressions, we extract the tangential momentum accommodation coefficient (TMAC) as well as the effective channel dimensions to account for a slight curvature of one of the walls of the rectangle. These expressions are effective in near unity aspect ratio rectangular microchannels made by deep reactive ion etching. The dependence of the flow behavior on the channel height to width aspect ratio is discussed as is the effect of the slight deviation from a rectangular cross section. The obtained TMAC results are consistent with values found by previous researchers using similar materials. Finally, a method of determining TMACs in channels consisting of non-homogenous materials or processing methods is presented.

Rapid electrical immunoassay of the cardiac biomarker troponin I through dielectrophoretic concentration using imbedded electrodes

Rapidity and high sensitivity are critical factors for the diagnoses of heart attacks, and cardiac troponin I (cTnI) is at present a clinical standard for its diagnosis. Here we report a rapid, label-free, and highly sensitive single-walled carbon nanotube (SWCNT) electrical immunosensor, featuring two pairs of electrodes. Two concentration electrodes (gaps: 25 and 80µm) and two detection electrodes (source and drain; gap: 20µm; width: 50µm) were used for dielectrophoretic concentration of cTnI on the SWCNT channels and resistance measurements of the dielectrophoresis (DEP)-concentrated cTnI, respectively. The two concentration electrodes were imbedded between upper and lower dielectric layers, facing each other, underneath the -COOH-functionalized SWCNT channels deposited between the detection electrodes. Therefore, the gap between these imbedded concentration electrodes can be reduced to maximize the electric field intensity for DEP-mediated concentration of cTnI, thereby greatly reducing the detection time (1min) and enhancing the limit of detection (0.7-0.8pgmL(-)(1)). Relative resistance changes of the SWCNTs were measured as cTnI concentration in Tris-Borate-EDTA (TBE; 0.0025×) and human serum diluted 500-fold with 0.0025× TBE decreased from 100ngmL(-)(1) to 1pgmL(-1), and they were shown to be linear with the logarithm of cTnI concentration (R(2)=0.99 and 0.97, respectively). These immunosensors also showed high specificity over another cardiac biomarker, myoglobin, TBE medium (0.0025×), and 500-fold diluted human serum. The DEP-capture of cTnI depended on the frequency of the applied electric field, demonstrating the qualitative nature of the real part of the Clausius-Mossotti factor for cTnI.

Label-free Detection of Influenza Viruses using a Reduced Graphene Oxide-based Electrochemical Immunosensor Integrated with a Microfluidic Platform

Reduced graphene oxide (RGO) has recently gained considerable attention for use in electrochemical biosensing applications due to its outstanding conducting properties and large surface area. This report presents a novel microfluidic chip integrated with an RGO-based electrochemical immunosensor for label-free detection of an influenza virus, H1N1. Three microelectrodes were fabricated on a glass substrate using the photolithographic technique, and the working electrode was functionalized using RGO and monoclonal antibodies specific to the virus. These chips were integrated with polydimethylsiloxane microchannels. Structural and morphological characterizations were performed using X-ray photoelectron spectroscopy and scanning electron microscopy. Electrochemical studies revealed good selectivity and an enhanced detection limit of 0.5 PFU mL−1, where the chronoamperometric current increased linearly with H1N1 virus concentration within the range of 1 to 104 PFU mL−1 (R2 = 0.99). This microfluidic immunosensor can provide a promising platform for effective detection of biomolecules using minute samples.

Gas-phase removal of biofilms from various surfaces using carbon dioxide aerosols

The present study evaluated the removal of Escherichia coli XL1-blue biofilms using periodic jets of carbon dioxide aerosols (a mixture of solid and gaseous CO2) with nitrogen gas. The aerosols were generated by the adiabatic expansion of high-pressure CO2 gas through a nozzle and used to remove air-dried biofilms. The areas of the biofilms were measured from scanning electron micrographs before and after applying the aerosols. The removal efficiency of the aerosol treatment was measured with various air-drying times of the biofilms before the treatment, surface materials, and durations of CO2 aerosols in each 8-s aerosol–nitrogen cleaning cycle. Nearly 100% of the fresh biofilms were removed from the various surfaces very reliably within 90 s. This technique can be useful for removing unsaturated biofilms on solid surfaces and has potential applications for cleaning bio-contaminated surfaces.

Effects of inlet/outlet configurations on the electrostatic capture of airborne nanoparticles and viruses

Abstract Motivated by capture and detection of airborne biological agents in real time with a cantilever biosensor without introducing the agents into liquids, we present the effects of inlet/outlet configurations of a homemade particle collector on the electrostatic capture of airborne 100 nm diameter nanoparticles under swirling gas flows. This particle collector has three different inlet/outlet configurations: forward inlet/outlet (FO), backward inlet/outlet (BO) and straight inlet/outlet (SO) configurations. We also present the electrostatic capture of Vaccinia viruses using the same particle collector and compare these virus measurements with the nanoparticle cases. The most particles were collected in the FO configuration. The numbers of particles captured in the BO and SO configurations were close within their standard deviations. For all the three configurations tested, the number of particles captured in the center electrode C was much smaller than those captured in the other electrodes at a flow rate of 1.1 l min−1 and an applied potential of 2 kV. Using a commercial CFD code FLUENT, we also simulated the effects of the three inlet/outlet configurations on the particle capture in terms of particle trajectories, velocities and travel times. This simulation was in a good agreement with measurements that the FO configuration is the most favorable to particle capture among the tested configurations at a flow rate of 1.1 l min−1. The effects of particle diameters on the capture will also be discussed. This collector can be used for real-time monitoring of bioaerosols along with cantilever biosensors.

Gaseous slip flow analysis of a micromachined flow sensor for ultra small flow applications

The velocity slip of a fluid at a wall is one of the most typical phenomena in microscale gas flows. This paper presents a flow analysis considering the velocity slip in a capacitive micro gas flow sensor based on pressure difference measurements along a microchannel. The tangential momentum accommodation coefficient (TMAC) measurements of a particular channel wall in planar microchannels will be presented while the previous micro gas flow studies have been based on the same TMACs on both walls. The sensors consist of a pair of capacitive pressure sensors, inlet/outlet and a microchannel. The main microchannel is 128.0 µm wide, 4.64 µm deep and 5680 µm long, and operated under nearly atmospheric conditions where the outlet Knudsen number is 0.0137. The sensor was fabricated using silicon wet etching, ultrasonic drilling, deep reactive ion etching (DRIE) and anodic bonding. The capacitance change of the sensor and the mass flow rate of nitrogen were measured as the inlet-to-outlet pressure ratio was varied from 1.00 to 1.24. The measured maximum mass flow rate was 3.86 × 10 −10 kg s −1 (0.019 sccm) at the highest pressure ratio tested. As the pressure difference increased, both the capacitance of the differential pressure sensor and the flow rate through the main microchannel increased. The laminar friction constant f · Re, an important consideration in sensor design, varied from the incompressible no-slip case and the mass sensitivity and resolution of this sensor were discussed. Using the current slip flow formulae, a microchannel with much smaller mass flow rates can be designed at the same pressure ratios.

A capacitive micro gas flow sensor based on slip flow

This paper presents a capacitive pressure-based micro gas flow sensor with slip flow analyses considering velocity slip at the wall. The sensor consists of a pair of capacitors for measuring pressure difference between the inlet and outlet and absolute pressure at the outlet, inlet/outlet reservoirs, and the main microchannel causing pressure difference. The main microchannel is 128.0 /spl mu/m wide, 4.64 /spl mu/m deep, and 5680 /spl mu/m long, where the outlet Knudsen number is 0.0137. The sensor was fabricated using wet etching, ultrasonic drilling, Deep Reactive Ion Etching (RIE) and anodic bonding. The capacitance change of the sensor and the mass flow rate of nitrogen were measured as the inlet to outlet pressure ratio increased up to 1.24. With the increasing pressure difference, the capacitance change of the differential pressure sensor and flow rates through the main microchannel increases. The sensitivity of the sensor will also be discussed.