Karan V. I. S. Kaler

Continuous dielectrophoretic cell separation microfluidic device

We present a prototype microfluidic device developed for the continuous dielectrophoretic (DEP) fractionation and purification of sample suspensions of biological cells. The device integrates three fully functional and distinct units consisting of an injector, a fractionation region, and two outlets. In the sheath and sample injection ports, the cell sample are hydrodynamically focused into a stream of controlled width; in the DEP fractionation region, a specially shaped nonuniform (isomotive) electric field is synthesized and employed to facilitate the separation, and the sorted cells are then delivered to two sample collection ports. The microfluidic behavior of the injector region was simulated and then experimentally verified. The operation and performance of the device was evaluated using yeast cells as model biological particles. Issues relating to the fabrication and operation of the device are discussed in detail. Such a device takes a significant step towards an integrated lab-on-a-chip device, which could interface/integrate to a number of other on-chip components for the device to undertake the whole laboratory procedure.

Ingestible Capsule for Impedance and pH Monitoring in the Esophagus

Twenty-four-hour ambulatory pH monitoring is an essential tool for diagnosing gastroesophageal reflux disease (GERD). Simultaneous impedance and pH monitoring of the esophagus improves the detection and characterization of GERD. Conventional catheter-based monitoring systems are uncomfortable and interfere with the normal activity of the patient. To overcome these disadvantages, different wireless esophageal monitoring systems have been proposed. A capsule containing sensors for impedance and pH monitoring with wireless communication capabilities is presented. A low cost miniature microcontroller was utilized for interfacing between the sensors and a wireless transmitter. The microcontroller program allowed efficient management of the electric power provided by a 3-V battery. Magnetic holding is proposed as an alternative to surgical affixation of the monitoring capsule. Permanent neodymium magnets separated by 27 cm successfully held the capsule in a test tube. Experimental results demonstrated that friction force can aid magnetic holding to overcome peristalsis. The proposed design efficiently detected acid and nonacid reflux. More research regarding the holding method and capsule packaging are necessary to optimize the mechanical performance of the proposed design in order to facilitate clinical testing on human subjects.

A novel current-mode instrumentation amplifier based on operational floating current conveyor

This paper presents a novel current-mode instrumentation amplifier (CMIA) that utilizes an operational floating current conveyor (OFCC) as a basic building block. The OFCC, as a current-mode device, shows flexible properties with respect to other current- or voltage-mode circuits. The advantages of the proposed CMIA are threefold. First, it offers a higher differential gain and a bandwidth that is independent of gain, unlike a traditional voltage-mode instrumentation amplifier. Second, it maintains a high common-mode rejection ratio (CMRR) without requiring matched resistors, and finally, the proposed CMIA circuit offers a significant improvement in accuracy compared to other current-mode instrumentation amplifiers based on the current conveyor. The proposed CMIA has been analyzed, simulated, and experimentally tested. The experimental results verify that the proposed CMIA outperforms existing CMIAs in terms of the number of basic building blocks used, differential gain, and CMRR.

Hybrid Integration of an Active Pixel Sensor and Microfluidics for Cytometry on a Chip

Reported are motivations and approaches for the integration of custom sensors with microfluidic devices for cytometry on a chip and related fluid metering applications. To demonstrate, details of a digital 16-element mixed-signal CMOS active pixel optical sensor with adaptive spatial filtering is first described. The 0.18-mum CMOS fabricated sensor is then shown coupled to a microfluidic channel via a polymer encapsulated chip-on-board approach as well as a preferred flip-chip-on-glass hybrid integration approach. However, both approaches discussed possess attributes that are well suited for reliable high-volume production. Utilizing these two disparate assembly topologies, the intelligent sensors general behavior, optical input dynamic range, and near-field sensitivity to polymer beads being transported in a microfluidic channel is explored. The findings suggest that discrete near-field sensor integration with microfluidics is a well-positioned integration approach for helping to obviate the need for precision analog-to-digital conversion, optical fiber microchannel coupling, and conventional microscopy for a set of relevant micro total analysis system applications. By opting instead for a hybrid multichip module approach to system integration, this study marks a slight departure in strategy relative to many common monolithic system-on-chip integration efforts

Microfluidic Device for Dielectrophoresis Manipulation and Electrodisruption of Respiratory Pathogen Bordetella pertussis

A miniaturized microfluidic device was developed to facilitate electromanipulation of bacterial respiratory pathogens. The device comprises a microchip with circular aluminum electrodes patterned on glass, which is housed in a microfluidic system fabricated utilizing polydimethylsiloxane. The device provides sample preparation capability by exploiting positive dielectrophoresis (DEP) in conjunction with pulsed voltage for manipulation and disruption of Bordetella pertussis bacterial cells. Positive DEP capture of B. pertussis was successfully demonstrated utilizing 10 Vrms and 1 MHz ac fields. Application of dc pulses (300 V amplitude and 50 mu s pulsewidth applied 1 s apart) across the aluminum electrodes resulted in electrodisruption and lysis of B. pertussis bacterial cells. Real-time polymerase chain reaction, a 23 factorial experimental design and transmission electron microscopy were used to evaluate bacterial cell manipulation and factors affecting bacterial cell disruption. The main factors affecting bacterial cell disruption were electric field strength, the electrical conductivity of the cell suspension sample, and the combined effect of number of pulses and sample conductivity. The bacterial deoxyribonucleic acid target remained undamaged as a result of DEP and cell lysis experimentation. Our findings suggest that a simple miniaturized microfluidic device can achieve important steps in sample preparation on-chip involving respiratory bacterial pathogens.

Liquid dielectrophoresis and surface microfluidics.

Liquid dielectrophoresis (L-DEP), when deployed at microscopic scales on top of hydrophobic surfaces, offers novel ways of rapid and automated manipulation of very small amounts of polar aqueous samples for microfluidic applications and development of laboratory-on-a-chip devices. In this article we highlight some of the more recent developments and applications of L-DEP in handling and processing of various types of aqueous samples and reagents of biological relevance including emulsions using such microchip based surface microfluidic (SMF) devices. We highlighted the utility of these devices for on-chip bioassays including nucleic acid analysis. Furthermore, the parallel sample processing capabilities of these SMF devices together with suitable on- or off-chip detection capabilities suggest numerous applications and utility in conducting automated multiplexed assays, a capability much sought after in the high throughput diagnostic and screening assays.

Dynamic Dielectrophoretic Levitation of Living Individual Cells

The levitation of lone live cells by means of dielectrophorectic force provides a means of determining the relative polarization of the cells and their aqueous support medium. When done over a range of frequencies, a spectrum of dielectric (polarization) responses is obtained which serves to characterize a single living cell. In this manner, individual cells of several microorganisms, Saccharomyces cerevisiae and Netrium digitus, were investigated in the frequency range 102-106 Hz. These and related prior studies showed that the positive dielectrophoresis, i.e., where the suspended particle has a greater net polarization than the suspending medium, can be used to show subtle differences between species and even between cells of the same culture.

Quadrupole levitation of microscopic dielectric particles

Abstract Planar quadrupole microelectrodes, fabricated using surface micromachining, have been successfully used to achieve passive levitation of biological cells and other microscopic inorganic particles. To explain certain experimental findings, namely the “size effect”, a simple point charge quadrupole model was invoked to explain qualitatively the experimental observations. Subsequently, a more generalized multipolar theory was formulated to handle such higher-order multipolar effects. In this paper, we examine the salient properties of a practical planar quadrupole electrode structure as predicted by multipolar theory. The analytical data, obtained from multipolar theory is compared with the numerical modeling results form a boundary element simulation package and the levitation data of microscopic Spheriglass® and polymethylmethacrylate particles. The numerical simulation results and the levitation data are both consistent with and in good agreement with the predictions of multipolar theory.

Droplet Microfluidics for Chip-Based Diagnostics

Droplet microfluidics (DMF) is a fluidic handling technology that enables precision control over dispensing and subsequent manipulation of droplets in the volume range of microliters to picoliters, on a micro-fabricated device. There are several different droplet actuation methods, all of which can generate external stimuli, to either actively or passively control the shape and positioning of fluidic droplets over patterned substrates. In this review article, we focus on the operation and utility of electro-actuation-based DMF devices, which utilize one or more micro-/nano-patterned substrates to facilitate electric field-based handling of chemical and/or biological samples. The underlying theory of DMF actuations, device fabrication methods and integration of optical and opto-electronic detectors is discussed in this review. Example applications of such electro-actuation-based DMF devices have also been included, illustrating the various actuation methods and their utility in conducting chip-based laboratory and clinical diagnostic assays.

Multiplex, Quantitative, Reverse Transcription PCR Detection of Influenza Viruses Using Droplet Microfluidic Technology

Quantitative, reverse transcription, polymerase chain reaction (qRT-PCR) is facilitated by leveraging droplet microfluidic (DMF) system, which due to its precision dispensing and sample handling capabilities at microliter and lower volumes has emerged as a popular method for miniaturization of the PCR platform. This work substantially improves and extends the functional capabilities of our previously demonstrated single qRT-PCR micro-chip, which utilized a combination of electrostatic and electrowetting droplet actuation. In the reported work we illustrate a spatially multiplexed micro-device that is capable of conducting up to eight parallel, real-time PCR reactions per usage, with adjustable control on the PCR thermal cycling parameters (both process time and temperature set-points). This micro-device has been utilized to detect and quantify the presence of two clinically relevant respiratory viruses, Influenza A and Influenza B, in human samples (nasopharyngeal swabs, throat swabs). The device performed accurate detection and quantification of the two respiratory viruses, over several orders of RNA copy counts, in unknown (blind) panels of extracted patient samples with acceptably high PCR efficiency (>94%). The multi-stage qRT-PCR assays on eight panel patient samples were accomplished within 35–40 min, with a detection limit for the target Influenza virus RNAs estimated to be less than 10 RNA copies per reaction.