Pramod K. Singh

All electronic approach for high-throughput cell trapping and lysis with electrical impedance monitoring

We present a portable lab-on-chip device for high-throughput trapping and lysis of single cells with in-situ impedance monitoring in an all-electronic approach. The lab-on-chip device consists of microwell arrays between transparent conducting electrodes within a microfluidic channel to deliver and extract cells using alternating current (AC) dielectrophoresis. Cells are lysed with high efficiency using direct current (DC) electric fields between the electrodes. Results are presented for trapping and lysis of human red blood cells. Impedance spectroscopy is used to estimate the percentage of filled wells with cells and to monitor lysis. The results show impedance between electrodes decreases with increase in the percentage of filled wells with cells and drops to a minimum after lysis. Impedance monitoring provides a reasonably accurate measurement of cell trapping and lysis. Utilizing an all-electronic approach eliminates the need for bulky optical components and cameras for monitoring.

BROADBAND MILLIMETERWAVE METAMATERIAL ABSORBER BASED ON EMBEDDING OF DUAL RESONATORS

Metamaterial based electromagnetic wave absorbers provide perfect absorption only over a narrow bandwidth. In this paper, broadband response is achieved through embedding of one resonator inside another in each unit cell of the metamaterial absorber lattice. These two resonators are oriented in the same direction to achieve reduced coupling between them realizing two absorption frequencies close to each other in order to broaden the efiective bandwidth. The paper presents such an absorber at 77GHz with a bandwidth of 8GHz and peak absorption of greater than 98%. The absorber is fabricated on 125m thin and ∞exible polyimide substrate by patterning gold thin fllm in the shape of two split ring resonators as the metamaterial unit cell. The bandwidth is enhanced by more than a factor of two compared to what could be achieved from a metamaterial with single resonator structure.

Low-Voltage Switchable Microplasma Arrays Generated Using Microwave Resonators

Microplasmas are generated at atmospheric pressure using an array of microstrip resonators and controlled by diode switches. These microplasmas are sustained by continuous microwave power, but can be individually switched on and off by applying +2/-5 VDC to the diodes. Each diode allows the capacitance between the resonator and reference electrode to be switched in or out of the circuit, shifting the resonant frequency and modulating power delivered to the microplasma. We present models of the resonator circuit including plasma loading and demonstrate the circuits efficacy for the addressable control of microplasmas in a five-resonator array.

Three dimensional graphene scaffold for cardiac tissue engineering and in-situ electrical recording

In this paper, we present a three-dimensional graphene foam made of few layers of CVD grown graphene as a scaffold for growing cardiac cells and recording their electrical activity. Our results show that graphene foam not only provides an excellent extra-cellular matrix (ECM) for the culture of such electrogenic cells but also enables recording of its extracellular electrical activity in-situ. Recording is possible due to graphenes excellent conductivity. In this paper, we present our results on the fabrication of the graphene scaffold and initial studies on the culture of cardiac cell lines such as HL-1 and recording of their real-time electrical activity.

Three dimensional graphene transistor for ultra-sensitive pH sensing directly in biological media

In this work, pH sensing directly in biological media using three dimensional liquid gated graphene transistors is presented. The sensor is made of suspended network of graphene coated all around with thin layer of hafnium oxide (HfO2), showing high sensitivity and sensing beyond the Debye-screening limit. The performance of the pH sensor is validated by measuring the pH of isotonic buffered, Dulbeccos phosphate buffered saline (DPBS) solution, and of blood serum derived from Sprague-Dawley rat. The pH sensor shows high sensitivity of 71xa0±xa07xa0mV/pH even in high ionic strength media with molarities as high as 289xa0±xa01xa0mM. High sensitivity of this device is owing to suspension of three dimensional graphene in electrolyte which provides all around liquid gating of graphene, leading to higher electrostatic coupling efficiency of electrolyte to the channel and higher gating control of transistor channel by ions in the electrolyte. Coating graphene with hafnium oxide film (HfO2) provides binding sites for hydrogen ions, which results in higher sensitivity and sensing beyond the Debye-screening limit. The 3D graphene transistor offers the possibility of real-time pH measurement in biological media without the need for desaltation or sample preparation.

Three dimensional monolayer graphene foam for ultra-sensitive pH sensing

In this work, we present liquid gated three-dimensional graphene transistor for pH sensing. The sensor is made of three-dimensional network of graphene coated with hafnium oxide (HfO2) operating as a pH-sensitive liquid gated field effect transistor with super-nerstian sensitivity. We attribute high sensitivity in this device to the coating of HfO2 which provides increased interaction with hydrogen ions in the solution and on the three dimensional foam-like structure of the graphene transistor which provides very high surface-to-volume ratio.

In-Situ Large Area Fabrication of Metamaterials on Arbitrary Substrates Using Paint Process

This paper proposes a novel method to make large area metamaterials on arbitrary planar hard or ∞exible substrates, in-situ. The method is based on painting the desired substrate with metallic and dielectric paints through a patterned stencil mask. We demonstrate this painting approach to fabricate ultra- thin electromagnetic absorbers based on metamaterials at X-band frequencies (8{12GHz) with paper-based stencils, silver ink and latex paint. Measurement results on absorber samples made with this process show absorption of 95%{99% in close agreement with simulation results. The proposed painting approach is a simple low cost additive manufacturing process that can be used to realize metamaterials, frequency selective surfaces, radar absorbers, camou∞age screens, electromagnetic sensors and EMI protection devices.

Active Layer Thickness Effects on the On-State Current and Pulse Measurement at Room Temperature on Deposited Zinc Oxide Thin-Film Transistors

This study reports on the fabrication of thin-film transistors (TFTs) with transparent zinc oxide (ZnO) semiconductors serving as the active channel and silicon dioxide (SiO2) serving as the gate insulator. The ZnO films were deposited by radiofrequency magnetron sputtering at room temperature. Moreover, the effects of channel thickness on the structural and pulse current–voltage characteristics of ZnO TFTs using a bottom gate configuration were investigated. As the channel thickness increased, the crystalline quality and the channel conductance were enhanced. The electrical characteristics of TFTs exhibited field-effect mobilities of 8.36xa0cm2/Vs to 16.40xa0cm2/Vs and on-to-off current ratios of 108 to 107 for ZnO layer thickness of 45xa0nm and 70xa0nm, respectively. The threshold voltage was in the range of 10xa0V to 31xa0V for ZnO layer thicknesses from 35xa0nm to 70xa0nm, respectively. The low deposition and processing temperatures make these TFTs suitable for fabrication on flexible substrates.

Terahertz metamaterials for modulation and detection

This paper reviews recent work in the area of active metamaterials where transistors and circuitry are embedded within metamaterial structures for novel functions. In one function, embedding of psuedomorphic high electron mobility transistor (pHEMT) within the metamaterial resonator allows realization of a terahertz modulator. A variation of this approach utilizes diodes to modulate the metamaterial response between a perfect absorber and a perfect detector. In another function, a transistor based power detector is embedded within each metamaterial resonator for roomtemperature detection of gigahertz (GHz) radiation. The realized platform has the potential for high resolution imaging at the diffraction limit. These functions indicate range of novel devices enabled through heterogeneous integration of semiconductor devices with metamaterials.

A logic-controllable array of high-density microplasmas

Summary form given only. Previously we have demonstrated the technique of generating arrays of microplasmas in small gaps between the ends of microwave resonators and reference electrodes. These arrays are fabricated using micro-milling of standard microwave substrates and typically operated in atmospheric-pressure argon. Here we demonstrate circuits where individual microplasmas can be switched on or off by low-voltage logic signals. Such switchable microplasmas could be of interest as components in novel circuitry and sensing devices or as patterning elements in atmospheric-pressure deposition of thin films. The switches are implemented as diodes connecting the reference electrodes to a ground plane. Reverse-biasing a diode prevents microwave current from flowing through, causing the reference electrode to float and reducing the voltage across the discharge gap below the level that can sustain a microplasma. Inductors act as a microwave block to isolate the logic control from the microwave power. We use an analytical transmission-line model to examine the behavior of the combined resonant and logic circuits, and to estimate the effects of microplasma formation on circuit behavior. This model and experimental evidence suggest the importance of minimizing stray capacitance to ensure full microplasma suppression. The microplasmas themselves are characterized using spectroscopic techniques. Stark broadening measurements show that microplasmas with electron densities in excess of 1014 cm-3 can be fully controlled by logic voltages of +2 / -5 V. In addition, plasma switching speeds are estimated through time-resolved photography using an ICCD camera.