Thanh Cong Nguyen

Modeling and Estimating Simulated DNA Nanopore Translocation Signals

Solid-state nanopores have been proposed for rapid and inexpensive deoxyribonucleic acid (DNA) sequencing and analysis. This technology is primarily based on characterizing the ionic current flowing through the pore as DNA translocates from one side of the pore to the other side under the influence of an electric field. The magnitude of the DNA-induced current blockade is an important analytical feature for these applications. However, it remains a challenging task to accurately determine the ionic current levels due to small signal-to-noise ratios. In order to facilitate reliable analysis it is necessary to understand the noise statistics and develop effective signal estimation techniques. In this paper, we conduct a molecular dynamics simulation of DNA translocations through a solid-state nanopore and reveal that the simulated ionic current signals contain both thermal and shot noise. We then develop a model for these signals and propose a maximum likelihood estimator (MLE) for estimating the ionic current levels. We show that the MLE has the potential to significantly outperform the classic sample mean estimator.

Enhanced thermoelectric performance of graphene nanoribbon-based devices

There have been numerous theoretical studies on exciting thermoelectric properties of graphene nano-ribbons (GNRs); however, most of these studies are mainly based on simulations. In this work, we measure and characterize the thermoelectric properties of GNRs and compare the results with theoretical predictions. Our experimental results verify that nano-structuring and patterning graphene into nano-ribbons significantly enhance its thermoelectric power, confirming previous predictions. Although patterning results in lower conductance (G), the overall power factor (S2G) increases for nanoribbons. We demonstrate that edge roughness plays an important role in achieving such an enhanced performance and support it through first principles simulations. We show that uncontrolled edge roughness, which is considered detrimental in GNR-based electronic devices, leads to enhanced thermoelectric performance of GNR-based thermoelectric devices. The result validates previously reported theoretical studies of GNRs and d...

High frequency characterization of graphene nanoribbon interconnects

Interconnects and nanoscale transmission lines are critical components in the design of nanoelectronic systems. In this letter, we study the high frequency characteristics of chemical vapor deposition (CVD) graphene nanoribbon (GNR) interconnects and radio frequency propagation in GNRs embedded in a coplanar waveguide structure up to 20 GHz. An equivalent transmission line model is proposed to characterize the GNRs in high frequency regime. The strong agreement between fitting circuit parameters and measured data suggests that our model can be used in the design of nanoscale circuits in which GNRs are used to interconnect elements in the circuits. The fabricated GNRs show fairly constant characteristic impedance at high frequencies which could be useful for radio frequency interconnect applications. Our study provides an insight into microwave behavior of GNRs for developing high speed graphene devices.

Environmentally friendly power generator based on moving liquid dielectric and double layer effect.

An electrostatic power generator converts mechanical energy to electrical energy by utilising the principle of variable capacitance. This change in capacitance is usually achieved by varying the gap or overlap between two parallel metallic plates. This paper proposes a novel electrostatic micro power generator where the change in capacitance is achieved by the movement of an aqueous solution of NaCl. A significant change in capacitance is achieved due to the higher than air dielectric constant of water and the Helmholtz double layer capacitor formed by ion separation at the electrode interfaces. The proposed device has significant advantages over traditional electrostatic devices which include low bias voltage and low mechanical frequency of operation. This is critical if the proposed device is to have utility in harvesting power from the environment. A figure of merit exceeding 10000(108μW)/(mm2HzV2) which is two orders of magnitude greater than previous devices, is demonstrated for a prototype operating at a bias voltage of 1.2 V and a droplet frequency of 6 Hz. Concepts are presented for large scale power harvesting.

GFAP Antibody Detection Using Interdigital Coplanar Waveguide Immunosensor

Glioma is the most common primary brain tumor with its early detection remaining a challenge. Autoantibodies against glial fibrillary acidic protein (GFAP) have shown the highest differential expression compared with the other glioma expressed autoantibodies. In this paper, an immunosensor to detect GFAP antibody levels is developed using an interdigital coplanar waveguide (ID-CPW). The ID-CPW is fabricated on an SiO2/Si substrate with the CPW and inter-digital electrode conducting layers made using Cr/Au. The sensor is functionalized, and protein extracted from astrocytes is immobilized on the surface. Sensitivity and dynamic range are ascertained using varying the concentrations of a commercial, polyclonal antibody to GFAP. The electrical detection of antigen-antibody binding is performed in both dry and wet environments across the 1-25-GHz range. Our results show that the proposed sensor can detect antibodies to GFAP to a minimum concentration of 2.9 pg/ml with a turnaround time in less than 3 h. Our electrical measurements indicate an improved sensitivity compared with the state-of-the-art optical detection methods. The immunosensor, developed to detect antibody against GFAP, is the first to show the applicability in the detection of glioma using the GFAP autoantibodies.

An interdigitated electrode biosensor platform for rapid HLA-B*15: 02 genotyping for prevention of drug hypersensitivity

Prevention of life threatening hypersensitivity reactions to carbamazepine is possible through pre-treatment screening of the associated HLA-B*15:02 risk allele. However, clinical implementation of screening is hindered by the high cost and slow turnaround of conventional HLA typing methods. We have developed an interdigitated electrode (IDE) biosensor platform utilizing loop mediated isothermal amplification (LAMP) that can rapidly detect the HLA-B*15:02 allele. DNA amplification is followed by solid-phase hybridization of LAMP amplicons to a DNA probe immobilized on the IDE sensor surface, resulting in a change in sensor impedance. The testing platform does not require DNA extraction or post-amplification staining, achieving sample-to-answer in 1 h and 20 min. The platform was tested on 27 whole blood samples (14 HLA-B*15:02 positive and 13 negative) with sensitivity of 92.9% and specificity of 84.6% when applying a cutoff of impedance change. Based on these characters the LAMP-IDE platform has potential to be further developed into point-of-care use to help overcome barriers in HLA-B*15:02 screening.

CMOS compatible fabrication process of MEMS resonator for timing reference and sensing application

Frequency reference and timing control devices are ubiquitous in electronic applications. There is at least one resonator required for each of this device. Currently electromechanical resonators such as crystal resonator, ceramic resonator are the ultimate choices. This tendency will probably keep going for many more years. However, current market demands for small size, low power consumption, cheap and reliable products, has divulged many limitations of this type of resonators. They cannot be integrated into standard CMOS (Complement metaloxide- semiconductor) IC (Integrated Circuit) due to material and fabrication process incompatibility. Currently, these devices are off-chip and they require external circuitries to interface with the ICs. This configuration significantly increases the overall size and cost of the entire electronic system. In addition, extra external connection, especially at high frequency, will potentially create negative impacts on the performance of the entire system due to signal degradation and parasitic effects. Furthermore, due to off-chip packaging nature, these devices are quite expensive, particularly for high frequency and high quality factor devices. To address these issues, researchers have been intensively studying on an alternative for type of resonator by utilizing the new emerging MEMS (Micro-electro-mechanical systems) technology. Recent progress in this field has demonstrated a MEMS resonator with resonant frequency of 2.97 GHz and quality factor (measured in vacuum) of 42900. Despite this great achievement, this prototype is still far from being fully integrated into CMOS system due to incompatibility in fabrication process and its high series motional impedance. On the other hand, fully integrated MEMS resonator had been demonstrated but at lower frequency and quality factor. We propose a design and fabrication process for a low cost, high frequency and a high quality MEMS resonator, which can be integrated into a standard CMOS IC. This device is expected to operate in hundreds of Mhz frequency range; quality factor surpasses 10000 and series motional impedance low enough that could be matching into conventional system without enormous effort. This MEMS resonator can be used in the design of many blocks in wireless and RF (Radio Frequency) systems such as low phase noise oscillator, band pass filter, power amplifier and in many sensing application.

Detection of weak nano-biosensor signals corrupted by shot noise

Nano-scale biosensors have been identified as the next generation devices for biological and chemical sensing applications and fast sequencing of the human genome. However, detecting targeted molecules is proven to be a challenging task due to weak signal strengths and strong noises. It is therefore vital to understand the noise statistics and develop effective signal detection techniques in order to facilitate the development of reliable devices. In this paper, we build on molecular dynamics simulation results which reveal that the ionic current signals of DNA translocations through solid-state nanopores include both thermal and shot noise, and develop algorithms for effective detection of these signals. Theoretical and simulation results show that the locally most powerful detector has the potential to significantly outperform the classical matched filter.