Ruiguo Yang

Development of Infrared Detectors Using Single Carbon-Nanotube-Based Field-Effect Transistors

Carbon nanotube is a promising material to fabricate high-performance nanoscale-optoelectronic devices owing to its unique 1-D structure. In particular, different types of carbon-nanotube-infrared detectors have been developed. However, most previous reported carbon-nanotube-IR detectors showed poor device characteristics due to limited understanding of their working principles. In this paper, three types of IR detectors were fabricated using carbon-nanotube field effect transistors (CNTFETs) to investigate their performance: 1) symmetric Au-CNT-Au CNTFET IR detector; 2) symmetric Ag-CNT-Ag CNTFET IR detector; and 3) asymmetric Ag-CNT-Au CNTFET IR detector. The theoretical analyses and experimental results have shown that the IR detector using an individual single-wall carbon nanotube (SWCNT), with asymmetric Ag-CNT-Au CNTFET structure, can suppress dark current and increase photocurrent by electrostatic doping. As a result, an open-circuit voltage of 0.45 V under IR illumination was generated, which is the highest value reported to date for an individual SWCNT-based photodetector. The results reported in this paper have demonstrated that the CNTFET can be used to develop high-performance IR sensors.

Investigation of human keratinocyte cell adhesion using atomic force microscopy

UNLABELLED Desmosomal junctions are specialized structures critical to cellular adhesion within epithelial tissues. Disassembly of these junctions is seen consequent to the development of autoantibodies directed at specific desmosomal proteins in blistering skin diseases such as pemphigus. However, many details regarding cell junction activity under normal physiological and disease conditions remain to be elucidated. Because of their complex structure, desmosomal junctions are not well suited to existing techniques for high-resolution three-dimensional structure-function analyses. Here, atomic force microscopy (AFM) is used for detailed characterization and visualization of the cell junctions of human epithelial cells. We demonstrate the ability to image the detailed three-dimensional structure of the cell junction at high magnification. In addition, the effect of specific antibody binding to desmosomal components of the cell junction is studied in longitudinal analyses before and after antibody treatment. We show that antibodies directed against desmoglein 3 (a major component of the desmosomal structural unit, and the major target of autoantibodies in patients with pemphigus vulgaris) are associated with changes at the cell surface of the human keratinocytes and alterations within keratinocyte intercellular adhesion structures, supporting the assertion that cell structures and junctions are modified by antibody binding. The present study indicates that the molecular structure of gap junctions can be more completely analyzed and characterized by AFM, offering a new technological approach to facilitate a better understanding of disease mechanisms and potentially monitor therapeutic strategies in blistering skin diseases. FROM THE CLINICAL EDITOR Disassembly of desmosomal junctions is seen in blistering skin diseases such as Pemphigus. This present study demonstrates that the molecular structure of gap junctions can be more completely analyzed and characterized by atomic force microscopy.

Development of a miniature self-stabilization jumping robot

We present the design and implementation of a new jumping robot for mobile sensor network. Unlike other jumping robots, the robot is based on a simple two-mass-spring model. After we throw it on ground, it can stabilize itself and then jump once. The detailed mechanism design including the load holding and self-stabilization are presented. Jumping heights and distances with different robot weights are measured and compared with calculated values from the two-mass-spring model.

Infrared Camera Using a Single Nano-Photodetector

Infrared (IR) cameras have versatile applications; however, the low performance and high cost of conventional photodetectors have prevented their widespread utilization in various fields. Nano-materials have recently emerged as possible sensing elements of nano-photodetectors, and have exhibited data that may outperform their conventional counterparts. Carbon nanotube (CNT), a promising nano-material with excellent optical properties, has been employed to develop high performance photodetectors with low noise, tunable bandgap, and noncryogenic cooled operation. However, it is difficult to fabricate a large scale CNT photodetector array that can be integrated into traditional IR camera structures. In order to take advantage of the outstanding performance of the nano-photodetectors and overcome the fabrication difficulties to achieve high resolution and efficient imaging, we present a compressive sensing-based IR camera using a single pixel CNT photodetector. A photonic cavity is developed to integrate with the CNT photodetector so as to increase the absorption area of the device. The camera system uses the CNT photodetector to compressively sample the linear projections of the images onto binary random patterns. Employing the compressive sensing algorithm, high resolution imaging can be achieved with many fewer samples than the original image dimension. The camera is demonstrated effectively in order to observe the dynamic movement of a laser spot. By adaptively adjusting the camera setup, a zooming technique is developed to image small features. To our knowledge, this is the first demonstration of an IR camera using a nano-size photodetector. Our work shows that compressive sensing-based cameras have the potential to complement or selectively replace conventional IR imaging systems.

Characterization of mechanical behavior of an epithelial monolayer in response to epidermal growth factor stimulation

Cell signaling often causes changes in cellular mechanical properties. Knowledge of such changes can ultimately lead to insight into the complex network of cell signaling. In the current study, we employed a combination of atomic force microscopy (AFM) and quartz crystal microbalance with dissipation monitoring (QCM-D) to characterize the mechanical behavior of A431 cells in response to epidermal growth factor receptor (EGFR) signaling. From AFM, which probes the upper portion of an individual cell in a monolayer of cells, we observed increases in energy dissipation, Youngs modulus, and hysteresivity. Increases in hysteresivity imply a shift toward a more fluid-like mechanical ordering state in the bodies of the cells. From QCM-D, which probes the basal area of the monolayer of cells collectively, we observed decreases in energy dissipation factor. This result suggests a shift toward a more solid-like state in the basal areas of the cells. The comparative analysis of these results indicates a regionally specific mechanical behavior of the cell in response to EGFR signaling and suggests a correlation between the time-dependent mechanical responses and the dynamic process of EGFR signaling. This study also demonstrates that a combination of AFM and QCM-D is able to provide a more complete and refined mechanical profile of the cells during cell signaling.

Quantitative Analysis of Human Keratinocyte Cell Elasticity Using Atomic Force Microscopy (AFM)

We present the use of atomic force microscopy (AFM) to visualize and quantify the dynamics of epithelial cell junction interactions under physiological and pathophysiological conditions at the nanoscale. Desmosomal junctions are critical cellular adhesion components within epithelial tissues and blistering skin diseases such as Pemphigus are the result in the disruption of these components. However, these structures are complex and mechanically inhomogeneous, making them difficult to study. The mechanisms of autoantibody mediated keratinocyte disassembly remain largely unknown. Here, we have used AFM technology to image and measure the mechanical properties of living skin epithelial cells in culture. We demonstrate that force measurement data can distinguish cells cultured with and without autoantibody treatment. Our demonstration of the use of AFM for in situ imaging and elasticity measurements at the local, or tissue level opens potential new avenues for the investigation of disease mechanisms and monitoring of therapeutic strategies in blistering skin diseases.

Bionanomanipulation Using Atomic Force Microscopy

This paper explains how an AFM-based nanorobot was developed to visualize and quantify the dynamics of cell proteins interactions under physiological and pathophysiological conditions at the nanoscale. As these events are directly related at the molecular level to the causes of many life-threatening or incurable diseases, the development of an AFM-based nanorobot, which can image and manipulate biological objects at the single molecule level, is a novel approach to reveal disease markers and elucidate the disease mechanisms.

Compressive Feedback-Based Motion Control for Nanomanipulation—Theory and Applications

Conventional scanning probe microscopy (SPM)-based nanomanipulations always have to face scanner accuracy problems such as hysteresis, nonlinearity, and thermal drift. Although some scanners consist of internal position sensors, the sensitivity is not high enough to monitor high-resolution nanomanipulations. Additionally, once the scan size decreases to a nanolevel such as less than 100 nm, the noise brought by sensors is large enough to affect the performance of the closed-loop motion control system. In this paper, a non-vector space control strategy based on compressive feedback is proposed in order to improve the accuracy of SPM-based nanomanipulations. In this approach, local images (or compressive data) are used as both the reference input and feedback for a non-vector space closed-loop controller which considers the local image (or compressive data) as a set. The controller is designed in non-vector space, and it requires no prior information on features or landmarks which are widely used in traditional visual servoing. In this paper, the atomic force microscopy is used as an example of SPM to implement the non-vector space control strategy for nanomanipulations. The motivation of designing such a non-vector space controller is to solve the accuracy problem in nanomanipulation. Without this technique, the SPM-based nanomanipulations, such as nanomeasurement and nanosurgery, are difficult to conduct, with accuracy controlled under several nanometers. In order to illustrate the contributions and potential applications of this non-vector controller, at the end of this paper, an application of carbon nanotube local electrical property characterization based on a non-vector space motion control is shown to clearly verify the concept. Compared with other research in the local electrical property characterization, the non-vector space controller can ensure that the measurement accuracy (position error) is controlled within a few nanometers, which also ensures the reliability of measurement results. Additionally, this non-vector space control method can be implemented into any kind of SPM to realize a real-time control for nanomanipulation such as nanofabrication and nanoassembly.

Cellular biophysical dynamics and ion channel activities detected by AFM-based nanorobotic manipulator in insulinoma β-cells

UNLABELLED Distinct biochemical, electrochemical and electromechanical coupling processes of pancreatic β-cells may well underlie different response patterns of insulin release from glucose and capsaicin stimulation. Intracellular Ca(2+) levels increased rapidly and dose-dependently upon glucose stimulation, accompanied with about threefold rapid increases in cellular stiffness. Subsequently, cellular stiffness diminished rapidly and settled at a value about twofold of the baseline. Capsaicin caused a similar transient increase in intracellular Ca(2+) changes. However, cellular stiffness increased gradually to about twofold until leveling off. The current study characterizes for the first time the biophysical properties underlying glucose-induced biphasic responses of insulin secretion, distinctive from the slow and single-phased stiffness response to capsaicin despite similar changes in intracellular Ca(2+) levels. The integrated AFM nanorobotics and optical investigation enables the fine dissection of mechano-property from ion channel activities in response to specific and non-specific agonist stimulation, providing novel biomechanical markers for the insulin secretion process. FROM THE CLINICAL EDITOR This study characterizes the biophysical properties underlying glucose-induced biphasic responses of insulin secretion. Integrated AFM nanorobotics and optical investigations provided novel biomechanical markers for the insulin secretion process.

Video rate Atomic Force Microscopy (AFM) imaging using compressive sensing

Atomic Force Microscopy (AFM) is a powerful tool for nano-size imaging. The advantage of AFM is that it can get extraordinary high resolution image at atom level. However, AFM obtains the sample topography image through scanning on the top of sample line by line, therefore it takes couples minutes to get an image and this negative point makes it difficult to continuously observe surface change during manipulation. In this paper, a novel approach for compressive sensing based video rate AFM imaging system is proposed. In this method, compressive sensing is used for sampling topography information of sample surface efficiently. Compressive sensing could use fewer measurements for data sensing to recovery the image through image reconstruction algorithm. This technique decreases the scanning time for AFM scanner because of fewer measurements needed. The video rate for this new approach could reach as high as 1.75 seconds per frame.