Motivated by previous successes in the development of two-dimensional (2D) based electronic nose, we investigate the potential application of metal-decorated phosphorene-based sensor for detection of formaldehyde using density functional theory (DFT) and nonequilibrium Green’s function (NEGF) methods. The most stable adsorption configurations, adsorption sites, adsorption energies, charge transfer, and electronic properties of formaldehyde on the pristine and Pd-decorated phosphorene are studied. Our results indicate that formaldehyde is chemisorbed on Pd-decorated phosphorene via strong covalent bonds, and quick recovery time (3.58 sec) under UV exposure and at the temperature of 350 K, suggesting its potential application for gas sensors. The results reveal that Pd-decorated phosphorene can detect formaldehyde with high sensitivity of 3.8 times greater than pristine phosphorene. Our results demonstrate the potential application of phosphorene for detection of formaldehyde as an important lung cancer biomarker.
Photomechanics, i.e., the conversion of light into thermal and mechanical work is of significant importance for energy conversion/reconfigurable technologies. Advantages of such photo-thermal mechanisms for transducers include remote energy transfer, remote controllability, control of actuation using number of photons (intensity) and photon energies (wavelength), fast actuation (milliseconds), low signal to noise ratio, high stored elastic strain energy densities with hyperelastic elastomers and scalability at different length scales using batch fabrication and high-volume semiconductor manufacturing. However, only a few materials exist that can convert light into mechanical work. Azobenzene liquid crystal elastomers were one of the first materials to exhibit the photomechanical effect. However, their application required two different light sources for reversible thermal switching (420 nm and 365 nm) between an extended trans and a shorter cis configuration. In this talk, we will cover how light is used with new materials to create the mechanical effect. New nanomaterials, when mixed with polymeric materials, show the unusual photomechanical effect that can be practically harnessed for real-world application. Straining new 2D nanomaterials such as graphene, MoS2 and others creates a new effect called the coupled straintronic photo-thermic effect enables large light absorption and also increase in mechanical effect. The talk will go through an overview of this new and upcoming area of research based on light-matter interaction in 1D and 2D nanomaterial composites.
The ability to convert photons of different wavelength directly into mechanical motion is of significant interest in many energy conversion and reconfigurable technologies. Using few layer 2H-MoS2 nanosheets, layer by layer process of nanocomposite fabrication, and strain engineering, we demonstrate a reversible and chromatic mechanical response in MoS2-nanocomposites between 405 nm to 808 nm with large stress release. The chromatic mechanical response originates from the d orbitals and is related to the strength of the direct exciton resonance A and B of the few layer 2HMoS2 affecting optical absorption and subsequent mechanical response of the nanocomposite. The unique photomechanical response in 2H-MoS2 based nanocomposites is a result of the rich d electron physics not available to nanocomposites based on sp2 bonded graphene and carbon nanotubes, as well as nanocomposite based on metallic nanoparticles. The reversible strain dependent optical absorption suggest applications in broad range of energy conversion technologies.
We present a new method for circulating tumor cell capture based on micro-array isolation from droplets. Called droplet biopsy, our technique uses a 76-element array of carbon nanotube devices functionalized with anti-EpCAM and antiHer2 antibodies for immunocapture of spiked breast cancer cells in the blood. This droplet biopsy chip can enable capture of CTCs based on both positive and negative selection strategy. Negative selection is achieved through depletion of contaminating leukocytes through the differential settling of blood into layers. We report 55%-100% cancer cell capture yield in this first droplet biopsy chip study. The droplet biopsy is an enabling idea where one can capture CTCs based on multiple biomarkers in a single blood sample.
Several high aspect ratio nanostructures have been made by capillary force directed self-assembly including polymeric nanofiber air-bridges, trampoline-like membranes, microsphere-beaded nanofibers, and intermetallic nanoneedles. Arrays of polymer air-bridges form in seconds by simply hand brushing a bead of polymeric liquid over an array of micropillars. The domination of capillary force that is thinning unstable capillary bridges leads to uniform arrays of nanofiber air-bridges. Similarly, arrays of vertically oriented Ag2Ga nanoneedles have been formed by dipping silvercoated arrays of pyramidal silicon into melted gallium. Force-displacement measurements of these structures are presented. These nanostructures, especially when compressively or torsionally buckled, have extremely low stiffnesses, motion due to thermal fluctuations that is relatively easily detected, and the ability to move great distances for very small changes in applied force. Nanofibers with bead-on-a-string structure, where the beads are micron diameter and loaded with magnetic iron oxide (maghemite), are shown to be simply viewable under optical microscopes, have micronewton/ m stiffness, and have ultralow torsional stiffnesses enabling the bead to be rotated numerous revolutions without breaking. Combination of these high aspect ratio structures with stretched elastomers offer interesting possibilities for robotic actuation and locomotion. Polydimethylsiloxane loaded with nanomaterials, e.g. nanotubes, graphene or MoS2, can be efficiently heated with directed light. Heating produces considerable force through the thermoelastic effect, and this force can be used for continuous translation or to trigger reversible elastic buckling of the nanostructures. The remote stimulation of motion with light provides a possible mechanism for producing cooperative behavior between swarms of semiautonomous nanorobots.
By dispersing graphene nanoplatelets (GNPs) within a polydimethylsiloxane matrix, we show that light
absorption by GNPs and subsequent energy transduction to the polymeric chains can be used to controllably produce
significant amounts of motion through entropic elasticity of the pre-strained composite. Using dual actuators, a twoaxis
sub-micron resolution stage was developed, and allowed for two-axis photo-thermal positioning (~100 μm per
axis) with 120 nm resolution (feedback sensor limitation), and ~5 μm s-1 actuation speeds. A PID control loop
automatically stabilizes the stage against thermal drift, as well as random thermal-induced position fluctuations (up
to the bandwidth of the feedback and position sensor).
Detection of circulating tumor cells (CTCs) from patient blood samples offers a desirable alternative to invasive tissue biopsies for screening of malignant carcinomas. A rigorous CTC detection method must identify CTCs from millions of other formed elements in blood and distinguish them from healthy tissue cells also present in the blood. CTCs are known to overexpress surface receptors, many of which aid them in invading other tissue, and these provide an avenue for their detection. We have developed carbon nanotube (CNT) thin film devices to specifically detect these receptors in intact cells. The CNT sidewalls are functionalized with antibodies specific to Epithelial Cell Adhesion Molecule (EpCAM), a marker overexpressed by breast and other carcinomas. Specific binding of EpCAM to anti-EpCAM antibodies causes a change in the local charge environment of the CNT surface which produces a characteristic electrical signal. Two cell lines were tested in the device: MCF7, a mammary adenocarcinoma line which overexpresses EpCAM, and MCF10A, a non-tumorigenic mammary epithelial line which does not. Introduction of MCF7s caused significant changes in the electrical conductance of the devices due to specific binding and associated charge environment change near the CNT sidewalls. Introduction of MCF10A displays a different profile due to purely nonspecific interactions. The profile of specific vs. nonspecific interaction signatures using carbon based devices will guide development of this diagnostic tool towards clinical sample volumes with wide variety of markers.
It is highly likely that future micro and nano-mechanical systems will be powered by light. However, the development of
such micro and nano-mechanical systems is still in its infancy. Potential advantages include remote triggering and
actuation, remote energy transmission, solar energy scavenging for useful work, and wavelength selectivity of actuation.
In recent years, carbon based nano-materials such as carbon nanotubes have shown highly interesting optical to
mechanical energy conversion. The development of optical to mechanical energy transducing mechanisms into practical
applications is still in its infancy. Only a few devices have been reported till date. This paper presents some of the recent
developments in the area of nanotube based photomechanical actuators with emphasis on micro and nanooptomechanical
systems. Devices namely micro-cantilevers for detection of free PSA, micro-grippers for manipulation
of small particles and micro-mirrors for light modulation have been developed that show both translational and
rotational actuation. Finally, integrating nanowires on these platforms could lead to the development of nanooptomechanical
systems. The future research of such systems and how they can play an integral part in electronics,
sensing and actuation by integrating nanotechnology with mechanics, optics and electronics is discussed.o
We describe solid state gas microsensor array technology for real-time, low-cost environmental and industrial monitoring. The four-element, surface-micromachined arrays are designed in CMOS technology and consist of multiple platforms called 'microhotplates.' Each microhotplate can be individually addressed, and includes functionality for rapid control and measurement of sensor temperature and gas-induced changes in a sensing film's electrical properties. The array elements can be tuned for specific analytes, by choice of sensing material and the temperature-programs applied, in order to better meet the needs of a particular application. Tin oxide was used as the base sensing material for microhotplates used in these studies. Tin oxide is grown selectively on each individual element within the arrays using a chemical vapor deposition process involving thermal decomposition of tetramethyltin in an argon and oxygen ambient. Catalytic additives, such as Pt, Pd and Cu are surface-dispersed to make the films more selective and sensitive. Detection capabilities for the low power microhotplate sensing technology are being established for target analytes in ambients that are relevant to process control, environmental measurements, and vapor-related remediation studies. We describe the use of these micromachined arrays to detect approximately ppm levels of methanol, benzene and hydrogen in ambient air and to produce analyte-specific signatures using temperature programs, T(t).
In this work, micromachining and planar processing have been used to produce gas sensing devices with lower power consumption at lower cost. The small size brings new advantages for chemical selectivity as well: multi-element arrays whose time-varying signals can be interpreted using pattern recognition methods. The device platform is a `microhotplate,' consisting of a built-in heater, thermometer, and electrodes to probe the sensing films. Microhotplates are fabricated using CMOS-compatible technologies, enabling on-chip circuitry for multiplexing and signal amplification.