Bulletin of the American Physical Society
2005 APS March Meeting
Monday–Friday, March 21–25, 2005; Los Angeles, CA
Session A4: Chemical and Biological Sensing with Microcantilevers |
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Sponsoring Units: GIMS Chair: A.T. Macrander, Argonne National Lab. Room: LACC 515A |
Monday, March 21, 2005 8:00AM - 8:36AM |
A4.00001: Cantilever Arrays as a platform for chemical and biological sensors Invited Speaker: Since the late 1980's there have been spectacular developments in micro-mechanical or micro-electro-mechanical (MEMS) systems which have enabled exploration of new transduction modes that involve mechanical energy and are based primarily on mechanical phenomena. As a result, an innovative family of chemical and biological sensors has emerged. While MEMS represents a diverse family of designs, devices with simple cantilever configurations are especially attractive as transducers for chemical and biological sensors. In our presentation we deal with four important aspects of cantilever transducers: (i) operation principles and models, (ii) micro-fabrication, (iii) figures of merit, and (iv) applications of cantilever sensors. We also provide a brief analysis of historical predecessors of the modern cantilever sensors. Finally we have demonstrated that using large well designed arrays of differentially coated microcantilevers coupled artificial neural network techniques can provide information on the identity and amount of target chemicals. We will present our results and discuss future directions. [Preview Abstract] |
Monday, March 21, 2005 8:36AM - 9:12AM |
A4.00002: Attogram detection using nanoelectromechanical oscillators Invited Speaker: We have used small mechanical oscillators as sensitive detectors of bound mass. Because the devices have very small mass, added mass of less than an attogram produces a readily observed shift in the resonant frequencies. For these experiments arrays of resonant devices of various geometries, made primarily from silicon-based materials, were fabricated by electron beam lithography, photolithography or other techniques. We used optical interference techniques to transduce the structure motion as this provides a simple non-contact method for interrogating arrays of oscillators. Chemically selective coatings were used to make the devices respond to specific chemicals, biomolecules, viruses or bacteria. Localizing the specific binding compounds to a nanoscale dot on the oscillator creates a device with a calibrated response to the binding of a few discrete particles from a small volume sample. In this talk we will describe the design, fabrication, mechanical response and use of these devise as specific mass detectors. [Preview Abstract] |
Monday, March 21, 2005 9:12AM - 9:48AM |
A4.00003: Multifunctional self-sensing microcantilever arrays for detection of chemicals and explosives Invited Speaker: Micromachined cantilevers lend themselves well to numerous sensing applications wherein the presence of an analyte is manifested mechanically in cantilever deflection and/or a resonance frequency change. The sensitivity, compactness, cost, power-consumption, scalability, and versatility of microcantilever sensors will continue to drive their appeal in numerous applications. Most cantilever systems to date have been relegated to lab use because they are cumbersome and bulky, requiring extensive setup efforts, alignment and calibration. Commercially available cantilevers require external sensing with optical systems and external actuation. Piezoelectric sensing elements eliminate the need for external optics and external actuators; piezoelectric cantilevers have low power consumption in the sensing element due to their high impedance and low drive- voltage requirements. They have the inherent strength of self-sensing and integrated actuation, meaning that the actuation signal can also be monitored as a sensor signal, and each element can be actuated independently and directly. The self sensing method enables compact and scalable cantilever sensing applications that were previously unfeasible. We have recently demonstrated a novel piezoelectric microcantilever array platform, with and without selective coatings, for detection of various chemicals and explosives. We have also demonstrated the ability to heat the cantilever, and measure both heat and impedance changes in addition to mass loading and unloading. This multidimensional approach offers a unique advantage for chemical selectivity and will be compared with other cantilever and non-cantilever methods. [Preview Abstract] |
Monday, March 21, 2005 9:48AM - 10:24AM |
A4.00004: Diamond-based MEMS devices for biosensing based on electrochemical and gravimetric Invited Speaker: Diamond offers several potential advantages as a platform material for bioinorganic interfaces, including chemical and bio-inertness, electrochemistry, and high acoustic velocity. Ultrananocrystalline diamond (UNCD), with a unique combination of physical, chemical and electrical properties, is attractive for a variety of biochemical/biomedical applications such as hermetic bio-inert coatings, MEMS compatible biosensors, and electrochemical biointerfaces. Over the past several years we have worked on both the fundamental and applied science related to enabling UNCD-based bioMEMS devices, which has encompassed both the development of UNCD surface functionalization strategies that allow fine control of surface hydrophobicity and bioactivity, as well as the development of material integration strategies and surface micromachining techniques to enable the microfabrication of UNCD structural layers (e.g. cantilevers) that incorporate these functionalized surfaces into MEMS devices which are back-end compatible with CMOS electronics. These devices could thus combine the electrochemical and gravimetric transduction of the selective adsorption of target analytes in MEMS structures fabricated directly on top of a silicon microchip.. In the past year we have successfully demonstrated the use of conducting UNCD thin films as electrochemical biointerfaces, via the successful attachment of a redox enzyme onto the UNCD surface, Glucose oxidase (GOD). The procedure to achieve GOD immobilization involved the electrochemical immobilization of nitrophenyl groups to the UNCD surface and transformation of nitrophenyl to aminophenyl groups and the covalent bonding of GOD to the carboxyl groups using the diisopropylcarbodiimide/ N-hydroxysuccinimide (DCC/NHS) as the catalyst. After immobilization, the activity of the enzyme was demonstrated via the direct electrochemical detection of hydrogen peroxide. We have also developed CMOS-compatible UNCD MEMS cantilevers and fixed-fixed beam structures, using both traditional photolithography and e-beam lithography techniques. [Preview Abstract] |
Monday, March 21, 2005 10:24AM - 11:00AM |
A4.00005: Nano-mechanical Resonantor Sensors for Virus Detection Invited Speaker: Micro and nanoscale cantilever beams can be used as highly sensitive mass detectors. Scaling down the area of the cantilever allows a decrease in minimum detectable mass limit while scaling down the thickness allows the resonant frequencies to be within measurable range. We have fabricated arrays of silicon cantilever beams as nanomechanical resonant sensors to detect the mass of individual virus particles. The dimensions of the fabricated cantilever beams were in the range of 4-5 $\mu $m in length, 1-2 $\mu $m in width and 20-30 nm in thickness. The virus particles we used in the study were vaccinia virus, which is a member of the Poxviridae family and forms the basis of the smallpox vaccine. The frequency spectra of the cantilever beams, due to thermal and ambient noise, were measured using a laser Doppler vibrometer under ambient conditions. The change in resonant frequency as a function of the virus particle mass binding on the cantilever beam surface forms the basis of the detection scheme. We have demonstrated the detection of a single vaccinia virus particle with an average mass of 9.5 fg. Specific capture of the antigens requires attachment of antibodies, which can be in the same range of thickness as these cantilever sensors, and can alter their mechanical properties. We have attached protein layers on both sides of 30nm thick cantilever beams and we show that the resonant frequencies can increase or decrease upon the attachment of protein layers to the cantilevers. In certain cases, the increase in spring constant out-weighs the increase in mass and the resonant frequencies can increase upon the attachment of the protein layers. These devices can be very useful as components of biosensors for the detection of air-borne virus particles. [Preview Abstract] |
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