Special Issue "Cantilever, Microcantilevers and Nanocantilever Sensors and Biosensors"
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A special issue of Sensors (ISSN 1424-8220). This special issue belongs to the section "Biosensors".
Deadline for manuscript submissions: closed (30 April 2008)
Special Issue Editor
Special Issue Information
Dear Colleagues,
In the last years, microcantilevers have been increasingly used as mechanical transducers of molecular recognition and for the development of miniaturized and sensitive biochip platforms. The principle is that intermolecular forces that result from molecular recognition events on the sensitised surface of a cantilever produce its nano-scale motion. Main techniques for the nanomechanical response include the optical lever method, interferometry-based methods, and the piezoresistivity technique. The optical lever method is the most extended due to the extreme accuracy and easy implementation for measuring cantilevers immersed in liquids. The applications include detection of cancer protein markers, pesticides, DNA hybridisation and pathogens. The great interest in these recent kind of biosensors relies on the label-free detection, high sensitivity, small sensor area, and the potential for simultaneous detection of tens, or even hundreds, of targets by making use of arrays of cantilevers. In fact, cantilever arrays can be mass-fabricated at low cost by adopting well-known semiconductor technology. Also, with microelectronics technology now pushing deep into the submicron regime, nanoelectromechanical systems (NEMS) are drawing interest from the scientific community for a wide range of applications due to their unique properties. Nanocantilevers are among those of the possible NEMS realizations that offer access to a parameter space that is unprecedented; fundamental resonant frequencies in the microwaves, active masses in the femtograms, heat capacities below a yoctocalorie, to name a few. Nanocantilever resonators have been proposed for ultrafast sensors and actuators, signal processing components and for quantum computing. Recent experiments have open up a new application, mass detection based on nanoresonators. The minuscule active mass of this elements allow to envision the detection of single molecules.
Topics
- Detection of gases and chemicals
- Biological detection
- Theoretical understanding of the nanomechanical response
- Fabrication of cantilever arrays for nanomechanical sensors
- Nanocantilevers
- Integration of nanomechanical sensors (microfluidics, actuators, sensors, CMOS)
- MEMS/NEMS technology for sensors
- SPM technology for molecular recognition imaging
- Transduction methods of the nanomechanical signal
Dr. Montserrat Calleja
Guest Editor
Submission
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Keywords
- microcantilever-based biosensors
- surface stress measurements
- mass detection
- microcantilevers
- nanocantilevers
- nano-micromechanical resonators
- nanomechanical sensors
- nanomechanics
- NEMS
- MEMS
- nanoresonators
Published Papers (12 papers)
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Received: 24 July 2007 / Accepted: 27 August 2007 / Published: 3 September 2007
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Abstract: A model for prediction the photostriction effect in silicon microcantilevers is built up based on the fundamentals of mechanics and semiconductor physics. By considering the spatial distribution and surface recombination of photoinduced carriers in silicon, the model interprets the cause of the photoinduced bending. The results from our model much more closely approximate the experimental values than the former model built up by Datskos, Rajic and Datskou [1](APL, Vol.73 (1998) No.16, pp 3219-2321), represented by the reduction of the error between calculation and measurement from 25 times to 0.85 times.
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Received: 30 July 2007 / Accepted: 4 September 2007 / Published: 5 September 2007
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Abstract: An analytical model for predicting the deflection and force of a bimaterialcantilever is presented. We introduce the clamping effect characterised by an axial loadupon temperature changes. This new approach predicts a non linear thermal dependence ofcantilever strain. A profilometry technique was used to measure the thermal strain.Comparison with experimental results is used to verify the model. The concordance of theanalytical model presented with experimental measurements is better than 10%
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Received: 27 July 2007 / Accepted: 6 September 2007 / Published: 7 September 2007
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Abstract: When microcantilevers are used in the dynamic mode, the resonance shift uponmaterial adsorption depends on the position of the adsorbate along the microcantilever. Wehave previously described that the adsorbate stiffness needs to be considered in addition toits mass in order to correctly interpret the resonance shift. Here we describe a method thatallows obtaining the Young’s modulus of the adsorbed bacteria derived from themeasurement of the frequency shift when adsorbates are placed close to the clampingregion. As a model system we have used E. Coli bacteria deposited on the cantileversurface by the ink-jet technique. We demonstrate that the correct information aboutadsorbed mass can be extracted by recording the cantilever profile and its resonanceresponse. Also, the position and extent of adsorbates is determined by recording themicrocantilever profile. We use a theoretical model based on the Euler – Bernouilliequation for a beam with both mass and flexural rigidity local increase due to the depositedmaterial.
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Received: 6 September 2007 / Accepted: 26 September 2007 / Published: 3 October 2007
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Abstract: Microfabrication limitations are of concern especially for suspended Micro-Electro-Mechanical-Systems (MEMS) microstructures such as cantilevers. The static anddynamic qualities of such microscale devices are directly related to the invariant and variantproperties of the microsystem. Among the invariant properties, microfabrication limitationscan be quantified only after the fabrication of the device through testing. However, MEMSare batch fabricated in large numbers where individual testing is neither possible nor costeffective. Hence, a suitable test algorithm needs to be developed where the test resultsobtained for a few devices can be applied to the whole fabrication batch, and also to thefoundry process in general. In this regard, this paper proposes a method to test MEMScantilevers under variant electro-thermal influences in order to quantify the effectiveboundary support condition obtained for a foundry process. A non-contact optical sensingapproach is employed for the dynamic testing. The Rayleigh-Ritz energy method usingboundary characteristic orthogonal polynomials is employed for the modeling andtheoretical analysis.
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Received: 27 August 2007 / Accepted: 10 October 2007 / Published: 17 October 2007
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Abstract: This paper presents a micro-scale air flow sensor based on a free-standingcantilever structure. In the fabrication process, MEMS techniques are used to deposit asilicon nitride layer on a silicon wafer. A platinum layer is deposited on the silicon nitridelayer to form a piezoresistor, and the resulting structure is then etched to create afreestanding micro-cantilever. When an air flow passes over the surface of the cantileverbeam, the beam deflects in the downward direction, resulting in a small variation in theresistance of the piezoelectric layer. The air flow velocity is determined by measuring thechange in resistance using an external LCR meter. The experimental results indicate that theflow sensor has a high sensitivity (0.0284 ω/ms-1), a high velocity measurement limit (45ms-1) and a rapid response time (0.53 s).
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Received: 18 October 2007 / Accepted: 21 November 2007 / Published: 22 November 2007
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Abstract: The magnetostrictive microcantilever (MSMC) as a high-performance transducer was introduced for the development of biosensors. The principle and characterization of MSMC are presented. The MSMC is wireless and can be easily actuated and sensed using magnetic field/signal. More importantly, the MSMC exhibits a high Q value and works well in liquid. The resonance behavior of MSMC is characterized in air at different pressures and in different liquids, respectively. It is found that the Q value of the MSMC in water reaches about 40. Although the density and viscosity of the surrounding media affect the resonance frequency and the Q value of MSMC, the density has a stronger influence on the resonance frequency and the viscosity has a stronger influence on the Q value, which result in that, for MSMC in air at pressure of less than 100 Pa, the resonance frequency of MSMC is almost independent of the pressure, while the Q value increases with decreasing pressure. MSMC array was developed and characterized. It is experimentally demonstrated that the characterization of an MSMC array is as simple as the characterization of a single MSMC. A filamentous phage against Salmonella typhimurium was utilized as bio-recognition unit to develop an MSMC based biosensor. The detection of S. typhimurium in water demonstrated that the MSMC works well in liquid.
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Received: 1 November 2007 / Accepted: 4 December 2007 / Published: 6 December 2007
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Abstract: A new concept using a near-field thermometry sensor is presented, employing atipless microcantilever experimentally validated for an aqueous medium within approximatelyone cantilever width from the solid interface. By correlating the thermal Brownian vibratingmotion of the microcantilever with the surrounding liquid temperature, the near-fieldmicroscale temperature distributions at the probing site are determined at separation distancesof z = 5, 10, 20, and 40 μm while the microheater temperature is maintained at 50°C, 70°C, or90°C. In addition, the near-field correction of the correlation is discussed to account for thequenched cantilever vibration frequencies, which are quenched due to the no-slip solid-wallinterference. Higher thermal sensitivity and spatial resolution is expected when the vibrationfrequencies increase with a relatively short and thick cantilever and the dimensions of themicrocantilever are reduced. Use of the microcantilever thermometry sensor can also reduce thecomplexity and mitigate the high cost associated with existing microfabricated thermocouplesor thermoresistive sensors.
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Received: 29 October 2007 / Accepted: 4 January 2008 / Published: 9 January 2008
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Abstract: The volume required for the rheological characterization of fluids can beminimized by using micromechanical cantilevers as viscosity sensors. Here, a simplemeasurement tool for the characterization of sugar solutions is proposed. The sensorconsists of a micromechanical cantilever as used in an atomic force microscopy which isintegrated into a closed fluid handling system. Fluid properties are derived from an analysisof the power spectral density of the fluctuations of the cantilever deflection signal. The dataacquisition system is operated with standard consumer computer components, which limitsthe costs for the hardware. Measurements with different sugar solutions indicate that thesensor system provides reliable viscosity values for sugar concentrations as they occur inbiological systems. The viscosities of the sugar solutions could be evaluated with an errorsmaller than 5 %.
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Received: 31 October 2007 / Accepted: 2 January 2008 / Published: 9 January 2008
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Abstract: Micromechanical devices such as microcantilevers (MC) respond to irradiationwith light by at least two different, photon-mediated processes, which induce MC bendingas a consequence of differential surface stress. The first and slow bending is due to theabsorption of photons, whose energy is transformed into heat and causes bending ofbimetallic microcantilevers due to thermal expansion. The second type of deflection is fastand caused by photons of sufficient energy to promote electrons across the Schottky barrierand thus create charge carriers, resulting in photoinduced stress that causes MC bending. Inthis study, the MC bending response to irradiation with light of wavelengths ranging from250 to 700 nm was investigated. Measurements of the immediate mechanical response tophotoinduced stress as a function of the wavelength of incident light provide an avenue tothe determination of the cut-off wavelength/energy of the Schottky barrier in the MCdevices under investigation. For a gold coated Si3Ni4 microcantilever we measured a cutoffwavelength of 1206 nm, which lies in the range of the literature value of 1100 nm.
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Received: 2 November 2007 / Accepted: 3 March 2008 / Published: 10 March 2008
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Abstract: Here, we present the activities within our research group over the last five yearswith cantilevers fabricated in the polymer SU-8. We believe that SU-8 is an interestingpolymer for fabrication of cantilevers for bio/chemical sensing due to its simple processingand low Young’s modulus. We show examples of different integrated read-out methodsand their characterisation. We also show that SU-8 cantilevers have a reduced sensitivity tochanges in the environmental temperature and pH of the buffer solution. Moreover, weshow that the SU-8 cantilever surface can be functionalised directly with receptormolecules for analyte detection, thereby avoiding gold-thiol chemistry.
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Received: 17 April 2008 / Accepted: 18 May 2008 / Published: 26 May 2008
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Abstract: Microcantilevers were first introduced as imaging probes in Atomic Force Microscopy (AFM) due to their extremely high sensitivity in measuring surface forces. The versatility of these probes, however, allows the sensing and measurement of a host of mechanical properties of various materials. Sensor parameters such as resonance frequency, quality factor, amplitude of vibration and bending due to a differential stress can all be simultaneously determined for a cantilever. When measuring the mechanical properties of materials, identifying and discerning the most influential parameters responsible for the observed changes in the cantilever response are important. We will, therefore, discuss the effects of various force fields such as those induced by mass loading, residual stress, internal friction of the material, and other changes in the mechanical properties of the microcantilevers. Methods to measure variations in temperature, pressure, or molecular adsorption of water molecules are also discussed. Often these effects occur simultaneously, increasing the number of parameters that need to be concurrently measured to ensure the reliability of the sensors. We therefore systematically investigate the geometric and environmental effects on cantilever measurements including the chemical nature of the underlying interactions. To address the geometric effects we have considered cantilevers with a rectangular or circular cross section. The chemical nature is addressed by using cantilevers fabricated with metals and/or dielectrics. Selective chemical etching, swelling or changes in Young’s modulus of the surface were investigated by means of polymeric and inorganic coatings. Finally to address the effect of the environment in which the cantilever operates, the Knudsen number was determined to characterize the molecule-cantilever collisions. Also bimaterial cantilevers with high thermal sensitivity were used to discern the effect of temperature variations. When appropriate, we use continuum mechanics, which is justified according to the ratio between the cantilever thickness and the grain size of the materials. We will also address other potential applications such as the ageing process of nuclear materials, building materials, and optical fibers, which can be investigated by monitoring their mechanical changes with time. In summary, by virtue of the dynamic response of a miniaturized cantilever shaped material, we present useful measurements of the associated elastic properties.
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Received: 4 March 2008; in revised form: 16 May 2008 / Accepted: 16 May 2008 / Published: 29 July 2008
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Abstract: We review the application of cantilever-based stress measurements in surface science and magnetism. The application of thin (thickness appr. 0.1 mm) single crystalline substrates as cantilevers has been used successfully to measure adsorbate-induced surface stress changes, lattice misfit induced film stress, and magneto-elastic stress of ferromagnetic monolayers. Surface stress changes as small as 0.01 N/m can be readily measured, and this translates into a sensitivity for adsorbate-coverage well below 0.01 of one layer. Stress as large as several GPa, beyond the elasticity limits of high strength materials, is measured, and it is ascribed to the lattice misfit between film and substrate. Our results point at the intimate relation between surface stress and surface reconstruction, stress-induced structural changes in epitaxially strained films, and strain-induced modifications of the magneto-elastic coupling in ferromagnetic monolayers.
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Last update: 8 March 2011
