Introductory Fourier transform spectroscopy

Microcantilever arrays have been used for multiplexed, label-free detection of biomolecules. Adsorption of analyte molecules on immobilized receptors on the cantilevers result in cantilever bending due to surface free energy variation. Piezoresistive readout of cantilever bending offers a simple method of signal transduction that is compatible with microfabrication. Although the microcantilever-based biosensing appears to high sensitivity and selectivity, reproducibility of the technique appears to be a challenge. We have developed a novel method of immobilizing receptors that increases the reproducibility. We have demonstrated simultaneous detection of cancer and cardiac markers using cantilever arrays with immobilized receptors.

http://ieeexplore.ieee.org/iel5/4388307/4388308/04388320.pdf

Microcantilever Biosensors

This study presents the deflection, resonant frequency and stress results of rectangular, triangular, and step profile microcantilevers subject to surface stress. These cantilevers can be used as the sensing element in microcantilever biosensors. To increase the overall sensitivity of microcantilever biosensors, both the deflection and the resonant frequency of the cantilever should be increased. The effect of the cantilever profile change and the cantilever cross-section shape change is first investigated separately and then together. A finite element code ANSYS Multiphysics is used and solid finite elements cantilever models are solved. A surface stress of 0.05 N/m was applied to the top surface of the cantilevers. The cantilevers are made of silicon with elastic modulus 130 GPa and Poisson's ratio 0.28. To show the conformity of this study, the numerical results are compared against their analytical ones. Results show that triangular and step cantilevers have better deflection and frequency characteristics than rectangular ones.

https://www.mdpi.com/1424-8220/9/8/6046/pdf

Deflection, Frequency, and Stress Characteristics of Rectangular, Triangular, and Step Profile Microcantilevers for Biosensors

Arrays of microcantilevers are increasingly being used as physical, biological, and chemical sensors in various applications. To improve the sensitivity of microcantilever sensors, this study analyses and compares the deflection and vibration characteristics of rectangular and trapezoidal profile microcantilevers. Three models of each profile are investigated. The cantilevers are analyzed for maximum deflection, fundamental resonant frequency and maximum stress. The surface stress is modelled as in-plane tensile force applied on the top edge of the microcantilevers. A commercial finite element analysis software ANSYS is used to analyze the designs. Results show paddled trapezoidal profile microcantilevers have better sensitivity.

https://www.mdpi.com/1424-8220/9/4/2706/pdf

Comparison between Deflection and Vibration Characteristics of Rectangular and Trapezoidal profile Microcantilevers.

Detection of ultrasmall masses such as proteins and pathogens has been made possible as a result of advancements in nanotechnology. Development of label-free and highly sensitive biosensors has enabled the transduction of molecular recognition into detectable physical quantities. Microcantilever (MC)-based systems have played a widespread role in developing such biosensors. One of the most important drawbacks of all of the available biosensors is that they all come at a very high cost. Moreover, there are certain limitations in the measurement equipments attached to the biosensors which are mostly optical measurement systems. A unique self-sensing detection technique is proposed in this paper in order to address most of the limitations of the current measurement systems. A self-sensing bridge is used to excite piezoelectric MC-based sensor functioning in dynamic mode, which simultaneously measures the system's response through the self-induced voltage generated in the piezoelectric material. As a result, the need for bulky, expensive read-out equipment is eliminated. A comprehensive mathematical model is presented for the proposed self-sensing detection platform using distributed-parameters system modeling. An adaptation strategy is then implemented in the second part in order to compensate for the time-variation of piezoelectric properties which dynamically improves the behavior of the system. Finally, results are reported from an extensive experimental investigation carried out to prove the capability of the proposed platform. Experimental results verified the proposed mathematical modeling presented in the first part of the study with accuracy of 97.48%. Implementing the adaptation strategy increased the accuracy to 99.82%. These results proved the measurement capability of the proposed self-sensing strategy. It enables development of a cost-effective, sensitive and miniaturized mass sensing platform.

https://www.mdpi.com/1424-8220/13/5/6089/pdf

A Self-Sensing Piezoelectric MicroCantilever Biosensor for Detection of Ultrasmall Adsorbed Masses: Theory and Experiments

The problem of simultaneously enhancing sensitivity and noise immunity of microcantilevers is investigated. The dependence of deflection and resonant frequency of a microcantilever on its dimensions is studied. A principle to increase deflection and resonant frequency simultaneously is established. Several cantilevers agreeing with this principle are investigated using analytical models and are compared with FEM simulations. Using these results, a cantilever profile that achieves a larger deflection and a larger resonant frequency compared with uniform cantilevers is proposed to be used in sensor elements.

http://iopscience.iop.org/article/10.1088/0022-3727/40/24/009/pdf

Improved cantilever profiles for sensor elements

Microcantilevers are commonly used as part of sensor elements in Microelectromechanical Systems (MEMS). Deflection or the shift of resonance frequency of microcantilever beams are regularly used to measure chemical, physical or biological quantities. An important characteristic of any sensor is its sensitivity to a given input. This paper explores the possibility of improving the sensitivity of a microcantilever by modifying the mechanical properties using partial perforations on the surface of the microcantilever. This paper presents two analytical models that quantify the deflection and the fundamental resonant frequency in terms of the perforation dimensions for a microcantilever beam. Beams with a single partial perforation are considered first, and the models are then expanded to include multi-perforated cantilevers. Results obtained from the analytical models are compared to Finite Element Analysis (FEA) simulations of perforated microcantilever beams. The analytical models of a microcantilever with a single perforation show high accuracies compared to the FEA, while the accuracy of results for a cantilever beam with many perforations decrease as the number and size of perforations are increased. The results of the models are used to design a cantilever beam with the desired mechanical properties.

Maximising microcantilever response: an analytical approach using mathematical models

This paper presents a novel technique to extend the measurement range of interferometric microcantilever arrays far beyond the lambda/4 limit, while achieving a uniform resolution across the entire measurement range. It is shown that the diffraction pattern can be decomposed into a series of spatial harmonic functions, whose frequencies and phases are determined by the intercantilever distances and the cantilever deflections, respectively. Using this result, limitations of the standard interferometric methods are identified, and ways to overcome them are established. Using computer simulations, a microcantilever array that can measure deflections up to 5lambda unambiguously, with 0.2-nm resolution, is demonstrated. [2008-0285]

Extending the Deflection Measurement Range of Interferometric Microcantilever Arrays

This paper presents a novel technique to extend the measurement range of interferometric microcantilever arrays far beyond the λ/4 limit, while achieving a uniform resolution across the entire measurement range. It is shown that the diffraction pat- tern can be decomposed into a series of spatial harmonic functions, whose frequencies and phases are determined by the intercan- tilever distances and the cantilever deflections, respectively. Using this result, limitations of the standard interferometric methods are identified, and ways to overcome them are established. Using computer simulations, a microcantilever array that can measure deflections up to 5λ unambiguously, with 0.2-nm resolution, is demonstrated. (2008-0285)

Extending the Deflection Measurement Range of

Microcantilever sensors are commonly used as chemical and biological sensors. Interactions between the functionalisation layer on the cantilever and the analytes in the sample cause the cantilevers to bend. When the analyte concentration is low, these interactions are localized. Then, the same concentration can cause different deflections, depending upon the locations of interactions. The deflections will thus depend on the location of interaction, as well as the concentration of the analyte. This paper presents a model to calculate the deflection, when uni-axial surface stresses are distributed and localized. Results of this model are compared with finite element method simulation results. Biaxial stresses are then considered, and the one dimensional model is shown to be a valid approximation when the stresses are not applied at the ends. Using the model, characteristic response curves of a cantilever, when the surface stresses are localized, are obtained. The probability of determining a concentration based on an observed deflection is shown to be as low as 20%.

Sanchitha Fernando

Papers

Improved cantilever profiles for sensor elements

Maximising microcantilever response: an analytical approach using mathematical models

Extending the Deflection Measurement Range of Interferometric Microcantilever Arrays

Extending the Deflection Measurement Range of

Sensitivity analysis of cantilever biosensors