Deflection Sensitivity Research Articles

Regulation of cochlear hair cell function by intracellular calcium stores

IntroductionMammalian hearing depends on the dual mechanosensory and motor functions of cochlear hair cells. Both these functions may be regulated by Ca2+ release from intracellular stores. However, it is still unclear how exactly intracellular Ca2+ release may affect either hair cell mechano-electrical transduction (MET) or prestin-dependent electromotility in outer hair cells (OHCs).MethodsHere, we used photo-activatable (caged) compounds to generate fast increases of either Ca2+ or inositol-3-phosphate (IP3) in the cytosol of young postnatal rodent auditory hair cells, thereby stimulating either Ca2+- or IP3- induced releases of Ca2+ from intracellular stores. Fast Ca2+ imaging was used to monitor propagation of Ca2+ signals along the length of a hair cell. To access potential physiological role(s) of intracellular Ca2+ releases, we used whole cell patch clamp to record: i) OHC voltage-dependent capacitance, a known electrical correlate of prestin-based electromotility, and ii) MET currents evoked by stereocilia bundle deflections with fluid-jet. In the latter experiments, changes of mechanical stiffness of the hair bundles were also quantified from video recordings of stereocilia movements.ResultsCa2+ uncaging at the OHC apex initiated Ca2+ wave propagating to the base of the cell with subsequent Ca2+ build-up there. Ca2+ uncaging at the OHC base generated long-lasting and apparently self-sustained Ca2+ responses, further confirming Ca2+-induced Ca2+ release in the OHC basal region. Photoactivated IP3 initiated a slow increase of cytosolic Ca2+ ([Ca2+]i) throughout the whole OHC, confirming the presence of slow-activated IP3-gated Ca2+ stores in OHCs. Interestingly, Ca2+ uncaging produced no effects on OHC voltage-dependent capacitance. In an OHC, the rise of [Ca2+]i is known to decrease axial stiffness of the cell and may modulate the stiffness of mechanosensory stereocilia bundles. To separate these two phenomena, we explored the potential effects of intracellular Ca2+ release on mechanical properties of stereocilia bundles in cochlear inner hair cells (IHCs). Ca2+ uncaging at the apex of an IHC caused a long-lasting increase in mechanical stiffness of stereocilia bundle without any changes in the amplitude or deflection sensitivity of the MET current.DiscussionWe concluded that the most likely physiological role of IP3-gated Ca2+ release at the apex of the cell is the regulation of hair bundle stiffness. In contrast, Ca2+-induced Ca2+ release at the base of OHCs seems to regulate axial stiffness of the cells and its hyperpolarization in response to efferent stimuli, without direct effects on the OHC prestin-based membrane motors.

Application of active piezoresistive cantilevers in high-eigenmode surface imaging

Abstract One of the most important limitations of the atomic force microscopy (AFM) is scanning speed, whose high values are required for contemporary high-resolution, long-range diagnostic applications. The measurement bandwidth of an AFM depends on several factors, but usually results from the time constant of the oscillating cantilever, which is correlated with its resonance frequency and quality factor. We propose a method to overcome this problem by performing the surface measurements when the cantilever is vibrating in higher eigenmodes. In this paper we demonstrate the application of active piezoresistive cantilevers operating in this mode. The active piezoresistive cantilever comprises a piezoresistive deflection sensor, a deflection actuator and a nanotip. It is a complete micro-electro-mechanical system, ensuring the highest reliability of cantilever vibration control and detection. Higher eigenmode operations are usually difficult to implement as they usually result in lower deflection and lower sensitivity of the probe vibration deflection. Here we present an experimental modification of the structure of an active piezoresistive cantilever using focused ion beam machining that mitigates both weaknesses. This has enabled the cantilever to scan the surface at a scanning rate of 10 lines s−1 with a maximum speed of 500 μm s−1 and a data acquisition rate of 10 kS s−1, when the probe is vibrating at 380 kHz in the second eigenmode. We also describe a traceable calibration routine (based on analysis of the response of the piezoresistive detector, the output of the HeNe interferometer and precise control of the deflection actuator), together with the cantilever modification process and the development of the measurement setup. We show measurement results of dedicated calibration samples and silicon carbide crystal lattice references.

Folded flexure MOEMS for the detection of PSA and hepatitis DNA as biosensor for prostate cancer and viruses

Micro-opto-electro-mechanical systems (MOEMS) biosensors are employed in various applications such as disease monitoring, drug investigation, detection of pollutants, and biological fluid studies. In this paper, a novel MOEMS biosensor based on a differential folded-flexure structure is introduced. The designed device is employed to detect prostate-specific antigen (PSA) protein and Hepatitis DNA. The target molecules cause a mechanical deflection in the folded-flexure; subsequently, the transmitted optical power across the finger, attached to the flexure, is modulated in proportion to the input concentration. Then, a photodiode power sensor measures the modulated optical power, where the output of the sensor is simply a current related to the target molecules’ concentrations. The employed readout circuit operates at a wavelength of λ = 1550 nm with a laser power of 1 µW. The dimensions of the proposed biosensor are considered to be 365 × 340 × 2 μm³, making this sensor small enough and suitable for integration. The designed biosensor provides notable features of mechanical deflection sensitivities of 0.2053 nm/(ng/ml) and 7.2486 nm/nM, optical transmittance sensitivities of 0.535504 × 10−3 1/(ng/ml) and 18.91 × 10−3 1/nM, total output sensitivities of 0.5398 (mA/W)/(ng/ml) and 19.059 (mA/W)/nM, and measurement ranges of 0-1000 ng/ml and 0-28.33 nM for PSA and Hepatitis DNA, respectively. The proposed system is a sensitive and powerful sensor that can play an important role in diagnosing many diseases.

Optimizing the piezoresistive design on the microcantilever for enhancing stress sensing and temperature effects

This paper addresses the issue of volatile organic compounds (VOCs), hazardous materials commonly present in paints, perfumes, petroleum and oil refineries, and plastic products, which can lead to health hazards. The detection of these toxic compounds has been a compelling subject for researchers. In this study, a novel approach is presented, involving the design of a sensor for VOC determination using a piezoresistive microcantilever. Microcantilevers have gained significant attention in electrochemical applications due to their enhanced sensitivity. The research explores various design factors, such as length, thickness, and material selection, to optimize the sensor’s response. Specifically, reducing the cantilever’s thickness is considered to improve the deflection sensitivity. To enhance the sensitivity of the piezoresistive sensor, particular emphasis is placed on developing the piezoresistive sensing layer to effectively address stress-induced changes. Experimental investigations involve exploring different cantilever shapes and piezolayer configurations to achieve the desired optimized condition. Ultimately, the rectangular cantilever shape is reshaped into a U-shape, which demonstrates enhanced sensitivity, offering promising possibilities for VOC detection. This study presents valuable insights into the design and optimization of piezoresistive microcantilever sensors for efficient VOC detection, its temperature effects, and monitoring applications.

MEMS Sensor-Glasses Pair for Real-Time Monitoring of Intraocular Pressure

We present a novel implantable MEMS sensor – readout glasses pair towards the real-time monitoring of intraocular pressure. The overall system comprises i) a diffraction grating interferometric MEMS sensor to be embedded in the cornea and ii) readout glasses embedded with a laser diode, miniaturized aspheric lenses, and a CMOS camera. Owing to the abundance of diffracted orders, the proposed intraocular pressure measuring system offers ±8 degrees of eye tilt tolerance during monitoring via the camera. Furthermore, the use of one or multiple reference gratings adjacent to the sensor mitigates the effects of altering optical power (due to eye motion or laser noise) on the sensor. The design of the proposed device is justified with the analytical modeling of diffracted orders from the pressure sensor and ray-tracing simulations of the readout glasses. Through in-vitro measurements, we demonstrated a measurement range of ΔP = 40 mmHg pressure, with an average deflection sensitivity of 4.06 nm/mmHg and a resolution of 2.5 mmHg. With further development, the proposed system can be used for personalized real-time glaucoma monitoring.

An Ultrathin Internal Dielectric Actuator for Extended Range Deflection Pull-in Free Actuation

MEMS electrostatic actuators suffer from pull-in instability, making them highly nonlinear and limiting their useful range of motion. This report resolves the performance-limiting issues of the gap-closing transducer by using an ultrathin dielectric layer (UDL) for actuation. The device has an electromechanical coupling coefficient of 4.26% and an average deflection sensitivity of 119 nm/V over a range of 350 nm for upto 3.3 V dc bias. The UDL capacitance and deflection show a square law dependence on voltage. The device can thus be used as an actuator upto the full range of motion with better performance. Additionally, the UDL or gap capacitance can be used for feedback to maintain constant gap or strain. UDL actuation may also be combined with gap actuation to lower the pull-in voltage without changing the gap or the actuator thickness. 2022-0213

A monolithically integrated microcantilever biosensor based on partially depleted SOI CMOS technology

This paper presents a monolithically integrated aptasensor composed of a piezoresistive microcantilever array and an on-chip signal processing circuit. Twelve microcantilevers, each of them embedded with a piezoresistor, form three sensors in a Wheatstone bridge configuration. The on-chip signal processing circuit consists of a multiplexer, a chopper instrumentation amplifier, a low-pass filter, a sigma-delta analog-to-digital converter, and a serial peripheral interface. Both the microcantilever array and the on-chip signal processing circuit were fabricated on the single-crystalline silicon device layer of a silicon-on-insulator (SOI) wafer with partially depleted (PD) CMOS technology followed by three micromachining processes. The integrated microcantilever sensor makes full use of the high gauge factor of single-crystalline silicon to achieve low parasitic, latch-up, and leakage current in the PD-SOI CMOS. A measured deflection sensitivity of 0.98 × 10−6 nm−1 and an output voltage fluctuation of less than 1 μV were obtained for the integrated microcantilever. A maximum gain of 134.97 and an input offset current of only 0.623 nA were acquired for the on-chip signal processing circuit. By functionalizing the measurement microcantilevers with a biotin-avidin system method, human IgG, abrin, and staphylococcus enterotoxin B (SEB) were detected at a limit of detection (LOD) of 48 pg/mL. Moreover, multichannel detection of the three integrated microcantilever aptasensors was also verified by detecting SEB. All these experimental results indicate that the design and process of monolithically integrated microcantilevers can meet the requirements of high-sensitivity detection of biomolecules.

Formulation Analysis and Follow-Up Study of Differential MEMS Touch-Mode Sensor Utilizing Capacitive Vacuum Gauge Framework for Low-Pressure Measurements

Differential capacitance diaphragm gauges have become more popular in pressure measurements as they yield superior sensitivity and lesser non-linearity for pressure differential measurements. In addition, differential capacitance diaphragm gauges do not require a high vacuum reference cavity which reduces their manufacturing complexity. Efficient analysis for modelling differential capacitance diaphragm gauges is thus increasingly becoming vital due to their innumerable use cases. The higher sensitivity of circular diaphragm for the same side length in comparison to square diaphragm makes it ideal for sensor design. In this work, a complete formulation for analysis of differential capacitive vacuum gauge with the circular diaphragm in normal and touch mode operation has been presented for the low-pressure range of (1 to 1500 pascals). A comprehensive study of sensor parameters like capacitance, diaphragm deflection, capacitive and mechanical sensitivity has been formulated to aid the choice of sensor characteristics. Computationally complex methods have been used in the past for analysis of circular diaphragms. MATLAB and COMSOL have been used to compute and simulate results.

Determination of Staphylococcus Enterotoxin B Using a Flexible Aptamer-Based Biosensor

We demonstrate a fully flexible micromachined cantilever-based aptasensor for sensitive and specific sensing of Staphylococcus Enterotoxin B (SEB). The proposed flexible cantilever was fabricated using parylene-C as surface passivation layers and poly(3,4-ethylenedioxythiophene)/polystyrene sulfonate (PEDOT:PSS) as strain gauge for characterization of resistance. A spring constant of prepared cantilever was measured to be 12 nN/μm together with a deflection sensitivity of 1.42×10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-3</sup> /μm. With assembled 78-mer 5’-biotinylated aptamers on the sensing cantilever surface, the fully flexible aptasensor is capable of specific recognition SEB with a limit detection of 0.3 ng/mL. To evaluate the applicability of the proposed aptasensor, detections on raw milk spiked with SEB were implemented. The comparison indicates the prepared aptasensor could be qualified for SEB recognition in food contaminants detections, and the fully flexible cantilever-based sensors have tremendous potential for applications in food safety evaluation.

Drain current variation of extruded active area field-effect transistors on a silicon nitride membrane for low scale pressure of micro liter droplets

Extruded active area field-effect transistors (EA-FETs) with a silicon nitride membrane have been reported for low stress deflection sensing. EA-FETs have an extruded active area to improve the sensitivity of membrane deflection, whereas conventional metal-oxide-semiconductor field-effect transistors (MOSFETs) typically have a rectangle active area. EA-FETs are connected on edge of a silicon nitride membrane produced by potassium hydroxide wet etch of micro electromechanical systems (MEMS) while EA-FETs have a fundamental structure and operation property of MOSFETs. Proposed EA-FETs with a silicon nitride membrane showed 15.4% response of drain current variation by 1.5 μL deionized water droplets at 9 gate voltage while standard active area FETs showed 13.7% response under the same conditions. In addition, EA-FETs could measure isolated stress applied to the membrane without any other chemical reaction since the silicon nitride membrane of EA-FETs measured target materials separately.

Assessment and application of optical flow in background-oriented schlieren for compressible flows

Optical flow provides an opportunity to elevate the resolution and sensitivity of deflection sensing in background-oriented schlieren (BOS). Despite extensive relevant literature within the field of computer vision, there is a lack of proper quantification of its abilities and limitations with regard to the state-of-the-art BOS experiments. Thus, this study performs an assessment of accuracy and resolution limits in different flow field scenarios utilizing background patterns generated with random dot and wavelet noise distributions. Accordingly, a synthetic assessment over a theoretically generated Prandtl–Meyer expansion fan is conducted with variations introduced in the background patterns and operational parameters of optical flow. A clear superiority of accuracy and resolvable range of density gradient amplitudes over cross-correlation is demonstrated. Moreover, an experimental assessment of supersonic flow features over multiple wind tunnel models is performed. The influence of experimental constraints, limitations and uncertainties related to the application of optical flow in BOS and its comparative performance against the block-matching counterpart is characterized.Graphical abstract

Sensitivity Analysis of NEMS Cantilever to Detect Volatile Organic Compounds Using Finite Element Method

Nano Electro Mechanical System (NEMS) based cantilever is the alternate form of Micro Electro Mechanical system (MEMS) with dimensional changes in perspectives like thickness, length, and width. The advantage of the dimensional change leads to great improvement in sensitivity and performance with portable structure. In this paper, a stepped nanocantilever sensor is designed for the detection of volatile organic compounds. The same is compared with the conventional micro cantilevers in order to assess the sensitivity. The advantage of incorporating longitudinal cut at fixed end of the cantilever is investigated for different materials with load analysis and stress distributed results. COMSOL Simulation software is used to perform the analysis of nanocantilever and the result shows sensitivity increased with longitudinal cut and type of material which exhibits good sensitivity. In this research, we suggest a stepped cantilever structure that uses FEM (Finite Element Method) of analysis to calculate the change in deflection owing to various loads in both static and dynamic analyses. Similarly, changes in resonance frequency for changes in beam thickness are examined using parametric study. The experimental results from COMSOL simulation are found that the displacement occurred in proposed cantilever that the deflection sensitivity 2.85 x10-9m under maximum stress of 3.32 x10-9 N/m2. From the dynamic analysis, resonant frequency occurs at 20nm thickness is 2.8x107 Hz, and at 30nm is 3.5 x 107 Hz respectively.

Efficient in-depth analysis and optimum design parameter estimation of MEMS capacitive pressure sensor utilizing analytical approach for square diaphragm

Capacitive pressure sensors have become more popular as compared to piezoresistive pressure sensors as they yield superior sensitivity and lesser nonlinearity. Efficient analysis for modeling capacitive pressure sensors is thus increasingly becoming more important due to their innumerable use cases. The higher sensitivity of square diaphragm for the same side length in comparison to circular diaphragm makes it ideal for sensor design. In this work, a complete formulation for analysis of capacitive pressure sensor with the square diaphragm in normal and touch mode operation has been presented as these two modes are established operating modes for these sensors. A comprehensive study of sensor parameters like capacitance, diaphragm deflection, capacitive and mechanical sensitivity has been formulated to aid the choice of sensor characteristics. This work also focuses on the method to determine core design parameters for optimal operation. Computationally complex methods have been used in the past for analysis of square diaphragms. The analytical approach presented in this research is less complex and computationally efficient, in comparison to the finite element method. MATLAB has been used to compute and simulate results.

Forced vibration analysis of anisotropic curved panels via a quasi-3D model in orthogonal curvilinear coordinate

The present work involves a quasi-3D model in curvilinear coordinate to analyze time-dependent transversal deflection in aragonite curved nano-size panels. Eringen nonlocal deferential model has supported the small-scale phenomenon in nano-sized structures. To predict the effective elastic matrix ingredients in functionally graded aragonite panels, a function reported for anisotropic materials with an exponential variation in elastic properties through-thickness direction are utilized. Then, governing motion equations accounting for fourfold coupled (axial-shear-bending–stretching) components are gained on the basis of Hamilton statement and solved for simply-supported curved panel analytically. Ultimately, the sensitivity of transversal deflection and stresses to exponential factor, geometrical conditions, different curves, and nonlocality versus time are discussed in detail This work also supports a comparison between anisotropy and isotropic approximation to quantify the accuracy of replacing models to decrease the complexity; the differences in central deflection can grow up to 15%.

X-ray streak camera tube with two photocathodes

&lt;sec&gt;The time-resolved X-ray spectroscopy measurement system based on X-ray streak camera technology is indispensable diagnostic equipment in the study of laser inertial fusion research and high-energy-density physics. However, limited by the effective photocathode length of the X-ray streak tube, the time-resolved spectral measurement system usually used has the shortcomings of narrow spectrum range and poor spectral resolution.&lt;/sec&gt;&lt;sec&gt;In order to overcome the shortcomings, a novel dual-channel streak tube is developed, which consists of a photocathode, a prefocusing electrode group in temporal direction, an electric quadrupole lens electrode group, a main focusing electrode group in temporal direction, a deflector plate, and a phosphor screen. The photocathode has two slits. When X-rays are incident, two electron beams can be emitted simultaneously. The electric quadrupole lens electrode group is composed of 8 arc electrodes. Two electric quadrupole lenses are formed by the 8 arc electrodes in the spatial direction. Two electron beams emitted from the cathode of the streak tube are first accelerated and prefocused by the prefocusing electrode group in the time direction, and then compressed by the main focusing electrode group in the time direction. In the spatial direction, two electron beams are focused by the two electric quadrupole lenses independently. This novel streak tube structure can focus two electron beams at the same time, thereby increasing the effective photocathode length and maintaining the compact structure of streak tube without increasing the aberration.&lt;/sec&gt;&lt;sec&gt;The cathode voltage of the designed streak tube is –12 kV, the distance from cathode to grid is 5 mm, and the cathode-grid field strength is 2.4 kV/mm. The cathode is divided into two sections, the spacing between sections is about 13 mm, the length of each section is more than 20 mm, the magnification of the image converter tube is about 1.56 times, the distance between the cathode and the phosphor screen is 300 mm, and the longest size along the cathode direction is 90 mm. The test results of the performance of the streak tube show that the actual effective cathode length of the developed tube reaches 44 mm, the spatial resolution is better than 15 lp/mm, and the deflection sensitivity is better than 40 mm/kV. The effective cathode and spatial resolution of the tube can be increased to 50 mm and 25 lp/mm by further optimizing the structure of the tube and removing the image intensifier with a high sensitivity image recording system, respectively.&lt;/sec&gt;

Effects of nanometric plastic strain on the cantilever deflection sensitivity calibration accuracy for atomic force microscopy (AFM)-nanoindentation tests

Cantilever deflection sensitivity () calibration is a critical issue for a correct transduction of the electric signal into mechanical one in atomic force microscopy (AFM)-nanoindentation. Indenter-induced strains in calibration samples can negatively impact on the calibration reliability, becoming more important as the cantilever deflection () set for this calibration process is increased. In this work, we present a systematic study regarding the setpoint effects on the value calibration. setpoints between 0.05 and 1 [V] were considered for measurements, observing a clear decreasing trend in the value for 0.125 [V] concerning the most accurate value 192 [nm/V]. The results demonstrate that underestimations up to 10% concerning this value may be obtained by choosing non-adequate setpoints. This study shows the relevance of the setpoint for accurate calibration, which is essential for reliable quantitative studies of mechanical properties.

Structural damage identification based on dynamic deflection sensitivity of bridge under vehicle loading

Based on the concept of dynamic response sensitivity, a method of identifying bridge structural damage by using the dynamic deflection response of bridge under vehicle load is proposed. Firstly, the dynamic equation of vehicle-bridge coupling dynamic system is established. And then, the basic principle and iterative identification process of bridge damage identification based on dynamic deflection response sensitivity are derived. Finally, the effectiveness of the algorithm is verified with a numerical example of three-span continuous beam vehicle-bridge coupling system. The research results show that the proposed algorithm can overcome the influence of measurement noise and initial model error, and realize the damage location and quantification of bridge from dynamic deflections of a few measuring points.

A Flexible PI/Si/SiO2 Piezoresistive Microcantilever for Trace-Level Detection of Aflatoxin B1.

In this paper, a polyimide (PI)/Si/SiO2-based piezoresistive microcantilever biosensor was developed to achieve a trace level detection for aflatoxin B1. To take advantage of both the high piezoresistance coefficient of single-crystal silicon and the small spring constant of PI, the flexible piezoresistive microcantilever was designed using the buried oxide (BOX) layer of a silicon-on-insulator (SOI) wafer as a bottom passivation layer, the topmost single-crystal silicon layer as a piezoresistor layer, and a thin PI film as a top passivation layer. To obtain higher sensitivity and output voltage stability, four identical piezoresistors, two of which were located in the substrate and two integrated in the microcantilevers, were composed of a quarter-bridge configuration wheatstone bridge. The fabricated PI/Si/SiO2 microcantilever showed good mechanical properties with a spring constant of 21.31 nN/μm and a deflection sensitivity of 3.54 × 10−7 nm−1. The microcantilever biosensor also showed a stable voltage output in the Phosphate Buffered Saline (PBS) buffer with a fluctuation less than 1 μV @ 3 V. By functionalizing anti-aflatoxin B1 on the sensing piezoresistive microcantilever with a biotin avidin system (BAS), a linear aflatoxin B1 detection concentration resulting from 1 ng/mL to 100 ng/mL was obtained, and the toxic molecule detection also showed good specificity. The experimental results indicate that the PI/Si/SiO2 flexible piezoresistive microcantilever biosensor has excellent abilities in trace-level and specific detections of aflatoxin B1 and other biomolecules.

A synchroscan streak tube with high deflection sensitivity

A synchroscan streak tube with high spatiotemporal resolution and high deflection sensitivity is proposed, which contains several innovation designs. Some measures are taken to improve the imaging performances of the streak tube. Firstly, in order to obtain a high deflection sensitivity, the difference in voltage between the photocathode and anode and the length of the equipotential region of the streak tube are reduced as much as possible. Secondly, by introducing a hyperfine grid behind the cathode, reasonably designing the voltages applied to the six-electrode electrostatic focusing system, and moving the electron beam crossing point to the entrance of the deflection plates, the temporal dispersion and the temporal distortion of the streak tube are reduced, and the spatiotemporal resolution of the streak tube is improved. Besides, the streak tube is technically analyzed by tracking the temporal and spatial distribution of electrons under an operating voltage of 7000 V with the aid of computer simulation technology (CST) software. The results show that the deflection sensitivity is 125 mm/kV, the physical temporal resolution is better than 1.83 ps @MTF = 10%, and the static spatial resolution on the photocathode is better than 38 lp/mm @MTF = 10% over the effective photocathode area with a size of 10 mm × 4 mm. By applying a synchronous scanning voltage with a repetition frequency of 250 MHz to the deflection electrode, the results show that the dynamic spatial resolution of the streak tube is better than 16 lp/mm, the limit of the dynamic temporal resolution is 1.39 ps, and two rectangular electron pulses with a size of 10 mm × 20 μm and an interval of 2.3 ps emitted from the photocathode can be well resolved by the streak tube. In addition, the experimental measurements are conducted with a streak tube developed in our laboratory. The results demonstrate that the photocathode of the streak tube can work in the entire visible light region, and the response in the short wavelength region is significantly better than that in the long wavelength region. The static spatial resolution of this streak tube is 40 lp/mm in the center of the photocathode. The temporal resolution of this streak tube is 5.55 ps measured under a synchronous scanning voltage with a repetition frequency of 75 MHz.

A Low Spring Constant Piezoresistive Microcantilever for Biological Reagent Detection.

This paper introduces a piezoresistive microcantilever with a low spring constant. The microcantilever was fabricated with titanium (Ti) as the piezoresistor, a low spring constant polyimide (PI) layer, and a thin silicon oxide (SiO2) layer as the top and bottom passive layers, respectively. Excellent mechanical performances with the spring constant of 0.02128 N/m and the deflection sensitivity of 1.03 × 10−7 nm−1 were obtained. The output voltage fluctuation of a Wheatstone bridge, which consists of four piezoresistive microcantilevers, is less than 3 μV@3 V in a phosphate buffered saline (PBS) environment. A microcantilever aptasensor was then developed through functionalizing the microcantilevers with a ricin aptamer probe, and detections on ricin with concentrations of 10, 20, 50 and 100 ng/mL were successfully realized. A good specificity was also confirmed by using bovine serum albumin (BSA) as a blank control. The experiment results show that the Ti and PI-based microcantilever has great prospects for ultrasensitive biochemical molecule detections with high reliability and specificity.