Piezoelectric cantilever sensors

A piezoelectric cantilever with a non-piezoelectric, or piezoelectric tip useful as mass and viscosity sensors. The change in the cantilever mass can be accurately quantified by monitoring a resonance frequency shift of the cantilever. For bio-detection, antibodies or other specific receptors of target antigens may be immobilized on the cantilever surface, preferably on the non-piezoelectric tip. For chemical detection, high surface-area selective absorbent materials are coated on the cantilever tip. Binding of the target antigens or analytes to the cantilever surface increases the cantilever mass. Detection of target antigens or analytes is achieved by monitoring the cantilever's resonance frequency and determining the resonance frequency shift that is due to the mass of the adsorbed target antigens on the cantilever surface. The use of a piezoelectric unimorph cantilever allows both electrical actuation and electrical sensing. Incorporating a non-piezoelectric tip (14) enhances the sensitivity of the sensor. In addition, the piezoelectric cantilever can withstand damping in highly viscous liquids and can be used as a viscosity sensor in wide viscosity range

Flexural vibrations and resonance of piezoelectric cantilevers with a nonpiezoelectric extension

IEEE Transactions on Ultrasonics, Ferroelectrics and Frequency Control, 54(10): pp. 2001-2010.A piezoelectric cantilever (PEC) is a flexural transducer consisting of a piezoelectric layer [e.g., lead zirconate titanate (PZT)] bonded to a nonpiezoelectric layer (e.g., stainless steel). A PEC with a thin nonpiezoelectric extension has two distinctive sections, each with a different thickness, different axial density, and elastic-modulus profiles and has been increasingly used as an in-situ biosensor. It has the advantages of dipping only the nonpiezoelectric extension part in an aqueous solution without electrically insulating the piezoelectric section as well as serving as the bonding pad for receptor immobilization. In this study, we examined the effect of the thin nonpiezoelectric extension on the flexural resonance spectrum and resonance vibration waveforms of PEC; in particular, how the length ratio between the piezoelectric section and the nonpiezoelectric extension section affects the resonance frequencies and resonance peak intensities of PEC. Theoretical resonance frequencies and resonance vibration waveforms were obtained using an analytical transcendental equation we derived by solving the flexural wave equation. Both experimental and theoretical results showed that the two-section structure distorted the flexural vibration waveforms from those of PEC without an extension. As a result, the higher-mode resonance peaks of PEC with a nonpiezoelectric extension could be higher than the first resonance peak due to the two-section structure. With PEC that has a piezoelectric section of 0.25-mm thick PZT bonded to 0.07 mm thick stainless steel of various length l1 and a 0.07-mm thick nonpiezoelectric extension of length l2, we showed that the first-mode-to-second-mode resonance peak intensity ratio had a maximum of 5.6 at l1/l2 = 0.75 and the first-modeto- second-mode resonance frequency ratio a minimum of 2.2 at l1/l2 = 1.8. These findings will undoubtedly help optimize the design and performance of PEC

Probing elastic modulus and depth of bottom-supported inclusions in model tissues using piezoelectric cantilevers

Review of Scientific Instruments,78(11): pp. 115101-1-6.We have experimentally investigated the depth sensitivity limit of a piezoelectric cantilever tissue elastic modulus sensor and simultaneously determined the elastic modulus and the depth of a tumor directly. Using model tissues consisting of bottom-supported modeling clay inclusions of various depths in a gelatin matrix, we empirically determined that the depth sensitivity limit of a piezoelectric cantilever sensor was twice the linear dimension of the indentation area or the cantilever width . Knowing the depth sensitivity limit of the individual cantilever sensor as input and treating a model tissue that has the gelatin matrix on top and the modeling clay inclusion at the bottom as two springs in series, we showed that the elastic moduli and depths of the hard inclusions could be simultaneously determined with the elastic modulus profiles measured by two cantilevers with different widths as input

Non-heavy-metal ZnS quantum dots with bright blue photoluminescence by a one-step aqueous synthesis

Nanotechnology, 18(20): pp. 205604-1 - 205604-6.We have examined the aqueous synthesis of non-heavy-metal ZnS quantum dots (QDs) using 3-mercaptopropionic acid (MPA) as the capping molecule at various pH and MPA:Zn:S ratios. Transmission electron microscopy (TEM) and x-ray diffraction (XRD) indicated that the aqueous ZnS QDs were 3–5 nm in size with a zinc blende structure. We showed that, at pH 12 with a MPA:Zn:S = 8:4:1 ratio, the ZnS QDs with optimal blue emission could be obtained in a one-step, room-temperature aqueous process that exhibited a quantum yield of 31%, higher than that of the commercial CdSe/ZnS core–shell QDs. The present ZnS QDs could pass through a 50 kD filter. This indicated that they were smaller than 5 nm in size, consistent with those estimated from the UV–vis absorption edge and the TEM image. At a lower pH (e.g. pH = 8), the room-temperature synthesized ZnS QDs exhibited no photoluminescence. Although further hydrothermal annealing at 100 ◦C could improve the photoluminescence of the ZnS QDs, the resultant emission was not as bright as that obtained at pH 12 at room temperature. The blue emission of aqueous ZnS QDs was likely the result of trap-state emissions involving the defect states of the QDs. The present ZnS QDs were bright, small and contained non-heavy-metal elements, thus offering the potential for in vivo bioimaging

Self-exciting, self-sensing PbZr0.53Ti0.47O3 /SiO2 piezoelectric microcantilevers with femtogram/Hertz sensitivity

Applied Physics Letters, 89(2): pp. 3.Piezoelectric microcantilever sensors (PEMSs) consisting of a piezoelectric layer bonded to a nonpiezoelectric layer offer the advantages of electrical self-actuation and self-detection. Here we report PEMSs 60-300 mu m in length fabricated from 1.5-mu m-thick sol-gel PbZr0.53Ti0.47O3 (PZT). films with a 2 mu m grain size, a dielectric constant of 1600, and a saturation polarization of 55 +/- 5 mu C/cm(2). The PEMSs exhibited up to four resonance peaks with quality factors Q ranging from 120 to 320. In humidity sensing tests, a PEMS with a 60 x 25 mu m PZT/SiO2 section and a 24 x 20 mu m SiO2 extension exhibited 1 x 10(-15) g/Hz mass sensitivity, two orders of magnitude better than the sensitivity of the current PZT PEMS

All-electrical indentation shear modulus and elastic modulus measurement using a piezoelectric cantilever with a tip

Journal of Applied Physics, 101(5): pp. 054510-1 - 054510-10.We have investigated an all-electrical indentation shear modulus and elastic modulus measurement technique using piezoelectric cantilever sensors with a tip for potential in vivo applications. A piezoelectric cantilever with a tip was capable of carrying out compression, shear, indentation, and indentation shear tests, where compression and shear tests refer to those where the sample is not confined by a container and the contact area of the cantilever is the same as or larger than the sample surface area and the indentation and indentation shear tests are those where the contact area of the cantilever is smaller than the sample surface area. Because the cantilever could measure both the elastic modulus and the shear modulus, Poisson’s ratio of a sample could be determined from the ratio of the shear modulus to the elastic modulus with no presumption. We showed that the experimental elastic moduli and shear moduli obtained from the indentation and indentation shear tests agree with those obtained from the compression and shear tests. Furthermore, we showed that the same elastic moduli and the same shear moduli could be obtained either by using the displacement measurements or by the induced voltage measurements across the sensing piezoelectric layer. With a model tissue consisting of modeling clay embedded in gelatin, we demonstrated that the indentation compression and indentation shear tests could produce two-dimensional elastic and shear moduli maps or images that accurately showed the size and location of the modeling clay inclusion

Methyltrimethoxysilane-insulated piezoelectric microcantilevers for direct, all-electrical biodetection in buffered aqueous solutions

Review of Scientific Instruments, 77(12).We have examined coating PbMg1/3Nb2/3O3 0.63– PbTiO3 0.37 PMN-PT /tin piezoelectric microcantilever sensors PEMSs with a thin methyltrimethoxysilane MTMS by a simple solution method to electrically insulate the PEMS for biodetection in phosphate buffered saline PBS solutions. The PMN-PT/tin PEMSs were constructed using PMN-PT freestanding films that exhibited an electric-field-enhanced giant piezoelectric coefficient. The insulation procedure involved spin coatings of MTMS followed by cross-linking in water, which yielded a coating layer of about 10 nm in thickness on the tin side of the PEMS. We showed that the MTMS-insulated PMN-PT/tin PEMSs were capable of electrical self-excitation and self-sensing with a stable resonance spectrum exhibiting a quality factor of Q=50 when submerged in 0.1M PBS solution. Direct, all-electrical, in situ detection of Escherichia coli O157:H7 at various concentrations was demonstrated at a flow rate of 0.5 ml/min. A MTMS-insulated PMN-PT/tin PEMS 725 m long consisting of a 22- m-thick PMN-PT layer and a 6- m-thick tin layer exhibited a mass detection sensitivity m/ f =−3±2 10−12 g/Hz and a concentration sensitivity of better than 100 cells/ml in less than 1 ml of liquid

Modern Breast Cancer Detection: A Technological Review

Breast cancer is a serious threat worldwide and is the number two killer of women in the United States. The key to successful management is screening and early detection. What follows is a description of the state of the art in screening and detection for breast cancer as well as a discussion of new and emerging technologies. This paper aims to serve as a starting point for those who are not acquainted with this growing field