Biomedical subjects

Mauricio Pereira da Cunha

Publications and source records attributed to Mauricio Pereira da Cunha.

8 recordsLinked to original sources

PubMed2006

Detection and identification of IHN and ISA viruses by isothermal DNA amplification in microcapillary tubes.

Unique base sequences derived from RNA of both infectious hematopoietic necrosis virus (IHNV) and infectious salmon anemia virus (ISAV) were detected and identified using a combination of surface-associated molecular padlock DNA probes (MPPs) and rolling circle amplification (RCA) in microcapillary tubes. DNA oligonucleotides with base sequences identical to RNA obtained from IHNV or ISAV were recognized by MPPs. Circularized MPPs were then captured on the inner surfaces of glass microcapillary tubes by immobilized DNA oligonucleotide primers. Extension of the immobilized primers by isothermal RCA produced DNA concatamers, which were labeled with fluorescent SYBR Green II nucleic acid stain, and measured by microfluorimetry. Molecular padlock probes, combined with this method of surface-associated isothermal RCA, exhibited high selectivity without the need for thermal cycling. This method is applicable to the design of low-power field sensors capable of multiplex detection of viral, bacterial, and protozoan pathogens within localized regions of microcapillary tubes.

Biosensing Techniques↗

PubMed2006

Nucleic acid sensing by regenerable surface-associated isothermal rolling circle amplification.

A novel method for regenerating biosensors has been developed in which the highly specific detection of nucleic acid sequences is carried out using molecular padlock probe (MPP) technology and surface-associated rolling circle amplification (RCA). This technique has a low occurrence of false positive results when compared to polymerase chain reaction, and is an isothermal reaction, which is advantageous in systems requiring low power consumption such as remote field sensing applications. Gold-sputtered 96-well polystyrene microplates and a fluorescent label were used to explore the detection limits of the surface-associated RCA technique, specificity for different MPP, conditions for regeneration of the biomolecular sensing surface, and reproducibility of measurements on regenerated surfaces. The technique was used to create highly selective biomolecular surfaces capable of discriminating between DNA oligonucleotides with sequences identical to RNA from infectious salmon anemia (ISA) and infectious hematopoietic necrosis (IHN) virus. As little as 0.6 fmol of circularized MPP was detectable with this fluorimetric assay. The sensing layers could be reused for at least four cycles of amplification using thermal denaturation, with less than 33% decrease in RCA response over time. Because the nucleic acid product of the test is attached to a surface during amplification, the technique is directly applicable to a variety of existing sensing platforms, including acoustic wave and optical devices.

Biosensing Techniques↗

PubMed2006

Pure SH-SAW propagation, transduction and measurements on KNbO3.

Potassium niobate (KNbO3) supports the electromechanically active pure shear horizontal surface acoustic wave (SH-SAW) mode along Z-axis cylinder orientations, Euler angles (phi, 90 degrees, 0 degrees), in which two uncoupled wave solutions exist: a purely mechanical sagittal Rayleigh SAW and a piezoelectrically stiffened pure SH-SAW. Within this family of cuts, a maximum electromechanical coupling coefficient for the pure SH-SAW, K2 = 53%, is observed along (0 degrees, 90 degrees, 0 degrees). This pure SH-SAW orientation also has the maximum value of electromechanical coupling observed along rotated Y-cut X propagation directions, Euler angles (0 degrees, theta, 0 degrees). The use of the pure SH-SAW mode is attractive for liquid-sensing applications because the SH-SAW is modestly attenuated by the adjacent liquid, unlike the generalized SAW (GSAW), which has particle displacement normal to the surface. This work investigates propagation and excitation properties of the SH-SAW and the shear horizontal bulk acoustic wave (SH-BAW) on single crystal KNbO3, Euler angles (0 degrees, 90 degrees, 0 degrees). Interdigital transducer (IDT) arrays are analyzed using boundary element method (BEM) techniques, addressing IDT properties such as: power partitioning between the SH-SAW and SH-BAW, SH-BAW radiation as a function of wave vector direction and radiation angle, and overall IDT impedance. The percentage of SH-SAW power to total input power is above 98% for IDTs containing 1.5 to 5.5 wavelengths of active electrodes with surrounding metalized regions. For nonmetalized regions outside the IDT, the ratio drops to between 1 and 2%, showing the importance of an energy trapping structure for efficient SH-SAW excitation and propagation along this orientation. Simulated and experimental IDT admittance results are compared, verifying the validity of the analysis performed. The reported measurements on the frequency variation with temperature indicate that the orientation considered is temperature compensated at about 8 degrees C. The surface of the SH-SAW devices fabricated have been loaded with deionized water and showed additional 1.6 dB transmission loss with respect to the unloaded surface, verifying the suitability of the pure SH-SAW mode on KNbO3 for liquid sensor applications.

Journal Article↗

PubMed2006

FEM/BEM impedance and power analysis for measured LGS SH-SAW devices.

Pure shear horizontal piezoelectrically active surface and bulk acoustic waves (SH-SAW and SH-BAW) exist along rotated Y-cuts, Euler angles (0 degrees, theta, 90 degrees), of trigonal class 32 group crystals, which include the LGX family of crystals (langasite, langatate, and langanite). In this paper both SH-SAW and SH-BAW generated by finite-length, interdigital transducers (IDTs) on langasite, Euler angles (0 degrees, 22 degrees, 90 degrees), are simulated using combined finite- and boundary-element methods (FEM/BEM). Aluminum and gold IDT electrodes ranging in thickness from 600 A to 2000 A have been simulated, fabricated, and tested, with both free and metalized surfaces outside the IDT regions considered. Around the device's operating frequency, the percent difference between the calculated IDT impedance magnitude using the FEM/BEM model and the measurements is better than 5% for the different metal layers and thicknesses considered. The proportioning of SH-SAW and SH-BAW power is analyzed as a function of the number of IDT electrodes; type of electrode metal; and relative thickness of the electrode film, h/wavelength, where wavelength is the SH-SAW wavelength. Simulation results show that moderate mechanical loading by gold electrodes increases the proportion of input power converted to SH-SAW. For example, with a split-electrode IDT, comprising 238 electrodes with a relative thickness h/wavelength = 0.63% and surrounded by an infinitesimally thin conducting film, nearly 9% more input power is radiated as SH-SAW when gold instead of aluminum electrodes are used.

Journal Article↗

PubMed2005

Platinum and palladium high-temperature transducers on langasite.

There is a pressing need for the fabrication of surface acoustic wave (SAW) devices capable of operating in harsh environments, at elevated temperature and pressure, or under high-power conditions. These SAW devices operate as frequency-control elements, signal-processing filters, and pressure, temperature, and gas sensors. Applications include gas and oil wells, high-power duplexers in communication systems, and automobile and aerospace combustion engines. Under these high-temperature and power-operating conditions, which can reach several hundred degrees Centigrade, the typically fabricated aluminum (A1) thin film interdigital transducer (IDT) fails due to electro and stress migration. This work reports on high temperature SAW transducers that have been designed, fabricated, and tested on langasite (LGS) piezoelectric substrates. Platinum (Pt) and palladium (Pd) (melting points at 1769 degrees C and 1554.9 degrees C, respectively) have been used as thin metallic films for the SAW IDTs fabricated. Zirconium (Zr) was originally used as an adhesion layer on the fabricated SAW transducers to avoid migration into the Pt or Pd metallic films. The piezoelectric LGS crystal, used as the substrate upon which the SAW devices were fabricated, does not exhibit any phase transition up to its melting point at 1470 degrees C. A radio frequency (RF) test and characterization system capable of withstanding 1000 degrees C has been designed and constructed. The LGS SAW devices with Pt and Pd electrodes and the test system have been exposed to temperatures in the range of 250 degrees C to 750 degrees C over periods up to 6 weeks, with the SAW devices showing a reduced degradation better than 7 dB in the magnitude of transmission coefficient, /S21/, with respect to room temperature. These results qualify the Pt and Pd LGS SAW IDTs fabricated for the above listed modern applications in harsh environments.

Journal Article↗

PubMed2004

A lateral field excited liquid acoustic wave sensor.

Lateral field excited (LFE) AT-cut quartz acoustic wave sensors in which the electrodes are located on the reference surface have been fabricated and tested in liquid environments. The sensing surface, which is opposite to the reference surface, is free allowing the electric field of the thickness shear mode (TSM) to penetrate into the liquid. This results in increased sensitivity to both mechanical and electrical property changes of the liquid. In the present paper, several 5-MHz LFE sensors with a range of electrode spacings were exposed to liquid environments in which the viscosity, relative permittivity, and conductivity were varied. The LFE sensors demonstrate sensitivity to viscosity that is more than twice that obtained for the standard quartz crystal microbalance (QCM), and sensitivity to relative permittivity and conductivity about 1.5 times that of the QCM sensors with modified electrodes. The present results clearly indicate that the LFE sensors may have a wide range of liquid phase applications in which sensitivity is crucial.

Journal Article↗

PubMed2004

Pure shear horizontal SAW biosensor on langasite.

The undetected introduction of pathogens into food or water supplies can produce grave consequences in terms of economic loss and human suffering. Sensitive and selective sensors capable of quickly detecting microbial pathogens are urgently needed to limit the effects of bioterrorist incidents, accidents, or pollution. Shear horizontal surface acoustic wave (SH SAW) devices provide an attractive platform for the design of microbial biosensors that function in liquid media, where Rayleigh-type modes are rapidly attenuated. This paper reports on an exploratory SH SAW delay line designed and fabricated on langasite, La3Ga5SiO14 (LGS), along the novel Euler propagation direction (0 degrees, 22 degrees, 90 degrees). A liquid chamber was fabricated and attached to the top surface, and the device was submitted to liquid and biochemical tests. Moderate (6 dB) additional attenuation of the transmission coefficient, /S21/, was consistently observed when the SH SAW delay line was assembled in the test fixture and submitted to the liquid tests, indicating that LGS is an attractive candidate for liquid sensing. Sensor selectivity can be achieved by integrating the LGS SH SAW delay line with a biochemical recognition layer. A test setup was implemented for the characterization of LGS SH SAW-based biosensors. The delay line response to biomolecule binding was shown by detection of sequential binding of proteins to the SH SAW device delay path. The biotinylated sensor was exposed sequentially to biotin-binding deglycosylated avidin, biotin-modified rabbit IgG, and goat anti-rabbit IgG antibody. As each protein was bound to the sensing surface, marked changes in the delay-line phase were recorded. The reported results demonstrate the capability of these devices to act as biochemical detectors in aqueous solutions, and this work represents the first effort using the novel material LGS in SAW-based biosensor technology.

Acoustics↗

PubMed2002

BAW temperature sensitivity and coupling in langanite.

One of the new materials belonging to the trigonal class 32, to which quartz belongs, is langanite (LGN, La3Ga5.5Nb0.5O14). High-quality LGN single crystals are now available, and, although similar in composition and structure to langasite (LGS, La3Ga5SiO14), LGN has smaller thermal expansion coefficients and comparable piezoelectric constants to LGS. These are desirable material properties for both SAW and BAW applications that require low frequency dependence on temperature. This paper examines in detail the LGN characteristics: phase velocity, temperature coefficient of frequency (TCF), electromechanical coupling coefficient, and power flow angle for both singly and doubly rotated plate cuts. Contour plots of these characteristics are constructed, revealing orientation regions where zero TCF and high coupling exist and suggesting potentially interesting cuts for practical BAW device design. Temperature compensated cut regions with coupling coefficients as high as 0.16 are predicted, which is twice the value for AT-cut quartz, along with a temperature compensated cut with cubic behavior around room temperature for one of the sets of material constants used. With such desirable properties, LGN is a promising candidate material for BAW applications requiring low temperature sensitivity with superior bandwidth characteristics due to its values of coupling coefficient larger than quartz. Several other orientations with low TCF and high coupling are also identified.

Acoustics↗