High-Quality Dry Etching of LiNbO3 Assisted by Proton Substitution through H2-Plasma Surface Treatment.

The exceptional material properties of Lithium Niobate (LiNbO3) make it an excellent material platform for a wide range of RF, MEMS, phononic and photonic applications; however, nano-micro scale device concepts require high fidelity processing of LN films. Here, we reported a highly optimized processing methodology that achieves a deep etch with nearly vertical and smooth sidewalls. We demonstrated that Ti/Al/Cr stack works perfectly as a hard mask material during long plasma dry etching, where periodically pausing the etching and chemical cleaning between cycles were leveraged to avoid thermal effects and byproduct redeposition. To improve mask quality on X- and Y-cut substrates, a H2-plasma treatment was implemented to relieve surface tension by modifying the top surface atoms. Structures with etch depths as deep as 3.4 µm were obtained in our process across a range of crystallographic orientations with a smooth sidewall and perfect verticality on several crystallographic facets.

A unifying model of weakly nonlinear elastic waves; large on large theory.

This article reconsiders traditional topics in nonlinear elastic waves and nonlinear ultrasonics. Herein, higher-order coupling between finite initial deformation and finite amplitude waves are considered. To allow for coupling, a large-on-large deformation model is developed and used to generate the equations of motion relative to the deformed and undeformed material configurations. Thus, the equations of motion provide a single setting to describe topics in nonlinear elastic waves such as acoustoelasticity, second harmonic generation, and coupling relations between these topics. The model is evaluated to recover the traditional linearized acoustoelastic relations and predicted second harmonic amplitudes. Then, the so-called large acoustoelasticity theory is developed for anisotropic materials with specific results given for isotropic materials. Last, the stress influence on second harmonic generation is presented.

Investigation of a Solid-State Tuning Behavior in Lithium Niobate.

Electric field-based frequency tuning of acoustic resonators at the material level may provide an enabling technology for building complex tunable filters. Tunable acoustic resonators were fabricated in thin plates (h/ λ  âˆ¼  0.05 ) of X-cut lithium niobate (LiNbO3) (90°, 90°, ψ = 170° ). LiNbO3 is known for its large electromechanical coupling ( K 2 ) for the shear and symmetric Lamb modes (SH0: K 2 = 40 %, S0: K 2 = 30 %) in thin plates and, thus, applicability for low-insertion loss and wideband filter applications. We demonstrate the effect of a dc bias in X-cut LiNbO3 to shift the resonant frequency by ~0.4% through direct tuning of the resonator material. A nonlinear acoustic computation predicted 0.36% tuning, which was in excellent agreement with the tuning measurement. For X-cut, we predicted electrical tuning of the S0 mode up to 1.6% and for Y-cut the electrical tuning of the SH0 and S0 modes was up to 7.0% with K 2 = 27.1 %. The mechanism is based on the nonlinearities that exist in the piezoelectric properties of LiNbO3. The X-cut SH0 mode resonators were centered near 335 MHz and achieved a frequency tuning of 6 kHz/V through the application of a dc bias.

Rapid Nucleic Acid Extraction and Purification Using a Miniature Ultrasonic Technique.

Miniature ultrasonic lysis for biological sample preparation is a promising technique for efficient and rapid extraction of nucleic acids and proteins from a wide variety of biological sources. Acoustic methods achieve rapid, unbiased, and efficacious disruption of cellular membranes while avoiding the use of harsh chemicals and enzymes, which interfere with detection assays. In this work, a miniature acoustic nucleic acid extraction system is presented. Using a miniature bulk acoustic wave (BAW) transducer array based on 36° Y-cut lithium niobate, acoustic waves were coupled into disposable laminate-based microfluidic cartridges. To verify the lysing effectiveness, the amount of liberated ATP and the cell viability were measured and compared to untreated samples. The relationship between input power, energy dose, flow-rate, and lysing efficiency were determined. DNA was purified on-chip using three approaches implemented in the cartridges: a silica-based sol-gel silica-bead filled microchannel, nucleic acid binding magnetic beads, and Nafion-coated electrodes. Using E. coli, the lysing dose defined as ATP released per joule was 2.2× greater, releasing 6.1× more ATP for the miniature BAW array compared to a bench-top acoustic lysis system. An electric field-based nucleic acid purification approach using Nafion films yielded an extraction efficiency of 69.2% in 10 min for 50 µL samples.

Rapid detection of Ebola virus with a reagent-free, point-of-care biosensor.

Surface acoustic wave (SAW) sensors can rapidly detect Ebola antigens at the point-of-care without the need for added reagents, sample processing, or specialized personnel. This preliminary study demonstrates SAW biosensor detection of the Ebola virus in a concentration-dependent manner. The detection limit with this methodology is below the average level of viremia detected on the first day of symptoms by PCR. We observe a log-linear sensor response for highly fragmented Ebola viral particles, with a detection limit corresponding to 1.9 × 104 PFU/mL prior to virus inactivation. We predict greatly improved sensitivity for intact, infectious Ebola virus. This point-of-care methodology has the potential to detect Ebola viremia prior to symptom onset, greatly enabling infection control and rapid treatment. This biosensor platform is powered by disposable AA batteries and can be rapidly adapted to detect other emerging diseases in austere conditions.

Elucidating the origin of spurious modes in aluminum nitride microresonators using a 2-D finite-element model.

In this work, an approach has been developed to predict the location of large spurious modes in the resonant response of aluminum nitride (AlN) microelectromechanical systems (MEMS) resonators over a wide range of desired operating frequencies. This addresses significant challenges in the design of more complex AlN devices, namely the prediction and elimination of spurious modes in the resonance response. Using the finite element method (FEM), the dispersion curves at wavelengths ranging from 8 to 20 µm were computed. It was determined that the velocities of symmetric Lamb (S0) and high-order antisymmetric (A) modes overlap at specific wavelengths. A 2-D FEM analysis showed that both the S0 and higher order A modes are mutually excited at a common operating wavelength. From this analysis, the coupling-of-modes (COM) parameters were extracted and used to compute the P-matrix and S-parameters using a 6-port transmission matrix. The P-matrix simulation was able to predict the electrical response of the S0 and nearby spurious modes. This work identified specific wavelength regions where COM has limited accuracy because of mode conversion. In these regions, the reflection (κ(p)) and transduction (ζ(p)) parameters change rapidly.

Rapid detection of human immunodeficiency virus types 1 and 2 by use of an improved piezoelectric biosensor.

Disasters can create situations in which blood donations can save lives. However, in emergency situations and when resources are depleted, on-site blood donations require the rapid and accurate detection of blood-borne pathogens, including human immunodeficiency virus types 1 and 2 (HIV-1 and HIV-2). Techniques such as PCR and antibody capture by an enzyme-linked immunosorbent assay (ELISA) for HIV-1 and HIV-2 are precise but time-consuming and require sophisticated equipment that is not compatible with emergency point-of-care requirements. We describe here a prototype biosensor based on piezoelectric materials functionalized with specific antibodies against HIV-1 and HIV-2. We show the rapid and accurate detection of HIV-1 and HIV-2 in both simple and complex solutions, including human serum, and in the presence of a cross-confounding virus. We report detection limits of 12 50% tissue culture infective doses (TCID50s) for HIV-1 and 87 TCID50s for HIV-2. The accuracy, precision of measurements, and operation of the prototype biosensor compared favorably to those for nucleic acid amplification. We conclude that the biosensor has significant promise as a successful point-of-care diagnostic device for use in emergency field applications requiring rapid and reliable testing for blood-borne pathogens.

Supramolecular self-assembling cyanine as an alternative to ethidium bromide displacement in DNA-drug model interactions during high throughput screening.

Supramolecular self-assembling cyanine and spermine binding to genomic DNA was a model for DNA-drug interactions during high throughput screening. Spermine competitively inhibited the self-assembly of cyanine upon DNA scaffolds as signaled by decreased fluorescence from the DNA-cyanine J-aggregate. The sequence of DNA exposure to cyanine or spermine was critical in determining the magnitude of inhibition. Methanol potentiated spermine inhibition by >10-fold. The IC(50) and association constant (K(a)) in 16% methanol were 0.35 +/- 0.03 microM and 2.86 x 10(6) M(-1) respectively, relative to 3.97 +/- 0.47 microM and 0.25 x 10(6) M(-1) respectively, in buffer. Increasing concentrations of cyanine overcame spermine inhibition, demonstrating the reversibility of DNA-drug interactions. LambdaDNA interacted similarly with spermine and cyanine, confirming system flexibility. The model drug, dye and methanol effects are discussed in detail. Cyanine might be a safer alternative to the mutagenic ethidium bromide for investigating DNA-drug interactions.

Spectroscopic analyses of the noncovalent self-assembly of cyanines upon various nucleic acid scaffolds.

We utilized self-assembly of cyanine chromophores to study the conformational changes in various types of nucleic acid scaffolds: single and double stranded DNA, linear or circular DNA and RNA. We identified a chromophore that became highly fluorescent after aggregating upon nucleic acids. Fluorescence from the aggregate was instantaneous after self-assembly. Temporal emission profiles displayed a biphasic trend demonstrating kinetic dependence for assembly and disassembly. Absorption spectra of the aggregate showed a red-shifted "shoulder" peak indicative of J-aggregate. Fluorescence from J-aggregates was also red-shifted. We utilized cyanine self-assembly to quantize various nucleic acids. The limits of detection and quantization for psiX174 DNA were 3 and 9 fmol, respectively. We similarly determined the sensitivity for various nucleic acids and established the optimum conditions for self-assembly. Collectively, the effects of methanol, salt, and full width at half maximum for cyanine fluorescence on DNA or carboxymethylamylose scaffolds, all suggested noncovalent, electrostatic, and hydrophobic forces were involved in supramolecular self-assembly. Our results facilitate a better understanding of supramolecular self-assembly.

Non-Faradaic electrochemical detection of protein interactions by integrated neuromorphic CMOS sensors.

Electronic detection of the binding event between biotinylated bovine serum albumen (BSA) and streptavidin is demonstrated with the chemoreceptive neuron MOS (CnuMOS) device. Differing from the ion-sensitive field-effect transistors (ISFET), CnuMOS, with the potential of the extended floating gate determined by both the sensing and control gates in a neuromorphic style, can provide protein detection without requiring analyte reference electrodes. In comparison with the microelectrode arrays, measurements are gathered through purely capacitive, non-Faradaic interactions across insulating interfaces. By using a (3-glycidoxypropyl)trimethoxysilane (3-GPS) self-assembled monolayer (SAM) as a simple covalent link for attaching proteins to a silicon dioxide sensing surface, a fully integrated, electrochemical detection platform is realized for protein interactions through monotone large-signal measurements or small-signal impedance spectroscopy. Calibration curves were created to coordinate the sensor response with ellipsometric measurements taken on witness samples. By monitoring the film thickness of streptavidin capture, a sensitivity of 25ng/cm2 or 2A of film thickness was demonstrated. With an improved noise floor the sensor can detect down to 2ng/(cm2mV) based on the calibration curve. AC measurements are shown to significantly reduce long-term sensor drift. Finally, a noise analysis of electrochemical data indicates 1/f(alpha) behavior with a noise floor beginning at approximately 1Hz.

Epoxy-silane linking of biomolecules is simple and effective for patterning neuronal cultures.

Surface chemistry is one of the main factors that contributes to the longevity and compliance of cell patterning. Two to three weeks are required for dissociated, embryonic rat neuronal cultures to mature to the point that they regularly produce spontaneous and evoked responses. Though proper surface chemistry can be achieved through the use of covalent protein attachment, often it is not maintainable for the time periods necessary to study neuronal growth. Here we report a new and effective covalent linking approach using (3-glycidoxypropyl) trimethoxysilane (3-GPS) for creating long term neuronal patterns. Micrometer scale patterns of cell adhesive proteins were formed using microstamping; hippocampal neurons, cultured up to 1 month, followed those patterns. Cells did not grow on unmodified 3-GPS surfaces, producing non-permissive regions for the long-term cell patterning. Patterned neuronal networks were formed on two different types of MEA (polyimide or silicon nitride insulation) and maintained for 3 weeks. Even though the 3-GPS layer increased the impedance of metal electrodes by a factor of 2-3, final impedance levels were low enough that low noise extracellular recordings were achievable. Spontaneous neural activity was recorded as early as 10 days in vitro. Neural recording and stimulation were readily achieved from these networks. Our results showed that 3-GPS could be used on surfaces to immobilize biomolecules for a variety of neural engineering applications.

Low-level detection of a bacillus anthracis simulant using Love-wave biosensors on 36 degrees YX LiTaO3.

We present an acoustic Love-wave biosensor for detection of the Bacillus anthracis simulant, Bacillus thuringiensis at or below inhalational infectious levels. The present work is an experimental study of 36 degrees YX cut LiTaO3 based Love-wave devices for detection of pathogenic spores in aqueous conditions. Given that the detection limit (D1) of Love-wave-based sensors is a strong function of the overlying waveguide, two waveguide materials have been investigated, which are polyimide and polystyrene. To determine the mass sensitivity of Love-wave sensor, bovine serum albumin (BSA) protein was injected into the Love-wave test cell while recording the magnitude and phase shift across each sensor. Polyimide had the lowest mass detection limit with an estimated value of 1.0-2.0 ng/cm2, as compared to polystyrene where D1 = 2.0 ng/cm2. Suitable chemistries were used to orient antibodies on the Love-wave sensor using protein G. The thickness of each biofilm was measured using ellipsometry from which the surface concentrations were calculated. The monoclonal antibody BD8 with a high degree of selectivity for anthrax spores was used to capture the non-pathogenic simulant B. thuringiensis B8 spores. Bacillus subtilis spores were used as a negative control to determine whether significant non-specific binding would occur. Spore aliquots were prepared using an optical counting method, which permitted removal of background particles for consistent sample preparation. This work demonstrates that Love-wave biosensors are promising for low-level detection for whole-cell biological pathogens.

Microcontact printing: a versatile technique for the study of synaptogenic molecules.

During synaptogenesis information exchanged locally between synaptic partners results in precise alignment of morphological and molecular specializations. For example, agrin derived from motoneurons induces localized postsynaptic differentiation at the neuromuscular synapse. Similar information molecules are thought to act at other synapses; however, techniques for directly evaluating synaptogenic activities of such molecules are lacking. Here we use agrin-induced differentiation as a model system to validate a novel approach for characterizing synaptogenic molecules. Proteins are patterned with micron scale resolution on glass coverslips by covalent microcontact printing and these substrates are used for cell culture. Postsynaptic molecules accumulate specifically at sites of contact between muscle cells and patterned agrin: a response which is quantifiable. Our results demonstrate that microcontact printing is applicable to the analysis of cellular response to locally immobilized information molecules.