Interfacial nucleic acid chemistry studied by acoustic shear wave propagation

Acoustic wave devices have continued to gain attention as biosensor structures because of their relative ease of operation and sensitivity to interfacial biochemical events. In the present paper, we review the use of the thickness-shear mode device for the label-free detection of processes involving nucleic acid moieties that are imposed at the sensor-liquid interface. Following a concise discussion of the theory and technology connected to the operation of the sensor in liquids, we outline a number of protocols that have been adopted for the attachment of oligonucleotides to sensor surfaces, many of which have been employed in ultrasonic biosensing. The various categories of applications are then surveyed in some detail. By far, the largest group is the study of duplex formation at the sensor surface, involving a compendium of experiments involving complementary and mismatched sequences. Considerably less attention has been paid to the detection of interaction of surface-bound nucleic acids with small molecules such as specific-binding peptides and drugs.A comprehensive appraisal of the literature in this field strongly suggests that acoustic coupling phenomena are particularly sensitive to interfacial physical chemistry. Accordingly, acoustic shear wave technology offers unique advantages over other sensor configurations because of its ability to produce multidimensional information through the recording of various parameters obtained from acoustic network analysis.     

Microparticle collection and concentration via a miniature surface acoustic wave device

The ability to detect microbes, pollens and other microparticles is a critically important ability given the increasing risk of bioterrorism and emergence of antibiotic-resistant bacteria. The efficient collection of microparticles via a liquid water droplet moved by a surface acoustic wave (SAW) device is demonstrated in this study. A fluidic track patterned on the SAW device directs the water droplet's motion, and fluid streaming induced inside the droplet as it moves along is a key advantage over other particle collection approaches, because it enhances microparticle collection and concentration. Test particles consisted of 2, 10, 12 and 45 microm diameter monodisperse polystyrene and melamine microparticles; pollen from the Populus deltoides, Kochia scoparia, Secale cerale, and Broussonetia papyrifera (Paper Mulberry) species; and Escherichia coli bacteria. The collection efficiency for the synthetic particles ranged from 16 to 55%, depending on the particle size and surface tension of the collection fluid. The method was more effective in collecting pollen and the bacteria with an efficiency of 45-68% and 61.0-69.8%, respectively. Pollen collection was strongly influenced by its diameter, size, and surface geometry in a manner contrary to initial expectations. Reasons for the consistent yet unexpected collection results include leaky SAW pressure boundary segregation and shear-induced concentration of larger particles, and the subtle effects of wetting interactions. These results demonstrate a new method for collecting microparticles requiring only about one second per run, and illustrate the inadequacy of using synthetic microparticles as a substitute for their biological counterparts in experiments studying particle collection and behavior.     

Planar chip device for PCR and hybridization with surface acoustic wave pump

We have developed a microfluidic device operating at a planar surface instead of a closed channel network. The fluid is transported in single droplets using surface acoustic waves (SAW) on a piezoelectric LiNbO(3) substrate. The surface of the piezo is chemically structured to induce high contact angles of the droplets or enclose areas where the liquid can wet the substrate. Combining the SAW technique with thin film resistance heaters, a biological analysis chip with integrated DNA amplification by PCR and hybridization was designed. To prevent evaporation of the PCR reagents at high temperatures the sample is enclosed in droplets of mineral oil. On this chip the SAW resolves dried primers, shifts the oil capped liquid between the two heaters and mixes during hybridization. The chip is able to perform a highly sensitive, fast and specific PCR with a volume as low as 200 nl. During the temperature cycles an online monitoring of the DNA concentration is feasible with an optical unit, providing a sensitivity of 0.1 ng. After PCR the product is moved to the second heater for the hybridization on a spotted DNA array. With our chip we were able to detect a single nucleotide polymorphism (SNP) responsible for the Leiden Factor V syndrome from human blood.     

Non-equilibrium shear relaxation in liquids

A theory for non-equilibrium shear relaxation in liquids at low frequencies is presented. It is based on molecular considerations used in theories of low frequency depolarized light scattering.The results for the complex shear impedance contain terms in addition to those obtained by the phenomenological relaxation theory.     

Mechanism of operation and design considerations for surface acoustic wave device vapour sensors

Surface acoustic wave (SAW) devices offer many attractive features for application as vapour phase chemical microsensors. This paper describes the characteristics of SAW devices and techniques by which they can be employed as vapour sensors. The perturbation of SAW velocity by polymeric coating films is investigated both theoretically and experimentally. Highest sensitivity can be achieved when the device is used as the resonating element in a delay line oscillator circuit. A simple equation has been developed from theoretical considerations which offers reasonably accurate quantitative predictions of SAW device frequency shifts when subjected to a given mass loading. In this mode the SAW device behaves very like conventional bulk-wave quartz crystal microbalances except that the sensitivity can be several orders of magnitude higher and the device size can be several orders of magnitude smaller. Detection of mass changes of a few femtograms by a SAW device having a surface area of 10⁻⁴ cm² is theoretically possible.     

Ionic liquids in the synthesis and modification of polymers

Ionic liquids are organic salts that are liquid at ambient temperatures, preferably at room temperature. They are nonvolatile, thermally and chemically stable, highly polar liquids that dissolve many organic, inorganic, and metallo‐organic compounds. Many combinations of organic cations with different counterions are already known, and the properties of ionic liquids may be adjusted by the proper selection of the cation and counterion. In the last decade, there has been increasing interest in using ionic liquids as solvents for chemical reactions. The interest is stimulated not only by their nonvolatility (green solvents) but also by their special properties, which often affect the course of a reaction. In recent years, ionic liquids have also attracted the attention of polymer chemists. Although the research on using ionic liquids in polymer systems is still in its infancy, several interesting possibilities have already emerged. Ionic liquids are used as solvents for polymerization processes, and in several systems they indeed show some advantages. In radical polymerization, the k_p/k_t ratio (where k_p is the rate constant of propagation and k_t is the rate constant of termination) is higher than in organic media, and thus better control of the process can be achieved. Ionic liquids, as electrolytes, have also attracted the attention of researchers in the fields of electrochemical polymerization and the synthesis of conducting polymers. Finally, the blending of ionic liquids with polymers may lead to the development of new materials (ionic liquids may act as plasticizers, electrolytes dispersed in polymer matrices, or even porogens). In this article, the new developments in these fields are briefly discussed. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 4675–4683, 2005     

Bulk and shear relaxation in glasses and highly viscous liquids

The ratio δB/δG between the couplings of a relaxational process to compression and shear, respectively, is calculated in the Eshelby picture of structural rearrangements within a surrounding elastic matrix, assuming a constant density of stable structures in distortion space. The result is compared to experimental data for the low-temperature tunneling states in glasses and to Prigogine-Defay data at the glass transition, both from the literature.     

A thin liquid film thickness shear mode bulk acoustic wave sensor for determination of Proteus mirabilis

A thickness shear mode bulk acoustic wave sensor coated with a thin liquid culture medium film was developed and applied to determine the concentration of Proteus mirabilis (P. mirabilis). Experiments demonstrated that there was a good linear relationship between the turning point time and the logarithm of the P. mirabilis concentration in the range 2.0 x 10(2)-2.0 x 10(6) cells ml(-1). The detection was fast and accurate because of the sharp turning point of the response due to the thin culture film on the sensor surface. Other problems concerning the experiments are discussed in detail.     

On the superposition of oscillatory and shear flows of viscoelastic liquids

Important flow enhancement effects take place when the motion of a non-Newtonian fluid is driven either by pressure gradients pulsating around a non-zero mean or by longitudinal and transversal boundary waves superposed on Poiseuille flow. Flow enhancement in the latter case is an order of magnitude larger than in the former. A regular perturbation in terms of the amplitude of the oscillation is used and closed form formulas given for mass transport rates at the lowest significant order. In particular it is shown that a mean flow may be generated even when the pressure gradients oscillate around a zero mean or the boundary waves are superposed on a fluid at rest if the frequencies of two superposed waves are in certain ratios.     

Mechanism of the modification of polyolefins by organosilicon liquids

Conclusions Thermochemical modification of polyolefins with organosilicon liquids of linear structure leads to the formation of the copolymers of the following structure: Si-O-R and Si-0-CH₂-R, where R is the polyolefin radical.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 4, pp. 797–801, April, 1970.     

The origin of persistent shear stress in supercooled liquids

The persistence of shear stress fluctuations in viscous liquids is a direct consequence of the non-zero shear stress of the local potential minima which couples stress relaxation to transitions between inherent structures. In simulations of 2D and 3D glass forming mixtures, we calculate the distribution of this inherent shear stress and demonstrate that the variance is independent of temperature and obeys a power law in density. The inherent stress is shown to involve only long wavelength fluctuations, evidence of the central role of the static boundary conditions in determining the residual stress left after the minimization of the potential energy. A temperature T(η) is defined to characterise the crossover from stress relaxation governed by binary collisions at high temperatures to low temperature relaxation dominated by the relaxation of the inherent stress. T(η) is found to coincide with the breakdown of the Stokes-Einstein scaling of diffusion and viscosity.     

The complex shear modulus of polymeric and small-molecule liquids

The complex shear moduli of some ordinary liquids and their dependence on the shear deformation angle have been measured by the resonance method at a frequency of 73.5 kHz. From the results obtained, it is concluded that liquids exhibit a low-frequency shear elasticity—a property unknown before—which is associated with collective interactions of liquid molecules.     

High‐sensitive neural network ammonia sensor based on shear horizontal surface acoustic wave devices

In this paper, a shear horizontal surface acoustic wave devices coated with L‐glutamic acid hydrochloride were applied as ammonia sensors. This sensor has shown high sensitivity and fast responses to ppb‐level ammonia. The frequency shift linearly increased as the ammonia concentration increased from 40 to 400 ppb in dry environment. In the humid environment, the frequency shift gradually decreased with ammonia concentration increasing. In order to precisely estimate the ammonia in humid environment, two different neural models, the conventional feedforward neural network and quantum neural network, were used as the identifier and their performances were reported and compared. Copyright © 2008 John Wiley & Sons, Ltd.     

Surface acoustic wave nebulization device with dual interdigitated transducers improves SAWN‐MS performance

We compared mass spectrometric (MS) performance of surface acoustic wave nebulization (SAWN) generated by a single interdigitated transducer (IDT) designed to produce a progressive wave (PW) to one with a dual IDT that can in theory generate standing waves (SW). Given that devices using dual IDTs had been shown to produce fewer large size droplets on average, we hypothesized they would improve MS performance by improving the efficiency of desolvation. Indeed, the SW‐SAWN chip provided an improved limit of detection of 1 femtomole of peptide placed on chip making it 100× more sensitive than the PW design. However, as measured by high‐speed image recording and phase Doppler particle analyzer measurements, there was only a 26% increase in the small diameter (1–10 µm) droplets produced from the new device, precluding a conclusion that the decrease in droplet size was solely responsible for the improvement in MS signal/noise. Given that the dual IDT design produced a more instantaneous plume than the PW design, the more likely contributor to improved MS signal/noise was concluded to be a higher ion flux entering the mass spectrometer for the dual IDT designs. Notably, the dual IDT device allowed production of much higher quality protein mass spectra up to about 20 kDa, compared with the single IDT device. Copyright © 2016 John Wiley & Sons, Ltd.     

The detection of organosphosphonates by polymer films on a surface acoustic wave device and a micromirror fiberoptic sensor

There is a need for sensitive detection of organophosphonates by inexpensive, portable instruments. Two kinds of chemical sensors, based on surface acoustic wave (SAW) devices and fiberoptic micromirrors, show promise for such sensing systems. Chemically sensitive coatings are required for detection, and data for thin films of the polymer polysiloxane are reported for both kinds of physical transducers. Both kinds of sensors are shown to be capable of detecting concentrations of diisopropylmethylphosphonate (DIMP) down to 1 ppm.     

Interaction of cytolytic toxin CytB with a supported lipid bilayer: study using an acoustic wave device

An acoustic technique was used to monitor the interaction of the pore-forming cytolytic toxin CytB with a positively charged supported lipid bilayer. The acoustic device, which is based on a waveguide geometry, is sensitive to changes in the mass of the supported bilayer. The specificity of the interaction, rate and extent of the association, reversibility and effect of previous depositions of toxin were investigated. The CytB was found to bind irreversibly to the lipids at all fractional coverages even when the protein-to-lipid ratio was high enough to imply that the protein was associating with the external surface of the bilayer. The CytB formed stable structures with the bilayer at high protein surface concentrations and did not appear to disrupt the bilayer in the manner of a detergent. The rate of association with the bilayer was found to be directly proportional to the solution concentration of CytB at higher concentrations but appeared to be low at a CytB solution concentration of 5 microg mL(-1), leading to relatively low amounts of CytB being associated with the bilayer.     

New ionic liquids for modification of chitin particles

Research on Chemical Intermediates - Chitin particles are chemically and mechanically stable due to the strong inter- and intra-sheet network of hydrogen bonds and the large number of crystalline...     

Measurements of the complete solvation response in ionic liquids

Dynamic Stokes shift measurements of the solvatochromic probe trans-4-dimethylamino-4'-cyanostilbene were used to measure the solvation response of five imidazolium and one pyrrolidinium ionic liquid at 25 degrees C. The Kerr-gated emission and time-correlated single-photon-counting techniques were used to measure spectral dynamics occurring over the time ranges of 100 fs-200 ps and 50 ps-5 ns, respectively, and a combination of data sets from these two techniques enabled observation of the complete solvation response. Observed response functions were found to be biphasic, consisting of a sub-picosecond component of modest (10-20%) amplitude and a dominant slower component relaxing over times of a few picoseconds to several nanoseconds. The faster component could be correlated to inertial characteristics of the constituent ions, and the slower component to solvent viscosity. Dielectric continuum calculations of the sort previously used to predict solvation dynamics in dipolar liquids were shown to work poorly for predicting the response in these ionic liquids.