Polymer Transducers Research Articles

PCR-Free DNA Detection Using a Magnetic Bead-Supported Polymeric Transducer and Microelectromagnetic Traps

A fluorescent polymeric hybridization transducer supported on magnetic microbeads was investigated for the rapid, ultrasensitive, and sequence-specific detection of DNA. We show that the polymer derivative can be used to detect target DNA directly on magnetic particles by preparing "target-ready" microbeads grafted with the polymer and suitable DNA probes. A detection limit of approximately 200 target copies in a probed volume of 150 muL (1.4 copies/muL) was obtained for a DNA sequence specific to Candida albicans This detection scheme does not require the release of the hybridized target DNA prior to its detection or the labeling or amplification of the nucleic acids. Furthermore, we show that the fluorescence from these biosensing magnetic beads can be read while magnetically confined in a small volume by a microelectromagnetic trap, which offers the possibility of performing both the preconcentration and detection steps simultaneously on the same support. The combination of the fluorescent polymer biosensor with magnetic particle-assisted DNA preconcentration extends the application of this ultrasensitive biosensor to biological samples with complex matrixes and to integrated lab-on-a-chip platforms, where it could be used for fast multitarget DNA detection in point-of-care diagnostics and field analysis.

All-solid-state ion-selective electrodes for determining amiodarone

New all-solid-state ion-selective electrodes for determining amiodarone have been developed. A special feature of the electrode design is the presence of an intermediate polymer transducer layer between the ion-selective membrane and the metal electrode. The transducer can be made of polyaniline or specially synthesized poly(N-phenylglycine). The electrochemical characteristics of new electrodes in systems with different transducer materials have been determined. It is shown that a transducer ensures long-term stability of the electrode parameters and makes possible miniaturization of the electrode system. The proposed electrodes have been successfully used for the analysis of amiodarone tablets.

Tailoring Solution Cast Poly(3,4‐dioctyloxythiophene) Transducers for Potentiometric All‐Solid‐State Ion‐Selective Electrodes

AbstractA novel concept of tailoring potentiometric responses of all‐solid‐state ion‐selective electrodes was introduced. The effect of composition and resulting properties of the conjugated polymer transducer, placed between the electrode support and ion‐selective membrane, on analytical characteristic of obtained sensors was studied.

Effect of interferents present in the internal solution or in the conducting polymer transducer on the responses of ion-selective electrodes

The effect of interferents present on the opposite side of the Pb2+-selective membrane has been studied for both internal solution and all-solid-state sensors with a conducting polymer (CP) transducer. For interferents with moderate selectivity coefficients (sodium cations) present in the internal solution or in the CP transducer phase, super-Nernstian responses were obtained. For sensors containing strongly discriminated interferents (lithium ions), however, responses typical of conventional electrodes are observed, despite the low activity of primary ions on the opposite side of the membrane. This effect is attributed to hindered incorporation of interfering ions into the membrane, which also impairs the long term stability of the potential. Because of the relatively small absolute amounts of interferents in the transducer of all-solid-state sensors, their exchange for primary ions occurs quickly. Thus, transformation of the sensor to one with a micromolar detection limit and high potential stability is observed.

Stretched rolled electroactive polymer transducers and method of producing same

A transducer is designed and fabricated using stretched rolled electroactive polymers. The invention includes the design, fabrication, and integration of a stretched rolled actuator system with corresponding sensing, control and power subsystems. The invention presented is based on the improved performance of electroactive polymer transducers that can be achieve by prestretching the polymeric material. In this invention, the preferred stretch is maintained in a rolled configuration by introducing structural elements to the transducer. The structural elements facilitate fabrication of the transducer as well as provide a compact and efficient means of maintaining stretch and the desired boundary conditions on the electroactive polymer during operation. These conditions together are used to improve and tailor the strain response of the transducer.

High-strain ionomeric–ionic liquid electroactive actuators

Ionomeric polymers are a class of electromechanical transducer consisting of an ionomeric substrate with metal-plated electrodes. Application of a low-voltage (<5 V) across the thickness of the membrane produces controllable strain. The advantage of ionomeric polymers compared to other types of electromechanical transducers (e.g. piezoelectric polymers) is low-voltage operation, High-strain capability, and high sensitivity to motion in charge sensing mode. Two of the primary limitations of ionomeric polymers for electromechanical transducers are unstable operation in air and solvent breakdown at low-voltage. This work focuses on overcoming these limitations through the development of an ionic liquid-ionomeric composite with a tailored electrode composition that maximizes strain output. It is becoming clear that charge accumulation at the polymer-electrode interface is the key to producing high-strain in ionomeric polymer transducers. In this work, we combine a previously developed process for incorporating ionic liquids into ionomer membranes with a new method for tailoring the electrode composition. The electrode composition is studied as a function of the surface-to-volume ratio and conductivity of the metal particulates. Results demonstrate that the surface-to-volume ratio of the metal particulate is critical to increasing the capacitance of the transducer. Increased conductivity of the metal particulates produces improved response at higher frequencies (>10 Hz), but this effect is small compared to the increase in strain produced by maximizing the capacitance. Increasing capacitance produces a transducer that is able to achieve >2% strain ( ɛ) at voltage levels of ±3 V.

Direct Molecular Detection of Nucleic Acids by Fluorescence Signal Amplification

An integrated PCR-free DNA sensor, which combines a sequence-specific receptor, an optical polymeric transducer, and an intrinsic fluorescence amplification mechanism, is reported. This sensor is based on the different conformations adopted by a cationic polythiophene when electrostatically bound to ss-DNA or ds-DNA, and on the efficient and fast energy transfer between the resulting fluorescent polythiophene/ds-DNA complex and neighboring fluorophores attached to ss-DNA probes. This molecular system allows the detection of only five molecules in 3 mL of an aqueous solution, or 3 zM, in 5 min. Moreover, this work demonstrates, for the first time, the direct detection of single nucleotide polymorphisms (SNPs) from clinical samples in only a few minutes, without the need for nucleic acid amplification.

Correlation of capacitance and actuation in ionomeric polymer transducers

Ionomeric polymer transducers are electromechanical actuators fabricated from ion-exchange membranes that have been surface plated with conductive metal. In this paper we discuss a series of experiments that characterize the electromechanical actuation response of three families of ionomers: Nafion (a product of DuPont), BPSH (sulfonated poly(arylene ether sulfone)) and PATS (poly(arylene thioether sulfone)). The first polymer is commercially-available while the second and third polymers are synthesized by the direct polymerization of sulfonated monomers in our lab. The mechanical properties and actuation response of Nafion-117, BPSH, and PATS of varying ionic content are studied in the Lithium cation form. The strain response of the materials varies from 50 μ strain/V to 750 μ strain/V at 1Hz. A linear correlation was found between the strain response and the capacitance of the material. This correlation was independent of the polymer composition and the plating parameters. All of the ionomers analyzed in this work exhibited a strain-to-charge response between 9 \(\frac{\rm \mu strain}{\frac{C}{\rm m^2}}\) and 15 \(\frac{\rm \mu strain}{\frac{C}{\rm m^2}}\). Due to the fact that the low-frequency capacitance of an ionomer is strongly related to charge accumulation at the blocking electrodes, this correlation suggests a strong relationship between surface charge accumulation and mechanical deformation in ionomeric actuators.

Identification of the Nonlinear Response of Ionic Polymer Actuators using the Volterra Series

Ionic polymer transducers exhibit coupling between three physical domains: electrical, chemical, and mechanical. This coupling enables their use as both sensors and actuators. Because this phenomenon was only recently discovered, the fundamental mechanisms governing the actuation and sensing response are still open for debate. However, since ionic polymers are very compliant, low-voltage transducers have become an increasingly researched intelligent material. In this paper we aim to gain a better understanding of the physical mechanisms involved in the actuation response by studying the nonlinear harmonic distortion. The Volterra series was the chosen identification technique for its potential to extract information about the nonlinearities. Results show that the solvent appears to play a significant role in the actuation response, as evidenced by a changing distortion from different solvents.

In vivo scattering measurement of biological tissue by the use of a pyroelectric polymer transducer

We propose a new method, to our knowledge, for noninvasive scattering measurements of tissues by the use of a pyroelectric polymer transducer, poly(vinylidene fluoride trifluoroethylene) film. In this method, samples are irradiated with nanosecond, low-energy light pulses delivered from an optical fiber, and the pyroelectric signal induced by the diffuse reflectance is measured with a transducer. The signal is then converted into diffuse reflectance by use of a calibration factor. The validity of this method was confirmed by our measuring the scattering coefficient of a white acrylic resin within an accuracy of +/- 15%. We attempted to apply this method to the estimation of scattering coefficients of normal and burned skins in rats in vivo.

High Conductivity Ionic Liquid- Nafion Mat Composites for High Speed Ionic Polymer Transducers

ABSTRACTIonomeric polymer transducers consist of an ion-exchange membrane plated with conductive metal layers on the outer surfaces. Such materials are known to generate large bending strain (&gt; 9% is possible) at low applied voltages (typically less than 5 V). The main disadvantage of ionomer–ionic liquid transducers is the slow speed of response. The speed of response in such actuators has been correlated to the ionic liquid content and the conductivity of the membrane. To increase the conductivity of the transducers a Nafion™ mat is hydrated with 1-ethyl-3-methylimidazolium trifluoromethanesulfonate (EMI-Tf) ionic liquids and high surface area RuO2 electrodes are attached using the Direct Assembly Process (DAP). The Nafion™ mat is prepared from homogenous solution electrospinning. The solution is prepared by mixing 1 wt % of polyethylene oxide solution in methanol (PEO, Mol. wt 3×106) to 5 wt % Nafion 1100 solution.. The syringe needle is connected to a 15kV power supply and is placed 15cm away from the collecting drum. The measured conductivities of water hydrated Nafion electro-spun fibers are 16.8 mS/cm, which are lower than the nominal 110 mS/cm that of H+ Nafion membranes. The uptake is measured to be around 250 %wt compared to 58 %wt obtained in Nafion films. The ionic conductivity of 110 %wt swollen ionic liquids-Nafion mat composite is computed to be 0.9 mS/cm compared to 0.3 mS/cm in ionic liquid-Nafion membrane composite. The speed of response in actuators with an ionic liquid- Nafion™ mat is 1.34 %/s compared to 0.88 %/s for that in ionic liquid Nafion™ film transducers.

Variable stiffness electroactive polymer systems

The invention relates to systems that provide variable stiffness and/or variable damping using an electroactive polymer transducer. Systems described herein offer several techniques that provide variable and controlled stiffness and/or damping. A transducer may be implemented using open loop control, thereby providing simple systems that inactively deliver a desired stiffness and/or damping performance. Alternately, closed loop control techniques permit electroactive polymer transducer designs that actively adapt the stiffness and/or damping performance of a system. Further, transducers may be implemented in a device whose stiffness changes with deflection of the polymer.

Development of High-Strain and Durable Air-Stable Ionomeric Polymer Transducers(Keynote I)

Development of High-Strain and Durable Air-Stable Ionomeric Polymer Transducers(Keynote I)

Ionic liquids as stable solvents for ionic polymer transducers

Nafion™membranes are known to operate as electromechanical actuators and sensors. The transduction in the material is caused by redistribution of the mobile cations in the material, which is made possible because the material is saturated with a solvent. Typically, the solvent used is water, although its use limits the performance of these materials. This is due to the chemical breakdown of the water at relatively low operating voltages and the loss of the water to evaporation when these devices are operated in air, causing a corresponding loss of performance. In the current work, the use of highly stable ionic liquids to replace water is explored. Ionic liquids have the advantage of greater electrochemical stability than water, thus offering the possibility of higher actuation voltages for these materials. Also, ionic liquids are known to be non-volatile and therefore will not evaporate out of the polymer as water will. In this work, the use of 1-ethyl-3-methylimidazolium trifluoromethanesulfonate ionic liquid is demonstrated as a viable solvent for Nafion™polymer actuators and sensors. This ionic liquid melts at −9 °C and has an electrochemical stability Window of 4.1 V [Inorg. Chem. 35 (1996) 1168], making it a promising candidate to replace water in ionic polymer transducers. Experimental results indicate that Nafion™transducers solvated with this ionic liquid have improved staility when operated in air as compared to the same materials solvated with water, although the magnitude of the response is decreased as compared to the water samples at high frequencies. The main drawback associated with the use of ionic liquids is a reduction in the speed of the response as compared to water, although the initial results are promising and demonstrate the potential for this approach.

Clinical applications of very high frequency ultrasound in ophthalmology

The eye is ideally suited for diagnostic imaging with very high frequency (&amp;gt;35 MHz) ultrasound (VHFU) because of its peripheral location and cystic structure. VHFU allows high resolution visualization of pathologies affecting the anterior segment of the eye, including tumors, cysts, foreign bodies, and corneal pathologies. We developed a series of prototype instruments suitable for ophthalmic studies using both polymer and lithium niobate transducers, with digitization of radiofrequency echo data at up to 500 MHz. While initially using linear scan geometries, we subsequently developed an arc-shaped scan matched to the curvature of the 0.5-mm-thick cornea to circumvent the effect of specular deflection of the ultrasound beam produced by the corneas curved surface. This technique allowed us to obtain data across the entire cornea and determination of the thickness of each corneal layer, including the epithelium (approximately 50 microns in thickness) and the surgically induced interface produced in LASIK, the most common form of refractive surgery. By scanning in a series of meridians, and applying optimized signal processing strategies (deconvolution, analytic signal envelope determination), corneal pachymetric maps representing the local thickness of each layer can be generated and aid in diagnosis of surgically induced defects or refractive abnormalities.

Synthetic aperture focusing techniques in time and frequency domains for photoacoustic imaging

Synthetic aperture focusing techniques (SAFT) have been applied to B-scan images of artificial defects produced by a scanning photoacoustic probe operating under water. The probe consisted of a fibre-optic laser beam delivery system combined with a polymer (PVDF) transducer mounted at the tip of the probe for ultrasonic reception. This system had a broadband frequency response in the 1-10 MHz range. Such an integral probe was designed to optically transmit and receive near on-axis ultrasonic transients. A frequency domain synthetic aperture method was successfully applied using phantom samples to produce refined 2D images from initial B-scans. In this paper, the phantom consisted of a black nylon rectangular sample with a 1.0 mm circular defect at a depth of 5.9 mm from the surface. A comparison was made of conventional B-scan images with SAFT images. Results showed that synthetic focusing apertures, in time or frequency domains, offer better signal-to-noise ratios with improved capabilities in lateral resolution.

Fluorescent polymeric transducer for the rapid, simple, and specific detection of nucleic acids at the zeptomole level.

We report the specific detection of a few hundred molecules of genetic material using a fluorescent polythiophene biosensor. Such recognition is based on simple electrostatic interactions between a cationic polymeric optical transducer and the negatively charged nucleic acid target and can be done in less than 1 h, simply and affordably, and without any chemical reaction. This simple system is versatile enough to detect nucleic acids of various lengths, including a segment from the RNA genome of the Influenza virus.

On the relationship between the electric double layer and actuation in ionomeric polymer transducers

ABSTRACTIonic polymer transducers are soft actuators that perform large bending deflections when voltages on the order of 1–5 V are applied across their thickness. Previous work showed that actuation performance of ionic polymer transducers is strongly correlated with the capacitance due to surface charge accumulation. Increasing the capacitance of the actuator increases the motion of the charges and increases the strain produced under the application of an electric field. Ionomeric transducers consist of an ionomer, such as Nafion (a product of DuPont), sandwiched between two high surface area electrodes. An electric double layer is formed on the interface between the cathode and the adsorbed positive ions. A novel plating technique which was previously developed is used to vary the morphology of the polymer-electrode interface to investigate the parameters of importance to the formation of the electric double layer. Electromechanical transducer tests are performed as a function of electrode morphology to correlate surface charge accumulation with the deflection generated by the transducer.

MEMS Technologies for Ubiquitous Computing World: Silicon to Silicone: Stretching the Capabilities of Micromachines with Electroactive Polymers

Electroactive polymer transducers have many features that are desirable for MEMS devices. An especially attractive type of electroactive polymer is dielectric elastomer. Dielectric elastomers, transducers that couple the deformation of a rubbery polymer film to an applied electric field, show particular promise with features such as simple fabrication in a variety of size scales, high strain and energy density, high efficiency and fast speed of response, and inherent flexibility, environmental tolerance, and ruggedness. A variety of actuator configurations has been demonstrated at the small size scales needed for MEMS devices, including rolled “artificial muscle actuators, framed and bending beam actuators for efficient opto-mechanical switches, and diaphragm and thickness mode actuators for pumps and valves. The performance benefits of electroactive polymers can allow for new generations of devices in microrobotics, communications, and biotechnology. Several challenges remain for electroactive polymers, including microfabrication, integration with driving electronics, and operational lifetime.

Modeling of electromechanical charge sensing in ionic polymer transducers

A model for charge sensing due to imposed deformation in ionic polymer materials is presented. The basic concept of this model is that mechanical deformation induces charge at the surface of the polymer and produces a measureable discharge of current as the material is deformed. This discharge of current occurs when a short-circuit electrical boundary condition is applied across the material electrodes. An expression for charge density, electric field and electric potential under short-circuit conditions is developed from the electrostatic field equations. The solution for charge density is coupled with the mechanical deformation through a proportionality constant. Expressions for induced charge and current flow are then derived from the equations for electric displacement at the surface of the material. Experimental results support the basic form of the model and also demonstrate that the geometric scaling predicted in the model agrees with measured data. Analysis of the length scale predicted by the model produces qualitative agreement with previously published results but also points to the need for a greater understanding of the interfacial mechanics in the ionic polymer transducers.