Tailoring grating strip widths for optimizing infrared absorption signals of an adsorbed molecular monolayer

Metal structures with resonances in the mid-infrared spectral range enable an increased sensitivity for detecting molecular vibrational signals. 1D gold strip gratings have already proven potential in surface-enhanced infrared absorption (SEIRA) experiments, as grating resonances and local electric field enhancement can be spectrally tuned by changing the grating period. Here, we identify the grating strip width as another important design parameter, which is investigated for further optimization of molecular absorption signal enhancement in SEIRA experiments. Previous literature used gratings to increase light absorption in relatively thick polymer layers. Here, we demonstrate the capability of gold strip gratings fabricated on a CaF₂ substrate to enhance the CH₂ vibrational modes of a thiol-based monolayer of MHDA. An optimal choice of the strip width w = 1.33 μm enables a maximum vibrational signal enhancement factor of around 84, when normalized to microscopic GIR measurements of an MHDA monolayer on an extended gold surface. Numerical simulations demonstrate the broadband local field enhancement of gold strip gratings, which are suitable for enhancing multiple vibrational modes in a large hot-spot volume.

Note: Characterization of electrode materials for dielectric spectroscopy

When measuring the dielectric properties of aqueous samples, the impedance of the electrode/sample interface can limit low frequency measurements. The electrode polarization problem can be reduced by increasing the effective surface area of the electrodes. In this work, impedance spectroscopy was used to characterize and compare three different electrode surfaces that can be used to mitigate this effect: platinum black, iridium oxide, and [polypyrrole/poly(styrenesulphonate)] (PPy/PSS) conducting polymer. All three materials were directly compared with a bright platinum electrode. Equivalent circuit models were used to extract the increase in the effective surface area of the electrodes: platinum black, iridium oxide and PPy/PSS increase the effective capacitance of the electrode by factors of approximately 240, 75, and 790, respectively. The practical aspects of all electrode materials are discussed. These results suggest that iridium oxide and PPy/PSS are good alternatives to the commonly used platinum black, which is prone to mechanical damage (scratches) and is potentially toxic to cells.

Transponder system for non-invasive measurement of intravascular pressure

Monitoring of blood pressure and pulse rate offers diagnostical and therapeutical opportunities in hypertension disease and arrhythmia, respectively. This paper presents an intravascular pressure monitoring system consisting of an implantable silicone capsule, which can be placed in an arterial system via a catheter. The capsule contains a pressure sensor and signal conditioning circuits for wireless data and energy transfer using 6.78 MHz transponder technology.

Vascular capsule for telemetric monitoring of blood pressure

PURPOSE

Development and experimental evaluation of an intravascular monitoring system for telemetric measurement of blood pressure and heart rate.

MATERIALS AND METHODS

The monitoring system consists of an implantable silicone capsule (diameter 2.3 mm), containing a dedicated microchip with pressure sensors and signal-processing circuits as well as an antenna for wireless data and energy transfer using 6.78 MHz transponder technology. Three self-expanding legs at one end of the capsule served as a mechanism to lock the capsule at an arterial branch. A flow model, driven by a ventricular assist system, was used for testing and optimizing the implantation equipment, for checking the anchoring mechanism and for ensuring transmission of the measured pressure to the readout unit. In-vivo experiments were performed in 8 minipigs (weight 25 to 30 kg), with three capsules placed in each minipig via the femoral artery using a dedicated 8-F sheath/pusher system. Follow-up was by CT angiography for up to 6 months after implantation.

RESULTS

Flow model tests revealed a maximum deviation of pressure and heart rate measurements of 5% from the reference measurements. Signal transmission was reliable over a distance of 3 to 4 cm. Fluoroscopically guided in-vivo implantation of the capsules was simple and straightforward. In arteries with a diameter of 5 to 6 mm, the capsules were permanently fixed with one or two legs interlocked in side branches and without occlusion within 6 months. Three capsules developed a small non-occlusive appositional thrombus attached to the downstream (leg) part of the capsule.

CONCLUSION

Our in-vitro and in-vivo experiments demonstrate the feasibility of wireless transmission from a capsule with a sufficient resolution of the sensor output signals to determine blood pressure and pulse rate. As long as the vessel diameter is wide enough, arterial fixation of the capsule does not induce thrombotic occlusion of the parent artery. With respect to future clinical applications, further refinements of the transmission technology are needed to extend the transmission distance between capsule and reader antenna. The technology of intelligent implants has further implications, such as monitoring of other physiological parameters, and the design of a control loop, which may be used for therapeutic feedback.

Development of a completely encapsulated intraocular pressure sensor

A completely encapsulated intraocular pressure (IOP) sensor equipped with telemetric signal and energy transfer is introduced integrated into a silicone disc for implantation into the eye. After implantation into enucleated pig eyes and into rabbit eyes in vivo, the IOP was recorded and compared to established techniques of IOP measurement. Pressure chamber tests showed that the sensor functioned correctly after biocompatible encapsulation in polydimethylsiloxane. In vivo and in vitro tests in rabbit and pig eyes demonstrated that the implanted system worked with the same precision as established techniques for IOP determination. The correlation between the measurements with the implanted device and pneumotonometry in several experiments was between 0.9 and 0.99. This device serves as a functioning model for the realization of a telemetric IOP sensor for integration into an artificial intraocular lens. Such a device will open new perspectives, not only in the management of glaucoma, but also in basic research for mechanisms of glaucoma.

Miniaturized ion-selective chip electrode for sensor application

The performance of miniaturized potentiometric cells, with multilayer, planar ion-selective sensors in aqueous electrolyte solutions, human serum, urine, and whole blood, is presented. The basic steps of the fabrication with silicon technology are summarized. The effect of the contact surface between the internal reference system and the ion-sensitive membrane on the analytical characteristics of potassium- and calcium-sensitive sensors is studied. Silicone rubber-, high molecular weight PVC-, carboxylated PVC and aliphatic polyurethane (Tecoflex)-based solvent polymeric membranes were dispensed into anisotropically etched wells on silicon wafers, and the resulted planar sensors were tested in terms of their ion sensitivity (slopes of the cell voltage-pK or pCa calibration curves), long-term stability, and reproducibility. For the assay of potassium in whole blood, the miniaturized potentiometric cell was built in a flow-through manifold. To achieve the required precision, the flow conditions were optimized and the sensors calibrated periodically. The results prove the feasibility of the new sensor design and satisfy the particularly difficult requirements for the analysis of biological samples.