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A continuously recording, impedimetric thermal liquid flow sensor fabricated on a Parylene C thin film substrate is presented for the first time. The sensing concept, inspired by hot-film anemometry, includes an additional upstream unheated reference electrode pair which enabled attenuation of environmental drift in impedance by more than 5 ×. This sensor design and transduction approach was motivated by the need for an alternative to traditional hot-film anemometers for in vivo applications. An analytical model was developed to describe the axial fluid temperature surrounding the impedimetric sensor and its effect on solution conductivity. The impact of heater power was modeled and matched with experimental data; similar analysis was conducted for other parameters including channel height, ambient temperature, and electrolyte concentration. The sensor achieved a 2σ resolution of 17 μL/min over the range 43–200 μL/min. The models and fabricated device significantly expand our understanding of thermal impedimetric flow sensing. [2020-0357] [ABSTRACT FROM AUTHOR]

A novel temperature transduction method using the high-frequency electrochemical impedance between a pair of microelectrodes exposed to aqueous solution is reported. The solution resistance of an aqueous ionic solution is highly temperature dependent, and the electrochemical impedance between two microelectrodes is dominated by solution resistance when measured at the appropriate frequency. Therefore, precise measurements of electrochemical impedance at the proper frequency in a two-electrode system can be used to transduce solution temperature. To demonstrate this method, a temperature sensor composed of two thin-film platinum electrodes on a freestanding Parylene C substrate was designed and fabricated. A platinum resistance temperature detector was co-fabricated to provide a simple means of benchmarking against an existing standard. Transduction via electrochemical impedance was achieved by measuring the real part of impedance at the frequency where phase was minimized. Fluid temperature was transduced between 15°C and 50°C with high sensitivity (−1.21%/°C) and resolution (0.02°C). A $4\times $ improvement in sensitivity and resolution over the conventional platinum resistance temperature detector was achieved. The sensor design described here features flexible construction with inert materials which facilitates future use in biomedical or microfluidic applications. [2019-0190] [ABSTRACT FROM AUTHOR]

A novel electrochemical-thermal flow sensor was developed for use in physiological liquids. The sensor was constructed out of a platinum resistive heater and platinum sensing electrodes on a Parylene C substrate, rendering it flexible and fully biocompatible. During heating, changes in electrochemical impedance across the sensing electrodes were used to detect changes in temperature, and highly sensitive flow measurements were achieved with overheat temperatures of only 1 °C. The sensor’s biocompatibility and low overheat temperature make it an ideal candidate for chronic in vivo applications. [2016-0170] [ABSTRACT FROM PUBLISHER]

A novel pressure transducer concept is introduced in which external pressure variations induce changes in the volume of a trapped microbubble ( \mu \textB ) in an electrolyte solution. These volumetric changes are monitored by electrochemical impedance-based measurements and may be used for pressure tracking applications. Microbubbles are nucleated on-demand by electrolysis within a confinement chamber with high precision (measured size RSD $\sim 1$ %). This pressure transducer concept was developed specifically for operation in liquid environments and features biocompatible construction, small footprint (<0.1 mm2), and low power consumption (<1 nW). This combination of features is ideal for in vivo pressure monitoring applications. [2015-0203] [ABSTRACT FROM PUBLISHER]

To investigate the mechanical interactions between the implanted cortical multielectrode probes and brain tissue, a Parylene C-based electrochemical-microelectromechanical systems force sensor array was developed. The array consists of seven linearly distributed sensor units arranged along the length of a flexible Parylene C microchannel. The seven sensor units are formed by eight fluidically coupled and adjacent platinum electrode pairs enclosed within the microchannel. Deformation of the top surface of the mechanically compliant microchannel changes the volumetric conduction path between the pairs of sensing electrodes, and therefore, the measured electrochemical impedance, which is proportional to the magnitude of the contacting force. Each sensor unit demonstrated a linear response from 0 to 60 mN with a sensitivity of 0.13 ± 0.01 percentage change in impedance/ \mu \textN (%/ \mu \textN ; mean ± SE, n = 6 ). The sensor arrays were mounted onto a ceramic intracortical probe and inserted into the tissue phantoms to verify in situ functionality and assess interfacial probe mechanics. Probe surface force distribution was measured under various insertion speeds and the results indicated that interfacial forces are distributed nonuniformly along the probe shaft length, concentrating within the first 1 mm of the advancing probe tip. Faster insertion speeds were also found to decrease the magnitude of the interfacial forces, suggesting that the tissue strain during cortical implantation may be minimized through appropriate selection of the insertion speed.[2014-0320] [ABSTRACT FROM PUBLISHER]

The electrochemical (EC) properties of microelectrodes on flexible polymer substrates can vary as a result of microfabrication and postfabrication processes. These in turn may impact the chronic recording performance of such electrodes. In this paper, electrochemical techniques were utilized for the preparation and nonbiological evaluation of microfabricated flexible neural probes consisting of platinum electrode recording sites supported and insulated by Parylene C. The polymer substrate mitigates the mechanical mismatch between neural tissue and the probe. In addition, the thermoplastic nature of the polymer enables the probe to be shaped postfabrication using a thermoforming technique to impart a unique 3-D structure that further promotes tissue integration and supports the use of bioactive coatings. The EC techniques provided a simple means to clean electrode surfaces (80.2% decrease in 1-kHz impedance), identify functional devices, and evaluate their EC properties prior to implant. Both electrochemical impedance spectroscopy and cyclic voltammetry measurements were performed on electrode sites following fabrication, cleaning, mechanical manipulation for assembly, thermoforming, and sterilization. The results reveal in some cases changes in EC properties. Although changes following thermoforming did not impact the ability to acquire electrophysiological recordings, further investigation with additional tools is required to elucidate the exact nature of the structural and EC changes resulting in the observed increase in impedance and reduction in electrode surface area following thermoforming. [2014-0378] [ABSTRACT FROM PUBLISHER]

We report on the use of electrochemical impedance (EI) as the basis for force transduction in Parylene-based microdevices. Electrolyte-filled microstructures were realized for extremely sensitive contact-force detection (10 mN range, \pm0.023 mN resolution) enabled by EI-based transduction and are a promising platform for next-generation biomedical sensing technology. The design, fabrication, and characterization of Parylene-based electrochemical-MEMS (EC-MEMS) devices capable of microNewton contact-mode force measurement are presented and discussed.\hfill[2011-0040] [ABSTRACT FROM AUTHOR]

We report the design, fabrication, and characterization of electrochemical microelectromechanical systems (EC-MEMS) devices featuring encapsulated fluid as the basis for transduction. Parylene microstructures, including discrete chambers (square or circular geometry), are utilized as physical transducers for electrochemically mediated liquid impedance transduction of physical phenomenon such as contact and force. Parylene-based EC-MEMS technologies uniquely leverage advantages in size (<500\ \mu\m diameter), packaging (no hermetic packaging necessary), power (nanowatts to microwatts), and flexibility to address the physical sensing requirements of in vivo applications. Robust EC impedance (EI) sensor responses (up to 20% from base-line) and discrimination of 200-nm chamber deflections were possible using the EI transduction technique. Additional transducer configurations enabling electrolysis-based out-of-plane actuation and biomimetic mechanotransduction in microfluidic channels are also presented. \hfill[2010-0157] [ABSTRACT FROM AUTHOR]