Wen Ding Huang

A Passive Radio-Frequency pH-Sensing Tag for Wireless Food-Quality Monitoring

We present a new method, suitable for food quality management by wirelessly monitoring pH level changes in food with a flexible pH sensor embedded in a batteryless radio-frequency (RF) transponder. The wireless sensor tag includes a flexible pH sensor based on miniature iridium oxide (IrOx) and silver chloride (AgCl) sensing electrodes integrated on a deformable substrate, and batteryless wireless communication circuitry. The sensor tag and reader system is designed to achieve convenient, long-term, and on-demand wireless in situ monitoring of food quality, especially for large-quantity applications and continuous monitoring from place of production to retail stores. Low-cost IrOx sol-gel fabrication process was applied on polymeric substrates to form the flexible sensing films, and a sensitivity of -49.7 mV/pH was achieved. Inducting coupling provides electromagnetic energy from the reader to drive the transponder circuits that retransmit the sensor-data modulated signals back to the reader. The electrochemical potential created by the IrOx/AgCl sensing electrodes is converted to a modulated frequency and the system achieves a sensitivity of 633 Hz/pH. The wireless pH sensing system was tested for in situ monitoring of the spoilage processes in fish meats continuously for over 18 h. The feasibility of wirelessly monitoring pH values in fish meats that could be used to identify spoilage remotely has been demonstrated.

An endoscopic wireless gastrostimulator (with video)

BACKGROUND Gastric electric stimulation (GES) at a high-frequency, low-energy setting is an option for treating refractory gastroparesis. The currently available commercial stimulator, the Enterra neurostimulator (Medtronic Inc, Minneapolis, MN), however, requires surgical implantation and is powered by a nonrechargeable battery. OBJECTIVE To develop and test a miniature wireless GES device for endoscopic implantation in an experimental model. DESIGN In-vivo gastric signals were recorded and measured in a nonsurvival swine model (n = 2; 110-lb animals). INTERVENTION An endoscopically placed, wireless GES device was inserted into the stomach through an overtube; the two GES electrodes were endoscopically attached to the gastric mucosa and secured with endoclips to permit stimulation. MAIN OUTCOME MEASUREMENTS Stable electrogastrogram measures were observed during GES stimulation. RESULTS Electrogastrogram recordings demonstrated that gastric slow waves became more regular and of constant amplitudes when stomach tissues were stimulated, in comparison with no stimulation. The frequency-to-amplitude ratio also changed significantly with stimulation. LIMITATION Nonsurvival pig studies. CONCLUSION Gastric electric stimulation is feasible by our endoscopically implanted, wireless GES device.

An implantable batteryless wireless impedance sensor for gastroesophageal reflux diagnosis

A new method for long term monitoring of gastroesophageal reflux is presented. The impedance of the reflux in the esophagus can be determined remotely without the need of a battery in the sensor implant. The implant includes an energy harvesting circuit, sensing electrodes, an antenna and an impedance to frequency converter. An external reader provides power to the implant and measures the impedance values simultaneously. A prototype with an overall size of 0.5×1×3.1cm3 was made with a printed circuit board and discrete components, and packaged in polydimethylsiloxane. In vivo experiments were conducted in pig cadavers. The results show good correlation between impedance and pH values of the acid solutions flushed into the esophagus, and good signal-to-noise ratios with the transducer inside the body. The impedance sensor can detect nonacid materials due to the frequency shift differences between air and solutions. The batteryless wireless impedance sensor is able to detect every reflux episode, either acid or non-acid, which provides more accurate diagnosis for the gastroesophageal reflux disease.

Sol-Gel Iridium Oxide-Based pH Sensor Array on Flexible Polyimide Substrate

Iridium oxide pH sensing film is demonstrated with wide pH-sensing ranges, high durability, and small drifts in potentials. Using sol-gel process, a lower fabrication cost and less labor-intensive method, to deposit iridium oxide thin films for pH sensing is reported previously by our group with expected advantages. In this paper, we fabricate and test pH sensing characteristics of 4 × 4 anhydrous iridium oxide thin-film electrode arrays on flexible substrates. The sensors in arrays exhibit Nernstian potential responses in the range of 57.0-63.4 mV/pH. Stability, repeatability, and hysteresis effects of the pH sensor arrays are examined. A multichannel recording system is built to demonstrate the functionality of the pH sensor arrays in monitoring spatial and temporal pH changes across a surface.

Development of innovative techniques for the endoscopic implantation and securing of a novel, wireless, miniature gastrostimulator (with videos)

BACKGROUND Gastric stimulation via high-frequency, low-energy pulses can provide an effective treatment for gastric dysmotility; however, the current commercially available device requires surgical implantation for long-term stimulation and is powered by a nonrechargeable battery. OBJECTIVE To test and describe endoscopic implantation techniques and testing of stimulation of a novel, wireless, batteryless, gastric electrical stimulation (GES) device. DESIGN Endoscopic gastric implantation techniques were implemented, and in vivo gastric signals were recorded and measured in a non-survival swine model (n = 2; 50-kg animals). INTERVENTION Five novel endoscopic gastric implantation techniques and stimulation of a novel, wireless, batteryless, GES device were tested on a non-survival swine model. MAIN OUTCOME MEASUREMENTS Feasibility of 5 new endoscopic gastric implantation techniques of the novel, miniature, batteryless, wireless GES device while recording and measurement of in vivo gastric signals. RESULTS All 5 of the novel endoscopic techniques permitted insertion and securing of the miniaturized gastrostimulator. By the help of these methods and miniaturization of the gastrostimulator, successful GES could be provided without any surgery. The metallic clip attachment was restricted to the mucosal surface, whereas the prototype tacks, prototype spring coils, percutaneous endoscopic gastrostomy wires/T-tag fasteners, and submucosal pocket endoscopic implantation methods attach the stimulator near transmurally or transmurally to the stomach. They allow more secure device attachment with optimal stimulation depth. LIMITATIONS Non-survival pig studies. CONCLUSION These 5 techniques have the potential to augment the utility of GES as a treatment alternative, to provide an important prototype for other dysmotility treatment paradigms, and to yield insights for new technological interfaces between non-invasiveness and surgery.

Development of an Implanted RFID Impedance Sensor for Detecting Gastroesophageal Reflux

A new method to detect gastroesophageal reflux is presented. Based on passive RFID principles, the impedance of the refluxate can be determined. We have designed and fabricated planar coils integrated with electrodes on flexible substrates using standard photolithography processes. The device can be implanted in the esophagus using currently available clinical techniques. In vitro experiments with simulated stomach acid were conducted. An approach to integrate the sensor with RFID systems is proposed. This device can help diagnose gastroesophageal reflux disease effectively.

A Simple Wireless Batteryless Sensing Platform for Resistive and Capacitive Sensors

In this paper, a simple wireless platform to transduce data from sensors without the need for a battery in the sensors is introduced. The sensor can be either resistor-or capacitor-based. The sensing systems adapt RFID operation principles including a reader and a transponder. Our platform is fully analog and contains few components making it easy to implement with existing ICs and sensors. The platform for temperature sensing has been demonstrated. The device includes a 1times2.5 cm2 coil antenna and a thermistor. The read range is 4 cm using a 6times6 cm2 reader antenna powered at 970 kHz. A temperature range of 5-90degC is monitored resulting in read frequencies from 6 to 10 kHz.

A wireless sensor for detecting gastroesophageal reflux

In this paper, we propose a new method to detect gastroesophageal reflux wirelessly. Based on passive telemetry using inductive links, impedance of the refluxate can be determined. We have designed and fabricated planar coils integrated with electrodes on flexible substrates using standard photolithography processes. The device can be implanted in the esophagus using currently available clinical techniques. In vitro experiments were conducted by passing different acidic or non-acidic solutions onto the implanted electrodes and measuring the signal amplitudes with an external receiver. Air, drinking water and different concentrations of artificial stomach fluids were used to test the impedance sensor. System configuration, device designs, fabrication processes and measurement results will be presented in this paper.

Investigation of repeatability of sol-gel iridium oxide pH sensor on flexible substrate

In this paper, we presented the fabrication process of miniature pH sensor arrays on flexible polymer substrates. The repeatability of the sensors based on sol-gel fabrication processes was investigated. The sensor repeatability was characterized with linearity, decay time, environmental parameter control and potential stability. Similar linear responses were found in different batches of sensor arrays. Near super- Nernstian responses were measured on each sensor with slope ranges from -71.6 to -110 mV/pH within a pH range between 2 and 12. The response times were compared in different batches. Six to twenty five seconds of average decay time were shown in each sample repeatedly. Three sensors showed the close potential response in different volumes of pH buffer solution. The sensor showed good stability in each step of the titration process between pH values of 1.8 and 11.9. The peak and saturated potential values presented high correlation with pH values with minor noises. The results showed good sensitivity, stability and repeatability using the sol-gel processes for iridium-oxide pH sensors on flexible substrates.

Development of an IrOx micro pH sensor array on flexible polymer substrate

pH sensor is an essential component used in many chemical, food, and bio-material industries. Conventional glass electrodes have been used to construct pH sensors, however, have some disadvantages in specific applications. It is difficult to use glass electrodes for in vivo biomedical or food monitoring applications due to size limitation and no deformability. In this paper, we present design and fabrication processes of a miniature iridium oxide thin film pH sensor array on flexible polymer substrates. The amorphous iridium oxide thin film was used as the sensing material. A sol-gel dip-coating process of iridium oxide film was demonstrated in this paper. A super-Nernstian response has been measured on individual sensors of the array with a slope of -71.6±3 mV/pH at 25°C within the pH range between 2.83 and 11.04.