Wireless pH measurement systems

Wireless pH measurement systems have been used in clinical studies. Unlike a standalone pH electrode, a power source, control electronics, and a signal transmitter have to be incorporated into a wireless system. Watanabe et al. [138] have reported a wireless pH sensor to record salivary pH continuously. The sensor system transmits pH data via a telemetry system for about 19 hours with a 3V lithium battery (190mAh). The error of transmitted pH data was less than 0.15 pH in the range of pH 5.0 to 9.0. 

Although they are effective, catheter-based testing systems may be limited by patient discomfort and interference with normal diet and activities. The probe can cause a great deal of discomfort and sometimes patients do not tolerate it. Wireless pH measurement devices have been used in studies to reduce these limitations and to provide prolonged, continuous recordings of esophageal pH for up to 48 hours [166, 167]. 

Rao et al. [140] described a study using a commercial pH sensitive radio-telemetry capsule (RTC) to evaluate small bowel and colonic transit time in athletes with gastrointestinal symptoms. The RTC (type 7006 Remote Control Systems, London, UK) consists of a glass electrode with an integral reference cap and battery. RF transmissions from the capsule are detected by a solid-state receiver worn on the belt of the patient. The recorder samples the pH from the capsule at 6 second intervals for a period of 24 hours. They used pH changes as an indication of the pH capsule s movement. A sharp rise in pH from around pH 2 to pH 6 indicates that the capsule has moved into the duodenum from the stomach. Then the pH progressively rises to a plateau around pH 8, which indicates that the capsule has moved into the terminal ileum. Another commercially available wireless pH sensor (Bravo) from Medtronic Inc. has been used to measure esophageal pH for a period of 48 hours and it will be discussed later. 

According to the mention above, the primary researches focused on the attempt to use the NI wireless sensor network module for V-T measurement system. And the flexible array sensor was applied to detect the response voltage for pH buffer solution, in this study. 

A. Okij, T. Yamada, H. Nakase, H. Uesugi, K. Tsubou, K. Masu, and Y. Horiike, In-vivo measurement of pH in digestive system through wireless communication, 7th Intematonal Conference on Miniaturized Chemical and Biochemical Analysts Systems, October 5-9, Squaw Valley, California (2003). 

In this design example, a capacitive technique has been exploited to measure strong acidic and basic mediums. Such sensors can be integrated within the wireless capsule to measure pH of gastric acid. This technique provides higher sensitivity and low noise readout system while maintaining simple and low-cost fabrication process. 

A wireless capsule can provide an invasive method for the diagnosis of the GI tract. The sensor systems for a wireless capsule are composed of mechanical sensors for pressure and position measurement, chemical sensors for pH, conductivity, and dissolved oxygen measurement, and biosensors for bleeding and pathogens detection. In addition to the sensor systems, interface circuits for the sensors also play an important role for the development of low-noise and low-power sensor systems. As a result, wireless capsule requires the development of a reliable, miniaturized, and integrated sensor system with high sensitivity and resolution as well as a low noise, low cost, and a low-power interface circuit system. 

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