Miniature pH sensor for capsule endoscopy with composite diagnosis

This paper presents a novel capsule endoscope with the synchronous acquisition of the image and pH in the gastrointestinal (GI) tract. Due to the advantages in size and response time, antimony and Ag/AgCl electrodes were used as the working and reference electrodes of the sensor respectively. Three prototypes were designed and fabricated. The first two sensors adopted the separated electrodes with different size, while the last sensor adopted the integrated ones, which was the smallest with the length of 5mm and diameter of 6.7mm. The linearity, accuracy, response time and temperature drift of three sensors were measured to assess their performance. The experimental results showed that when the temperature was fixed, the correlation coefficients were above 0.99, the error rates with buffer solution were below 3% and the response time from the neuter to strong acid was below 5 seconds. Besides, the error rate caused by the temperature drift could be reduced to the range of 1% with the compensation. Due to the advantage in size and performance, the last sensor could be integrated into the capsule endoscope.