A Miniature Battery-free Remote Sensing System for Real-Time Monitoring of Gastroesophageal Reflux Disease

Gastroesophageal reflux disease (GERD) refers to a condition that the reflux of stomach contents causes symptoms to patients (Figure 1A). Studies show that GERD has high prevalence around the world. It was estimated that GERD prevalence was ~23% in America, ~17% in Europe, ~5% in East Asia, ~21% in the Middle East, and ~12% in Australia (Figure 1B). The numbers are expected to increase, especially in North America and East Asia [1-2]. In Hong Kong, 8.9% of Hong Kong people suffer from GERD symptoms at least monthly [3]. GERD can irritate esophagus, causing pain, inflammation and ulceration. Complications include esophageal strictures and Barrett’s esophagus [4]. In some serious cases, esophageal cancer can be developed which was the ninth fatal cancer in Hong Kong [5]. GERD may also induce high levels of anxiety and depression on patients, substantially decreasing their quality of life.

Figure 1: Background of Gastroesophageal Reflux Disease (GERD).

(A) Illustration of Gastroesophageal Reflux (GERD). (B) Prevalence of GERD around the world [1-2].

Figure 2: Traditional esophageal pH monitoring method. It is one of the current gold standards for diagnosis of GERD [6].

(A) pH catheter which passes a thin catheter through nose, down into esophagus [7-8]. (B) Wireless pH monitoring capsule [9-10].

In clinic, esophageal pH monitoring is accepted as the gold standard for diagnosis of GERD as it is the most objective method to detect reflux episodes [6]. It can also be used to monitor the effect of medical or surgical treatment on GERD patients. The current esophageal pH monitoring is an outpatient procedure to directly measure and record the pH or amount of acid that flows into esophagus from stomach in a given period of time. To date, one of the pH monitoring method is using a pH catheter, which passes a thin catheter through nose, down into esophagus (Figure 2A) [7-8]. The catheter is connected to a monitoring device on patient’s belt and patient is discharged and stay at home for 24-hour monitoring. This catheter method causes nasal and pharyngeal discomfort. Therefore, patients may reduce their activity and eating, resulting less acid reflux episodes and a false negative test. Alternatively, another method is wireless pH monitoring, which attaches a capsule to esophageal wall via endoscope (Figure 2B) [9- 10]. The capsule can send pH data to an external recorder wirelessly for 48 to 96 hours. Although the catheter-free design offers less discomfort and extended monitoring time features, it is highly expected to have a miniature device with a longer pH monitoring period in esophagus by the medical doctors. In addition, toxic materials/chemicals from the battery may leak out and cause unpredictable injury in patient’s digestive system.


This project developed a miniature battery-free remote sensing system, namely RefluxChip, with extended detection period for real-time monitoring of GERD in a non-invasive and inexpensive fashion (Fig. 3). Similar to a lemon battery, RefluxChip is powered by the redox reaction between the electrodes and refluxed gastric acid from the patient’s stomach. The harvested energy is used to power the RF transmitter. An external signal recorder detects the signal and records the acid reflux episode. Battery-free design of RefluxChip offers extended detection times, but also a sensing device that can avoid toxic materials from conventional batteries. Moreover, without the constraint of the batteries, the small size of RefluxChip enables easy-to-operate deployment via endoscopic delivery. With such advantages, the RefluxChip system is expected to provide a better strategy that can clinically benefit patients with GERD in a non-invasive fashion.

Figure 3: Overall design of RefluxChip

Figure 4: Preclinical test of the RefluxChip on in vivo pig model.

Table 1. Comparison of RefluxChip system with traditional esophageal pH monitoring methods.

RefluxChip system can significantly increase the monitoring time to 1 week time via the unique battery-free and body-fluid-based energy harvesting design. The battery-free design can also avoid toxic materials from battery, making it a safer implantable device. Moreover, RefluxChip system has integrated and home-designed circuit by combining acid detection with self-powering, which reduces its size and the cost of fabrication. It is also designed to be attached to esophageal wall by commercial EndoClip. No additional attachment device is needed, which makes it more cost-effective.

Research Team


Prof. Li ZHANG

Prof. Li Zhang is a professor in the Department of Mechanical and Automation Engineering (MAE) and a professor by Courtesy in the Department of Surgery, at The Chinese University of Hong Kong (CUHK). He is also a director of the Shenzhen Institutes of Advanced Technology (SIAT) of the Chinese Academy of Sciences (CAS) – CUHK Joint Laboratory of Robotics and Intelligent Systems. Dr. Zhang received his Ph.D. degree from the University of Basel, Switzerland. During his Ph.D. research, he was also with the laboratory for micro- and nanotechnology (LMN), Paul Scherrer Institute (PSI). Before he joined CUHK, he worked in Prof. Bradley Nelson’s group as a postdoc and then as a senior scientist and lecturer in the Institute of Robotics and Intelligent Systems, Swiss Federal Institute of Technology (ETH) Zurich, Switzerland. Dr. Zhang’s main research interests include miniature robots and devices, milli-/micro-/nanorobotics and their biomedical applications.

Prof. Philip W.Y. CHIU

Prof Philip W.Y. CHIU is currently Professor, Honorary Consultant and Head of Division of Upper Gastrointestinal and Metabolic Surgery, Department of Surgery, Prince of Wales Hospital; Director of Multi-Scale Medical Robotics Center; Director of CUHK Chow Yuk Ho Technology Center for Innovative Medicine and Associate Dean (External Affairs), Faculty of Medicine, The Chinese University of Hong Kong. His research interests include esophageal cancer management, minimally invasive and robotic esophagectomy, novel endoscopic technologies for diagnosis of early GI cancers, endoscopic surgery as well as robotics for endoluminal surgery. Prof. Chiu is first in Hong Kong to perform endoscopic submucosal dissection (ESD) for treatment of early GI cancers in 2004 and Per-oral Endoscopic Myotomy (P.O.E.M.) in 2010. In 2011 he pioneered world first robotic gastric ESD, followed by world first robotic colorectal ESD in 2020.

Prof. Kai Fung CHAN

Prof. Kai Fung CHAN’s research interests include medical miniature devices, micro-/nanorobotics, and translational medicine. His research interests are (1) Miniature medical devices for the in vivo diagnosis and treatment of gastrointestinal diseases; (2) Microrobotic sensing platforms for automated pathogen sensing; (3) Micro-/nanorobotics for minimally invasive endoluminal intervention; and (4) the corresponding translational research. His research on microrobotic platforms for biomedical applications was published in Science Robotics in 2021 and Advanced Materials in 2022. One of them was highlighted in Nature Spotlight and many local media. He has 7+year of experience in biomedical engineering research and preclinical studies.

Mr. Chong ZHANG

Mr. ZHANG Chong received his M.Sc. degree in Mechanical & Automation Engineering from CUHK in 2019 and his B.Eng. degree from Beijing Forestry University in 2017. His main research interests focus on ingestible electronics for non-invasive diagnosis and treatment.