An Ingestible Electronic Pill for Real Time Analytical Measurements of the Gastro - Intestinal Tract
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An Ingestible Electronic Pill for Real Time Analytical Measurements of the Gastro - Intestinal Tract
AN INGESTIBLE ELECTRONIC PILL FOR REAL TIME
ANALYTICAL MEASUREMENTS OF THE GASTRO-
INTESTINAL TRACT
Erik A. Johannessen1, Tong-Boon Tang2, Lei Wang1, Lili Cui1, Mansour
Ah mad ian2, Nizamettin Aydin2, Alexandros Astaras2, Alan F. Murray2, Brian
W. Flynn2, Tugrul Aslan2, Steve P. Beaumont3, David R. S. Cumming1 and
Jonathan M. Cooper1.
1Department of Electrical Engineering, The University of Glasgow, UK.
2Department of Electrical Engineering, The University of Edinburgh, UK.
3Institute for System Level Integration, The ALBA Centre, Livingston, UK.
Abstract
A state-of-the-art electronic “pill” has been developed for in situ studies of the gastro-
intestinal (GI) tract using integrated circuit and system level integration technologies.
The measurement parameters include real time analysis of temperature, pH, conductivity
and dissolved oxygen.
Keywords: ingestible pill, sensor array, microchip control, wireless communication
1. Introduction
Ingestible analytical microsystems have extended the application of lab-on-a-chip
devices to environments with restricted access [1]. There is now a great potential in
developing non invasive microelectronic pills capable of monitoring physiological
processes in situ for the detection of disease and abnormalities in medical research.
The device comprises 4 microelectronic sensors. A microfabricated silicon diode
measures the body core temperature whilst an ISFET sensor [2] measures local pH of
the stomach acid and the intestine. A pair of direct contact gold electrodes measures the
conductivity of, and indirectly, the contents of the stomach. The fourth sensor consists
of a three-electrode electrochemical cell [3], which is used to detect the level of
dissolved oxygen and to identify the activity of aerobic bacteria in the small and large
intestine. All the sensors are controlled by an application specific integrated circuit
(ASIC), which sample the data at a resolution of 8 bit prior to communication off chip
as a single interleaved data stream.
2. Experimental
The electronic pill comprise a biocompatible capsule, which consists of a chemically
resistant polyether-terketone (PEEK) coating, the four microfabricated sensors, the
ASIC control chip and a discrete component radio transmitter (Fig. 1). The unit is
powered by two SR44 Ag2O batteries (3.1 V), which provides an operating time of 35
hours at the rated power consumption of 15 mW.
The sensors were fabricated on two separate 5x 5 mm2 silicon chips located at the
front end of the capsule. The temperature sensor is embedded in the substrate, whereas
the conductivity sensor is directly exposed to the surroundings. The pH and oxygen
sensors were enclosed in two separate 8 nL electrolyte chambers containing a 0.1M
KOH solution retained in a 0.2 % calcium alginate gel. The electrolyte maintains a
stable potential of the integrated Ag/AgCl reference electrodes used by the two sensors.
The oxygen and pH sensor are covered by a 12 µm thick film of teflon and nafion
respectively, and protected by a 15 µm thick dialysis membrane of polycarbonate.
The signals were conditioned by the ASIC and then transmitted to a local receiver
(base