A novel microelectronic ?pill? has been developed for in situ studies of the gastro intestinal tract, combining mi-crosensors and integrated circuits with system-level integrationtechnology. The measurement parameters include real-timeremote recording of temperature, pH, conductivity, and dissolvedoxygen. The unit comprises an outer biocompatible capsuleencasing four microsensors, a control chip, a discrete componentradio transmitter, and two silver oxide cells (the latter providingan operating time of 40 h at the rated power consumption of 12.1mW). The sensors were fabricated on two separate silicon chipslocated at the front end of the capsule. The robust nature of thepill makes it adaptable for use in a variety of environments relatedto biomedical and industrial applications.
INTRODUCTION
?????????????????????????????????? The invention of the transistor enabled the first ra-diotelemetry capsules, which utilized simple circuits for in vivo telemetric studies of the gastro-intestinal (GI) tract.These units could only transmit from a single sensor channel,and were difficult to assemble due to the use of discretecomponents. The measurement parameters consisted of either temperature, pH or pressure, and the first attemptsof conducting real-time noninvasive physiological measurements suffered from poor reliability, low sensitivity, and short lifetimes of the devices. The first successful pH gut profiles were achieved in 1972,with subsequent improvements in sensitivity and lifetime.Single-channel radiotelemetry capsules have since been applied for the detection of disease and abnormalities in the GI tract where restricted access prevents the use of traditional endoscopy.Most radiotelemetry capsules utilize laboratory type sensors such as glass pH electrodes,resistance thermometers,or moving inductive coils as pressure transducers. The relatively large size of these sensors limits the functional complexity of the pill for a given size of capsule.Adapting existing semiconductor fabrication technologies to sensor development has enabled the production of highly functional units for data collection, while the exploitation of integrated circuitry for sensor control, signal conditioning,and wireless transmission has extended the concept of single-channel radiotelemetry to remote distributed sensing from microelectronic pills.
Our current research on sensor integration and onboard data processing has, therefore, focused on the development of microsystems capable of performing simultaneous multi parameter physiological analysis.The technology has a range of applications in the detection of disease and abnormalities in medical research.The overall aim has been to deliver enhanced functionality,reduced size and power consumption,through system-level integration on a common integrated circuit platform comprising sensors,analog and digital signal processing,and signal transmission.In this paper,we present a novel analytical microsystem which incorporates a four-channel microsensor array forreal-time determination of temperature,pH,conductivity and oxygen.The sensors were fabricated using electron beam and photolithographic pattern integration,and were controlled by an application specific integrated circuit (ASIC), which sampled the data with 10-bit resolution prior to communication off chip as a single inter leaved data stream. An integrated radiotransmitter sends the signal to a local receiver (base station),prior to data acquisition on a computer.Real-time wireless data transmission is presented from a model.
??????????????????????? In Vitro experimental setup,for the first time Details of the sensors are provided in more detail later, but included:a silicon diode to measure the body core temperature,while also compensating for temperature induced signal changes in the other sensors;an ion-selective field effect transistor,ISFET to measure pH;a pair of direct contact gold electrodes to measure conductivity and a three-electrode electrochemical cell, to detect the level of dissolved oxygen in solution. All of these measurements will, in the future, beused to perform.
In Vivo physiological analysis of the GI-tract.For example, temperature sensors will not only be used to measure changes in the body core temperature, but may also identify local changes associated with tissue inflammation and ul-cers. Likewise, the pH sensor may be used for the determina-tion of the presence of pathological conditions associated with abnormal pH levels, particularly those associated with pancreatic disease and hypertension, inflammatory bowel disease, theactivity of fermenting bacteria, the level of acid excretion, reflux to the oesophagus,and the effect of GI specific drugs ontarget organs.
The conductivity sensor will be used to monitor the contents of the GI tract by measuring water and salt absorption,bile secretion and the breakdown of organic components into charged colloids. Finally, the oxygen sensor will measure the oxygen gradient from the proximal to the distal GI tract.This will, in future enable a variety of syndromes to be investigated including the growth of aerobic bacteria or bacterial infection concomitant with low oxygen tension,as well as the role of oxygen in the formation of radicals causing cellular injury and pathophysiological conditions (inflammation and gastric ulcer-ation).The implementation of a generic oxygen sensor will alsoenable the development of first generation enzyme linked am-perometric biosensors,thus greatly extending the range of future applications to include,e.g.,glucose and lactate sensing,as well as immunosensing protocol.
???????????????????? Microelectronic pill,microsensor integration mobile analytical microsystem, multilayer silicon fabrication,radiotelemetry,remote? in situ measurements.
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