The invention of transistor enabled the first use of radiometry capsules, which used simple circuits for the internal study of the gastro-intestinal (GI) tract. They couldn’t be used as they could transmit only from a single channel and also due to the size of the components. They also suffered from poor reliability, low sensitivity and short lifetimes of the devices. This led to the application of single-channel telemetry capsules for the detection of disease and abnormalities in the GI tract where restricted area prevented the use of traditional endoscopy. They were later modified as they had the disadvantage of using laboratory type sensors such as the glass pH electrodes, resistance thermometers, etc.
They were also of very large size. The later modification is similar to the above instrument but is smaller in size due to the application of existing semiconductor fabrication technologies. These technologies led to the formation of “MICROELECTRONIC PILL”. Microelectronic pill is basically a multichannel sensor used for remote biomedical measurements using micro technology. This is used for the real-time measurement parameters such as temperature, pH, conductivity and dissolved oxygen. The sensors are fabricated using electron beam and photolithographic pattern integration and were controlled by an application specific integrated circuit (ASIC).
When Microelectronic pill is swallowed, then it will travel through the Gastro Intestinal Tract & simultaneously perform multi parameter in situ physiological analysis After completing its mission it will come out of the body by normal bowel movement The pill is 16mm in diameter & 55mm long weighing around 5 gram It records parameters like temperature, pH, Conductivity, & Dissolved Oxygen in real time. It measures the body core temperature. Also compensates with the temperature induced signal changes in other sensors. It also identifies local changes associated with TISSUE INFLAMMATION & ULCERS.
3:TECHNOLOGY USED IN MICROELECTRONIC PILL
ION-SELECTIVE FIELD EFFECT TRANSISTOR(ISFET) The ISFET measures pH. It can reveal pathological conditions associated with abnormal pH levels These abnormalities include : Pancreatic disease Hypertension Inflammatory bowel disease The activity of fermenting bacteria The level of acid excretion Reflux of oesophagus Effect of GI specific drugs on target organs. The pair of direct contact Gold electrodes measures conductivity, by measuring the contents of water & salt absorption, bile secretion & the breakdown of organic components into charged colloids etc. in the GI tract. Since the gold has best conductivity among all the elements, Therefore it gives true value of conductivity as measured. DIRECT CONTACT GOLD ELECTRODE The three electrode electrochemical cell detects the level of dissolved oxygen in solution.
It measures the oxygen gradient from the proximal to the distal GI Tract It investigates : Growth of aerobic or bacterial infection Formation of radicals causing cellular injury & pathophysiological conditions like inflammation & Gastric ulceration. It develops generation enzymes linked with amperometric biosensors. ASIC The ASIC (Application Specific Integrated Circuit) is the control unit that connects together other components of the micro system. It contains an analogue signal –conditioning module operating the sensors, 10-bit analogue to digital (ADC) & digital to analogue (DAC) converters, & digital data processing module The temperature circuitry bias the diode at constant current so that change in temperature reflects a corresponding change in in diode voltage.
The pH ISFET sensor is biased as a simple source at constant current with the source voltage changing with threshold voltage & pH. The conductivity circuit operates at D.C. It measures the resistance across the electrode pair as an inverse function of solution conductivity. An incorporated potentiostat circuit operates the O 2 sensor with a 10 bit DAC controlling the working electrode potential w.r.t the reference Analogue signals are sequenced through a multiplexer before being digitized by ADC. ASIC & sensors consume 5.3 mW power corresponding to 1.7 mA of current. CONTROL CHIP Size of transmitter = 8 ? 5 ? 3 mm Modulation Scheme = Frequency Shift Keying (FSK) Data Transfer Rate = 1 kbps Frequency = 40.01 MHz at 20 °C Bandwidth of the signal generated 10 KHz It consumes 6.8 mW power at 2.2 mA of current.
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 I 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 5×5 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 ?m thick film of teflon and nafion respectively, and protected by a 15 ?m thick dialysis membrane of polycarbonate. The signals were conditioned by the ASIC and then transmitted to a local receiver (base station) at 40.01 MHz prior to data acquisition on a PC. The applied simplex communication link, based on a direct sequence spread spectrum communication system, can handle data from several pills at the same time.
It is used in the medical diagnosis of gestro-intestial tract disease.
The electronic pill will be further miniaturised for human ingestion by the incorporation of the transmitter on silicon and a reduction in power consumption by the implementation of a standby modus and serial bitstream data compression. The integration of radiation sensors and the application of indirect imaging technologies such as ultrasound and impedance tomography will improve the detection of tissue abnormalities and radiology treatment associated with cancer and chronic inflammation.
 Cane, C., I. Gracia, and A. Merlos, Microelectronics Journal.
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