The authors gratefully acknowledge Charles University (project GA UK No 176119) for supporting this study. This work was supported by the Charles University research program PROGRES Q 28 (Oncology).

No living animals were involved in this study. The experiment was performed on an ex vivo model consisting of a porcine esophagus and stomach. The stomach and esophagus were purchased from a local butchery as their standard product. This procedure is in accordance with Czech laws, and we prefer it because of the &#34;3R&#34; principle (Replacement, Reduction, and Refinement).
1. Fabrication of the pH sensor assembly
NOTE: Observe precautions for handling elec...

<ol>
	<li>El-Serag, H. B., Sweet, S., Winchester, C. C., Dent, J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Update+on+the+epidemiology+of+gastro-oesophageal+reflux+disease:+a+systematic+review.">Update on the epidemiology of gastro-oesophageal reflux disease: a systematic review.</a> Gut. 63 (6), 871-880 (2014).</li><li>Gyawali, C. P., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Modern+diagnosis+of+GERD:+the+Lyon+Consensus.">Modern diagnosis of GERD: the Lyon Consensus.</a> Gut. 67 (7), 1351-1362 (2018).</li><li>Cesario, S., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Diagnosis+of+GERD+in+typical+and+atypical+manifestations.">Diagnosis of GERD in typical and atypical manifestations.</a> Acta Biomedica. 89 (5), 33-39 (2018).</li><li>Sifrim, D., Gyawali, C. P. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Prolonged+wireless+pH+monitoring+or+24-hour+catheter-based+pH+impedance+monitoring:+Who,+When,+and+Why.">Prolonged wireless pH monitoring or 24-hour catheter-based pH impedance monitoring: Who, When, and Why.</a> American Journal of Gastroenterology. 115 (8), 1150-1152 (2020).</li><li>Chae, S., Richter, J. E. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Wireless+24,+48,+and+96+Hour+or+impedance+or+oropharyngeal+prolonged+pH+monitoring:+Which+test,+when,+and+why+for+GERD.">Wireless 24, 48, and 96 Hour or impedance or oropharyngeal prolonged pH monitoring: Which test, when, and why for GERD.</a> Current Gastroenterology Reports. 20 (11), 52 (2018).</li><li>Furness, J. B., Callaghan, B. P., Rivera, L. R., Cho, H. -. J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=The+enteric+nervous+system+and+gastrointestinal+innervation:+integrated+local+and+central+control.">The enteric nervous system and gastrointestinal innervation: integrated local and central control.</a> Adv Exp Med Biol. 817, 39-71 (2014).</li><li>Sanmiguel, C. P., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Effect+of+electrical+stimulation+of+the+LES+on+LES+pressure+in+a+canine+model.">Effect of electrical stimulation of the LES on LES pressure in a canine model.</a> American Journal of Physiology-Gastrointestinal and Liver Physiology. 295 (2), 389-394 (2008).</li><li>Rodr&#237;guez, L., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Electrical+stimulation+therapy+of+the+lower+esophageal+sphincter+is+successful+in+treating+GERD:+final+results+of+open-label+prospective+trial.">Electrical stimulation therapy of the lower esophageal sphincter is successful in treating GERD: final results of open-label prospective trial.</a> Surgical Endoscopy. 27 (4), 1083-1092 (2013).</li><li>Rinsma, N. F., Bouvy, N. D., Masclee, A. A. M., Conchillo, J. M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Electrical+stimulation+therapy+for+gastroesophageal+reflux+disease.">Electrical stimulation therapy for gastroesophageal reflux disease.</a> Journal of Neurogastroenterology and Motility. 20 (3), 287-293 (2014).</li><li>Rodr&#237;guez, L., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Two-year+results+of+intermittent+electrical+stimulation+of+the+lower+esophageal+sphincter+treatment+of+gastroesophageal+reflux+disease.">Two-year results of intermittent electrical stimulation of the lower esophageal sphincter treatment of gastroesophageal reflux disease.</a> Surgery. 157 (3), 556-567 (2015).</li><li>Kwiatek, M. A., Pandolfino, J. E. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=The+BravoTM+pH+capsule+system.">The BravoTM pH capsule system.</a> Digestive and Liver Disease. 40 (3), 156-160 (2008).</li><li>Karamanolis, G., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Bravo+48-hour+wireless+pH+monitoring+in+patients+with+non-cardiac+chest+pain.+objective+gastroesophageal+reflux+disease+parameters+predict+the+responses+to+proton+pump+inhibitors.">Bravo 48-hour wireless pH monitoring in patients with non-cardiac chest pain. objective gastroesophageal reflux disease parameters predict the responses to proton pump inhibitors.</a> Journal of Neurogastroenterology and Motility. 18 (2), 169-173 (2012).</li><li>Rodr&#237;guez, L., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Two-year+results+of+intermittent+electrical+stimulation+of+the+lower+esophageal+sphincter+treatment+of+gastroesophageal+reflux+disease.">Two-year results of intermittent electrical stimulation of the lower esophageal sphincter treatment of gastroesophageal reflux disease.</a> Surgery (United States). 157 (3), 556-567 (2015).</li><li>Hajer, J., Nov&#225;k, M., Rosina, J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Wirelessly+powered+endoscopically+implantable+devices+into+the+submucosa+as+the+possible+treatment+of+gastroesophageal+reflux+disease.">Wirelessly powered endoscopically implantable devices into the submucosa as the possible treatment of gastroesophageal reflux disease.</a> Gastroenterology Research and Practice. 2019, 1-7 (2019).</li><li>Deb, S., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Development+of+innovative+techniques+for+the+endoscopic+implantation+and+securing+of+a+novel,+wireless,+miniature+gastrostimulator+(with+videos).">Development of innovative techniques for the endoscopic implantation and securing of a novel, wireless, miniature gastrostimulator (with videos).</a> Gastrointestinal Endoscopy. 76 (1), 179-184 (2012).</li><li>Shin, P., Mikolajick, T., Ryssel, H. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=pH+Sensing+Properties+of+ISFETs+with+LPCVD+Silicon+Nitride+Sensitive-Gate.">pH Sensing Properties of ISFETs with LPCVD Silicon Nitride Sensitive-Gate.</a> The Journal of Electrical Engineering and Information Science. 2, 82-87 (1997).</li><li>Benhamou, P. -. Y., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Closed-loop+insulin+delivery+in+adults+with+type+1+diabetes+in+real-life+conditions:+a+12-week+multicentre,+open-label+randomised+controlled+crossover+trial.">Closed-loop insulin delivery in adults with type 1 diabetes in real-life conditions: a 12-week multicentre, open-label randomised controlled crossover trial.</a> The Lancet Digital Health. 1 (1), 17-25 (2019).</li><li>Nikolic, M., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Tailored+modern+GERD+therapy+-+steps+towards+the+development+of+an+aid+to+guide+personalized+anti-reflux+surgery.">Tailored modern GERD therapy - steps towards the development of an aid to guide personalized anti-reflux surgery.</a> Scientific Reports. 9 (1), 19174 (2019).</li><li>Hajer, J., Nov&#225;k, M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Autonomous+and+rechargeable+microneurostimulator+endoscopically+implantable+into+the+submucosa.">Autonomous and rechargeable microneurostimulator endoscopically implantable into the submucosa.</a> Journal of Visualized Experiments: JoVE. (139), e57268 (2018).</li><li>Pavelka, M., Roth, J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Parietal+Cells+Of+Stomach:+Secretion+Of+Acid.">Parietal Cells Of Stomach: Secretion Of Acid.</a> Functional Ultrastructure. , 202-203 (2010).</li><li>Jones, R. D., Neuman, M. R., Sanders, G., Cross, F. S. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Miniature+antimony+pH+electrodes+for+measuring+gastroesophageal+reflux.">Miniature antimony pH electrodes for measuring gastroesophageal reflux.</a> The Annals of Thoracic Surgery. 33 (5), 491-495 (1982).</li><li>Waugh, R. W., Buted, R. R. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=The+zero+bias+schottky+diode+detector+at+temperature+extremes-problems+and+solutions.">The zero bias schottky diode detector at temperature extremes-problems and solutions.</a> Proceedings of the WIRELESS Symposium. , 175-183 (1996).</li><li>Soffer, E. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Effect+of+electrical+stimulation+of+the+lower+esophageal+sphincter+in+gastroesophageal+reflux+disease+patients+refractory+to+proton+pump+inhibitors.">Effect of electrical stimulation of the lower esophageal sphincter in gastroesophageal reflux disease patients refractory to proton pump inhibitors.</a> World Journal of Gastrointestinal Pharmacology and Therapeutics. 7 (1), 145 (2016).</li><li>. Microsemi ZL70323 MICS-band RF miniaturized standard implant module (MiniSIM) Available from: <a target="_blank" href="https://www.microsemi.com/document-portal/doc_download/135307-zl70323-datasheet">https://www.microsemi.com/document-portal/doc_download/135307-zl70323-datasheet</a> (2015)</li></ol>

The authors have nothing to declare.

This method is suitable for researchers who work on the development of novel active implantable medical devices. It requires a level of proficiency in the manufacturing of electronic prototypes with surface mount components. The critical steps in the protocol are related to the manufacturing of the electronics, especially populating the PCBs, which is prone to operator error in placement and soldering of small components. Then, correct encapsulation is crucial to prolong the lifetime of the device when exposed to moistur...

The Montreal Consensus defines gastroesophageal reflux disease (GERD) as &#34;a condition that develops when refluxing the contents of the stomach causes unpleasant symptoms and/or complications&#34;. It may be associated with other specific complications such as esophageal strictures, Barrett&#39;s esophagus, or esophageal adenocarcinoma. GERD affects approximately 20% of the adult population, mainly in countries with high economic status1.
Ambulatory pH monitoring of pathological reflux (acid exposure time of more than 6%) allows us to distinguish the relationship between symptoms and acidic or non-acidic gastroesophageal reflux2,3. In patients unresponsive to PPI (proton pump inhibitor) therapy, pH monitoring can answer whether it is pathological gastroesophageal reflux and why the patient does not respond to standard PPI therapy. Various pH and impedance monitoring options are currently offered. One of the newer possibilities is wireless monitoring using implantable devices4,5.
GERD is associated with lower esophageal sphincter (LES) disorder, where the contractions shown during esophageal manometry are not pathological but have a reduced amplitude in long-term GERD. LES consists of smooth muscle and maintains tonic contractions due to myogenic and neurogenic factors. It relaxes due to vagal-mediated inhibition involving nitric oxide as a neurotransmitter6.
Electrical stimulation with two pairs of electrodes was proven to increase the contraction time of the LES in a canine reflux model7. The relaxation of the LES including the residual pressure during swallowing was not affected by both low and high frequency stimulation. High-frequency stimulation is an obvious choice because it requires less power and extends the battery life.
Although electrostimulation treatment (ET) of the lower esophageal sphincter is a relatively new concept in the treatment of patients with GERD, this therapy was shown to be safe and effective. This form of treatment has been shown to provide significant and lasting relief from the symptoms of GERD while eliminating the need for PPI treatment and reducing esophageal acid exposure8,9,10.
The current state-of-the-art pH sensor for diagnostics of GERD is the Bravo device11,12. At an estimated volume of 1.7 cm3, it can be implanted directly into the esophagus with or without visual endoscopic feedback and provides 24 h+ monitoring of pH in the esophagus.
Considering that electrostimulation therapy is one of the most promising alternatives for treating GERD not responding to standard therapy8,13, it makes sense to provide the data from the pH sensor to the neurostimulator. The recent research shows a clear path to future development in this field which will lead to rigid all-in-one implantable devices which will reside at the site of neurostimulation14,15. For this purpose, the ISFET (ion-sensitive field-effect transistor) is one of the best types of sensors because of its miniature nature, the possibility of on-chip integration of a reference electrode (gold in this case), and sufficiently high sensitivity. On silicon, the ISFET resembles the structure of a standard MOSFET (Metal Oxide Semiconductor Field Effect Transistor). However, the gate, normally connected to an electrical terminal, is replaced by a layer of active material in direct contact with the surrounding environment. In the case of pH-sensitive ISFETs, this layer is formed by silicon nitride (Si3N4)16.
The main disadvantage of endoscopically implantable devices is the inherent limitation of the battery size, which may lead to a reduced lifetime of these devices or motivate the manufacturers to develop advanced algorithms that will deliver the required effect at a lower energy cost. One of the examples of such an algorithm would be a closed-loop system for on-demand neurostimulation therapy of GERD. Similar to continuous glucose meters (CGM) + insulin pump systems17, such a system would employ an esophageal pH sensor or another sensor to detect the current pressure of the lower esophageal sphincter together with a neurostimulation unit.
The response to the neurostimulation therapy and the requirements for neurostimulation patterns can be individual13. Thus, it is important to develop independent sensors that could be used either for diagnosis and characterization of the dysfunction or to actively participate in calibrating the neurostimulation system according to the individual requirements of the patients18. These sensors should be as small as possible to not affect the normal functionality of the organ.
This manuscript describes a method of design and fabrication of an ISFET based pH sensor with amplitude-shift keying (ASK) transmitter and a small footprint passive rectenna-based receiver. Based on the simple architecture of the solution, the pH data can be received by an external receiver or even the implantable neurostimulator without any significant volume or power penalty. The ASK modulation is chosen because of the nature of the passive receiver, which is only capable of detection of received RF signal power (often called &#34;received signal strength&#34;). The schematic diagram, which is embedded as Supplementary material, shows the construction of the device. It is powered directly from two AG1 alkaline batteries, which provide a voltage between 2.0-3.0 V (based on the state of charge). The batteries power the internal microcontroller, which utilizes its ADC (analog-to-digital converter), DAC (digital-to-analog converter), internal operation amplifier, and FVR (fixed-voltage reference) peripherals to bias the ISFET pH sensor. The resulting &#34;gate&#34; voltage (the gold reference electrode) is proportional to the pH of the surrounding environment. A stable Ids current is provided by a low-side R2 sensing resistor. The source of the ISFET sensor is connected to the non-inverting input of the operational amplifier, while the inverting input is connected to the output voltage of the DAC module set to 960 mV. The output of the operational amplifier is connected to the drain pin of the ISFET. This operational amplifier regulates the drain voltage so that the voltage difference on the R2 resistor is always 960 mV; thus, a constant bias current of 29 &#181;A flows through the ISFET (when in normal operation). The gate voltage is then measured with an ADC. The microcontroller then powers on the RF transmitter via one of the GPIO (general purpose input/output) pins and transmits the sequence. The RF transmitter circuit involves a crystal and matching network which matches the output to 50 &#937; impedance.
For the experiments demonstrated here, we used a pig stomach with a long section of the esophagus mounted in a standardized plastic model. This is a commonly used model for practicing endoscopic techniques such as ESD (endoscopic submucosal dissection), POEM (oral endoscopic myotomy), endoscopic mucosal resection (EMR), hemostasis, etc. Concerning the closest possible anatomical parameters approaching human organs, we used the stomach and esophagus of pigs weighing 40-50 kg.

<table border="1" fo:keep-together.within-page="1" fo:keep-with-next.within-page="always">
	<tbody>
		<tr>
			<td>AG1 battery</td>
			<td>Panasonic</td>
			<td>SR621SW</td>
			<td>Two batteries per one implant</td>
		</tr>
		<tr>
			<td>Battery holder</td>
			<td>MYOUNG</td>
			<td>MY-521-01</td>
			<td></td>
		</tr>
		<tr>
			<td>Copper enamel wire for the antenna</td>
			<td>pro-POWER</td>
			<td>QSE Wire - 0.15 mm diameter, 38 SWG</td>
			<td></td>
		</tr>
		<tr>
			<td>Epoxy for encapsulation</td>
			<td>Loctite</td>
			<td>EA M-31 CL</td>
			<td>Two-part medical-grade ISO10993 compliant epoxy</td>
		</tr>
		<tr>
			<td>FEP cable for pH sensor</td>
			<td>Molex / Temp-Flex</td>
			<td>100057-0273</td>
			<td></td>
		</tr>
		<tr>
			<td>Flux cleaner</td>
			<td>Shesto</td>
			<td>UTFLLU05</td>
			<td>Prepare 5% solution in deionized water for cleaning by sonication</td>
		</tr>
		<tr>
			<td>Hemostatic clip</td>
			<td>Boston Scientific</td>
			<td>Resolution</td>
			<td></td>
		</tr>
		<tr>
			<td>Hot air gun + soldering iron</td>
			<td>W.E.P.</td>
			<td>Model 706</td>
			<td>Any soldering iron capable of soldering with tin and hot-air gun capable of maintaining 260 &#176;C can be used</td>
		</tr>
		<tr>
			<td>Impedance matching software</td>
			<td>Iowa Hills Software</td>
			<td>Smith Chart</td>
			<td>Can be downloaded from http://www.iowahills.com/9SmithChartPage.html - alternatively, any RF design software supports calculation of impedance matching components</td>
		</tr>
		<tr>
			<td>ISFET pH sensor on a PCB</td>
			<td>WinSense</td>
			<td>WIPS</td>
			<td>Order a model pre-mounted on a PCB with on-chip gold reference electrode</td>
		</tr>
		<tr>
			<td>Laboratory pH meter</td>
			<td>Hanna Instruments</td>
			<td>HI2210-02</td>
			<td>Used with HI1131B glass probe</td>
		</tr>
		<tr>
			<td>Microcontorller programmer</td>
			<td>Microchip</td>
			<td>PICkit 3</td>
			<td>Other PIC16 compatible programmers can be also used</td>
		</tr>
		<tr>
			<td>Pig stomach with esophagus</td>
			<td>Local pig farm</td>
			<td>Obtained from approx. 40&#8211;50 kg pig</td>
			<td>It is important that the stomach includes a full length of the esophagus.</td>
		</tr>
		<tr>
			<td>Printed circuit board - receiver</td>
			<td>Choose preferred PCB supplier</td>
			<td>According to pcb2.zip data</td>
			<td>One layer, 0.8 mm thickness, FR4, no mask</td>
		</tr>
		<tr>
			<td>Printed circuit board - sensor</td>
			<td>Choose preferred PCB supplier</td>
			<td>According to pcb1.zip data</td>
			<td>Two-layer with PTH, 0.6 mm thickness, FR4, 2x mask</td>
		</tr>
		<tr>
			<td>Receiver - 0R</td>
			<td>Vishay</td>
			<td>CRCW04020000Z0EDC</td>
			<td>See Figure 12 and Figure 13 for placement</td>
		</tr>
		<tr>
			<td>Receiver - 1.5 pF</td>
			<td>Murata</td>
			<td>GRM0225C1C1R5CA03L</td>
			<td>See Figure 12 and Figure 13 for placement</td>
		</tr>
		<tr>
			<td>Receiver - 100 pF</td>
			<td>Murata</td>
			<td>GRM0225C1E101JA02L</td>
			<td>See Figure 12 and Figure 13 for placement</td>
		</tr>
		<tr>
			<td>Receiver - 33 nH</td>
			<td>Pulse Electronics</td>
			<td>PE-0402CL330JTT</td>
			<td>See Figure 12 and Figure13 for placement</td>
		</tr>
		<tr>
			<td>Receiver - RF schottky diodes</td>
			<td>MACOM</td>
			<td>MA4E2200B1-287T</td>
			<td>See Figure 12 and Figure 13 for placement</td>
		</tr>
		<tr>
			<td>Receiver - SMA antenna</td>
			<td>LPRS</td>
			<td>ANT-433MS</td>
			<td></td>
		</tr>
		<tr>
			<td>Receiver - SMA connector</td>
			<td>Linx Technologies</td>
			<td>CONSMA001</td>
			<td>See Figure 12 and Figure 13 for placement</td>
		</tr>
		<tr>
			<td>Sensor - C1</td>
			<td>Murata</td>
			<td>GRM0225C1H8R0DA03L</td>
			<td>8 pF 0402 capacitor</td>
		</tr>
		<tr>
			<td>Sensor - C2</td>
			<td>Murata</td>
			<td>GRM0225C1H8R0DA03L</td>
			<td>8 pF 0402 capacitor</td>
		</tr>
		<tr>
			<td>Sensor - C3</td>
			<td>Murata</td>
			<td>GCM155R71H102KA37D</td>
			<td>1 nF 0402 capacitor</td>
		</tr>
		<tr>
			<td>Sensor - C4</td>
			<td>Murata</td>
			<td>GRM0225C1H1R8BA03L</td>
			<td>1.8 pF</td>
		</tr>
		<tr>
			<td>Sensor - C5</td>
			<td>Vishay</td>
			<td>CRCW04020000Z0EDC</td>
			<td>Place 0R 0402 resistor or use to match the antenna</td>
		</tr>
		<tr>
			<td>Sensor - C6</td>
			<td>Murata</td>
			<td>GRM155C81C105KE11J</td>
			<td>1 uF 0402 capacitor</td>
		</tr>
		<tr>
			<td>Sensor - C7</td>
			<td>Murata</td>
			<td>GRM155C81C105KE11J</td>
			<td>1 uF 0402 capacitor</td>
		</tr>
		<tr>
			<td>Sensor - C8</td>
			<td>Murata</td>
			<td>GRM022R61A104ME01L</td>
			<td>100 nF 0402 capacitor</td>
		</tr>
		<tr>
			<td>Sensor - IC1</td>
			<td>Microchip</td>
			<td>MICRF113YM6-TR</td>
			<td>MICRF113 RF transmitter</td>
		</tr>
		<tr>
			<td>Sensor - IC2</td>
			<td>Microchip</td>
			<td>PIC16LF1704-I/ML</td>
			<td>PIC16LF1704 low-power microcontroller</td>
		</tr>
		<tr>
			<td>Sensor - R1</td>
			<td>Vishay</td>
			<td>CRCW040210K0FKEDC</td>
			<td>10 kOhm 0402 resistor</td>
		</tr>
		<tr>
			<td>Sensor - R2</td>
			<td>Vishay</td>
			<td>CRCW040233K0FKEDC</td>
			<td>33 kOhm 0402 resistor</td>
		</tr>
		<tr>
			<td>Sensor - R3</td>
			<td>Vishay</td>
			<td>CRCW04021K00FKEDC</td>
			<td>1 kOhm 0402 resistor</td>
		</tr>
		<tr>
			<td>Sensor - R5</td>
			<td>Vishay</td>
			<td>CRCW040210K0FKEDC</td>
			<td>10 kOhm 0402 resistor</td>
		</tr>
		<tr>
			<td>Sensor - X1</td>
			<td>ABRACON</td>
			<td>ABM8W-13.4916MHZ-8-J2Z-T3</td>
			<td>3.2 x 2.5 mm 13.4916 MHz 8 pF crystal</td>
		</tr>
		<tr>
			<td>Titanium wire</td>
			<td>Sigma-Aldrich</td>
			<td>GF36846434</td>
			<td>0.125 mm titanium wire</td>
		</tr>
		<tr>
			<td>Vector network analyzer</td>
			<td>mini RADIO SOLUTIONS</td>
			<td>miniVNA Tiny</td>
			<td>Other vector network analyzers can be used - the required operation frequency is 300&#8211;500 MHz, resolution bandwidth equal or lower than 1 MHz, output power of no more than 0 dBm and dynamic range preferably better than 60 dB for the receiving front-end</td>
		</tr>
	</tbody>
</table>

construction of a wireless-enabled endoscopically implantable sensor for ph monitoring with zero-bias schottky diode-based receiver

Ambulatory pH monitoring of pathological reflux is an opportunity to observe the relationship between symptoms and exposure of the esophagus to acidic or non-acidic refluxate. This paper describes a method for the development, manufacturing, and implantation of a miniature wireless-enabled pH sensor. The sensor is designed to be implanted endoscopically with a single hemostatic clip. A fully passive rectenna-based receiver based on a zero-bias Schottky diode is also constructed and tested. To construct the device, a two-layer printed circuit board and off-the-shelf components were used. A miniature microcontroller with integrated analog peripherals is used as an analog front end for the ion-sensitive field-effect transistor (ISFET) sensor and to generate a digital signal which is transmitted with an amplitude shift keying transmitter chip. The device is powered by two primary alkaline cells. The implantable device has a total volume of 0.6 cm3 and a weight of 1.2 grams, and its performance was verified in an ex vivo model (porcine esophagus and stomach). Next, a small footprint passive rectenna-based receiver which can be easily integrated either into an external receiver or the implantable neurostimulator, was constructed and proven to receive the RF signal from the implant when in proximity (20 cm) to it. The small size of the sensor provides continuous pH monitoring with minimal obstruction of the esophagus. The sensor could be used in routine clinical practice for 24/96 h esophageal pH monitoring without the need to insert a nasal catheter. The &#34;zero-power&#34; nature of the receiver also enables the use of the sensor for automatic in-vivo calibration of miniature lower esophageal sphincter neurostimulation devices. An active sensor-based control enables the development of advanced algorithms to minimize the used energy to achieve a desirable clinical outcome. One of the examples of such an algorithm would be a closed-loop system for on-demand neurostimulation therapy of gastroesophageal reflux disease (GERD).

A device capable of autonomous pH sensing and wireless transmitting of the pH value was successfully constructed, as shown in Figure 8. The constructed device is a miniature model; it weighs 1.2 g and has a volume of 0.6 cm3. The approximate dimensions are 18 mm x 8.5 mm x 4.5 mm. As shown in Figure&#160;15, Figure&#160;16, and Figure&#160;17, it can be implanted to the proxi...

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Construction of a Wireless-Enabled Endoscopically Implantable Sensor for pH Monitoring with Zero-Bias Schottky Diode-based Receiver

The manuscript presents a miniature implantable pH sensor with ASK modulated wireless output together with a fully passive receiver circuit based on zero-bias Schottky diodes. This solution can be used as a basis in the development of in vivo calibrated electrostimulation therapy devices and for ambulatory pH monitoring.

Ambulatory pH monitoring of pathological reflux is an opportunity to observe the relationship between symptoms and exposure of the esophagus to acidic or ...

The protocol shows the fabrication of wireless implantable pH sensor that transmit data to a fully passive receiver, enabling very power efficient delivery of data from one implantable device to another. The sensor can be manufactured by hand and by commonly available techniques. Next, the method of data transmission can be directly reused in the development of different implantable devices.It is critical to thoroughly inspect the wireless pH sensor after every step. The components used for its fabrication are very small and short circuits or misplacement during the fabrication can occur. To begin with, place the ISFET pH sensor mounted on a PCB on a flat surface and solder a 15 millimeter section of fluorinated ethylene propylene-coated cable to the solderable electrodes of the pH sensor without contaminating dye and PCB with flux.Mix a minimum of two milliliters of two-part epoxy to encapsulate the soldered electrodes and then use black opaque epoxy for later inspection. Observe the easy visibility of sensor parts exposed to the environment without opaque epoxy. Transfer the mixed epoxy to a one milliliter syringe with a 0.5 millimeter flat-end needle and coat the soldering area of pH sensors with epoxy, ensuring coating of the whole area of PCB electrodes and the exposed wire.Inspect the coated area under a microscope for any uncoated exposed metal parts. After repeating the coating process of uncoated metal, trim the wires to the length and angle, then coat the ends with solder to avoid fraying. After placing PCB with components in a side up position, apply solder paste to all the exposed gold-plated pads.Next, place passive and active components using tweezers. After soldering and cooling to room temperature, inspect the PCB under the microscope to verify the placement of the components and shorts. Program firmware to the micro controller and set up the programming software as described in the text.Next, set the programmer to power the device with a voltage of approximately 2.5 volts. Then de-solder the five wires after programming. Solder two battery holders to the opposite part of the PCB.Next, solder the pH sensor assembly to the terminals of the PCB, then insert two AG1 batteries into the battery holders. After preparing epoxy, encapsulate the device with the epoxy as previously described. Let the epoxy cure at room temperature.Attach the wire hook to the device with a drop of fast curing epoxy. After curing at room temperature, pH sensor could be located on the bottom left side of the implantable device. Solder the components using the soldering gun.To manufacture the rectenna receiver again or proceed without receiver matching, use the values of the components provided here and skip the recording of S11 Smith chart in the next step. Otherwise, solder the SMA connector to the PCB. Attach a vector network analyzer input to the SMA connector.Record the S11 Smith chart of the rectenna. Observe the response and record the impedance. Use an impedance matching calculator software to determine the values of matching components.Solder the impedance matching components and inspect under a microscope for short circuits and component placement. After measuring with spectrum analyzer again, confirm that the voltage standing wave ratio is under three between 300 to 500 megahertz. Otherwise, repeat with different matching components.After the device is activated post 24 hour of the battery's insertion, inspect the sensor's output by observing the signal shown in the oscilloscope. Prepare 2%hydrochloric acid solution and 100 millimolar buffer solution of pH four, pH seven, and pH 10. Submerge the capsule in every beaker and record at least three samples.Measure the period between the second and third pulse. And after filling it in the provided spreadsheet, determine the calibration coefficients for the pH sensor using the spreadsheet. After preparing an ex vivo endoscopic porcine model of the stomach and a long segment of the esophagus, grasp the sensor externally with a hemostatic clip.Insert the endoscope with the sensor in the clip in the standard way into the model. After placing the clip with the sensor close to the lower esophageal sphincter, rotate the endoscope against the esophageal wall, open the clip and then push towards the esophageal wall. Close and release the clip.While the sensor remains attached to the esophageal wall at the desired location, extract the endoscope. Place the receiver within 10 centimeters of the implanted sensor. Inject 50 milliliters of the solutions with various pH values into the esophagus and observe the changes in the sensor's response.Retract the endoscope after every injection and read the value no earlier than 30 seconds after injection and use the spreadsheet to calculate the pH measured by the sensor. Wash the esophagus with 100 milliliters of deionized water between injecting solutions with different pH. When the passive rectenna receiver was put into proximity of the pH sensing device, clear voltage spikes were observed when the device was transmitting.The first two short pulses were synchronization pulses. The time between second and third pulse linearly translates to the pH of the environment that the sensor was subjected to. Based on a simple two-point calibration with the buffers of pH four and pH 10, the sensor returned stable and repeatable pH value readings.The mean and standard deviation of errors were 0.25 and 0.30 when tested in solutions and beakers and were 0.31 and 0.36 in an ex vivo model. The effect of a mobile phone antenna with an active GSM call had only a minor negative effect on receiving the data from the sensor as demonstrated for 20 centimeters, 10 centimeters, and five centimeters distance between the edge of the phone and the receiver. The encapsulation of the sensor must be done and inspected properly to prolong the lifetime of the device when implanted.Next, correct placement of the hemostatic clip is critical. This research paves the way for the development of wireless networks of implantable devices by creating an energy efficient way to transfer data especially from the receiver point of view.

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Research

JoVE Journal

Bioengineering

2.4K visualizações.  Charles University. O protocolo mostra a fabricação de sensor de pH implantável sem fio que transmite dados para um receptor totalmente passivo, permitindo a entrega muito eficiente de dados de um dispositivo implantável para outro. O sensor pode ser fabricado à mão e por técnicas comumente disponíveis. Em seguida, o método de transmissão de dados pode ser reutilizado diretamente no desenvolvimento de diferentes dispositivos implantáveis.É fundamental inspecionar completamente o sensor de pH s...