Name: construction of a wireless-enabled endoscopically implantable sensor for ph monitoring with zero-bias schottky diode-based receiver
Uploaded: 2021-08-27T13:30:00
Description: Watch this Scientific Journal Video about Construction of a Wireless-Enabled Endoscopically Implantable Sensor for pH Monitoring with Zero-Bias Schottky Diode-based Receiver at JoVE.com

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. -. 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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>

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...

Watch this Scientific Journal Video about Construction of a Wireless-Enabled Endoscopically Implantable Sensor for pH Monitoring with Zero-Bias Schottky Diode-based Receiver at JoVE.com

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

Biomolecular Detection employing the Interferometric Reflectance Imaging Sensor (IRIS)

The sensitive measurement of biomolecular interactions has use in many fields and industries such as basic biology and microbiology, environmental/agricultural/biodefense monitoring, nanobiotechnology, and more. For diagnostic applications, monitoring (detecting) the presence, absence, or abnormal expression of targeted proteomic or genomic biomarkers found in patient samples can be used to determine treatment approaches or therapy efficacy. In the research arena, information on molecular affinities and specificities are useful for fully characterizing the systems under investigation.
Many of the current systems employed to determine molecular concentrations or affinities rely on the use of labels. Examples of these systems include immunoassays such as the enzyme-linked immunosorbent assay (ELISA), polymerase chain reaction (PCR) techniques, gel electrophoresis assays, and mass spectrometry (MS). Generally, these labels are fluorescent, radiological, or colorimetric in nature and are directly or indirectly attached to the molecular target of interest. Though the use of labels is widely accepted and has some benefits, there are drawbacks which are stimulating the development of new label-free methods for measuring these interactions. These drawbacks include practical facets such as increased assay cost, reagent lifespan and usability, storage and safety concerns, wasted time and effort in labelling, and variability among the different reagents due to the labelling processes or labels themselves. On a scientific research basis, the use of these labels can also introduce difficulties such as concerns with effects on protein functionality/structure due to the presence of the attached labels and the inability to directly measure the interactions in real time.
Presented here is the use of a new label-free optical biosensor that is amenable to microarray studies, termed the Interferometric Reflectance Imaging Sensor (IRIS), for detecting proteins, DNA, antigenic material, whole pathogens (virions) and other biological material. The IRIS system has been demonstrated to have high sensitivity, precision, and reproducibility for different biomolecular interactions [1-3]. Benefits include multiplex imaging capacity, real time and endpoint measurement capabilities, and other high-throughput attributes such as reduced reagent consumption and a reduction in assay times. Additionally, the IRIS platform is simple to use, requires inexpensive equipment, and utilizes silicon-based solid phase assay components making it compatible with many contemporary surface chemistry approaches.
Here, we present the use of the IRIS system from preparation of probe arrays to incubation and measurement of target binding to analysis of the results in an endpoint format. The model system will be the capture of target antibodies which are specific for human serum albumin (HSA) on HSA-spotted substrates.

Biomolecular Detection employing the Interferometric Reflectance Imaging Sensor IRIS

Quantitative, high-throughput, real-time, and label-free biomolecular detection (DNA, protein, etc.) on SiO2 surfaces can be achieved using a simple interferometric technique which relies on LED illumination, minimal optical components, and a camera. The Interferometric Reflectance Imaging Sensor (IRIS) is inexpensive, simple to use, and amenable to microarray formats.

The sensitive measurement of biomolecular interactions has use in many fields and industries such as basic biology and microbiology, ...

Monitoring Protein Adsorption with Solid-state Nanopores

Solid-state nanopores have been used to perform measurements at the single-molecule level to examine the local structure and flexibility of nucleic acids 1-6, the unfolding of proteins 7, and binding affinity of different ligands 8. By coupling these nanopores to the resistive-pulse technique 9-12, such measurements can be done under a wide variety of conditions and without the need for labeling 3. In the resistive-pulse technique, an ionic salt solution is introduced on both sides of the nanopore. Therefore, ions are driven from one side of the chamber to the other by an applied transmembrane potential, resulting in a steady current. The partitioning of an analyte into the nanopore causes a well-defined deflection in this current, which can be analyzed to extract single-molecule information. Using this technique, the adsorption of single proteins to the nanopore walls can be monitored under a wide range of conditions 13. Protein adsorption is growing in importance, because as microfluidic devices shrink in size, the interaction of these systems with single proteins becomes a concern. This protocol describes a rapid assay for protein binding to nitride films, which can readily be extended to other thin films amenable to nanopore drilling, or to functionalized nitride surfaces. A variety of proteins may be explored under a wide range of solutions and denaturing conditions. Additionally, this protocol may be used to explore more basic problems using nanopore spectroscopy.

A method of using solid-state nanopores to monitor the non-specific adsorption of proteins onto an inorganic surface is described. The method employs the resistive-pulse principle, allowing for the adsorption to be probed in real-time and at the single-molecule level. Because the process of single protein adsorption is far from equilibrium, we propose the employment of parallel arrays of synthetic nanopores, enabling for the quantitative determination of the apparent first-order reaction rate constant of protein adsorption as well as and the Langmuir adsorption constant.

Solid-state nanopores have been used to perform measurements at the single-molecule level to examine the local structure and flexibility of nucleic acids ...

Hollow Microneedle-based Sensor for Multiplexed Transdermal Electrochemical Sensing

The development of a minimally invasive multiplexed monitoring system for rapid analysis of biologically-relevant molecules could offer individuals suffering from chronic medical conditions facile assessment of their immediate physiological state. Furthermore, it could serve as a research tool for analysis of complex, multifactorial medical conditions. In order for such a multianalyte sensor to be realized, it must be minimally invasive, sampling of interstitial fluid must occur without pain or harm to the user, and analysis must be rapid as well as selective.
Initially developed for pain-free drug delivery, microneedles have been used to deliver vaccines and pharmacologic agents (e.g., insulin) through the skin.1-2 Since these devices access the interstitial space, microneedles that are integrated with microelectrodes can be used as transdermal electrochemical sensors. Selective detection of glucose, glutamate, lactate, hydrogen peroxide, and ascorbic acid has been demonstrated using integrated microneedle-electrode devices with carbon fibers, modified carbon pastes, and platinum-coated polymer microneedles serving as transducing elements.3-7,8
This microneedle sensor technology has enabled a novel and sophisticated analytical approach for in situ and simultaneous detection of multiple analytes. Multiplexing offers the possibility of monitoring complex microenvironments, which are otherwise difficult to characterize in a rapid and minimally invasive manner. For example, this technology could be utilized for simultaneous monitoring of extracellular levels of, glucose, lactate and pH,9 which are important metabolic indicators of disease states7,10-14 (e.g., cancer proliferation) and exercise-induced acidosis.15

This article details the construction of a multiplexed microneedle-based sensor. The device is being developed for in situ sampling and electrochemical analysis of multiple analytes in a rapid and selective manner. We envision clinical medicine and biomedical research uses for these microneedle-based sensors.

The development of a minimally invasive multiplexed monitoring system for rapid analysis of biologically-relevant molecules could offer individuals ...

Mass Cytometry: Protocol for Daily Tuning and Running Cell Samples on a CyTOF Mass Cytometer

In recent years, the rapid analysis of single cells has commonly been performed using flow cytometry and fluorescently-labeled antibodies. However, the issue of spectral overlap of fluorophore emissions has limited the number of simultaneous probes. In contrast, the new CyTOF mass cytometer by DVS Sciences couples a liquid single-cell introduction system to an ICP-MS.1 Rather than fluorophores, chelating polymers containing highly-enriched metal isotopes are coupled to antibodies or other specific probes.2-5 Because of the metal purity and mass resolution of the mass cytometer, there is no "spectral overlap" from neighboring isotopes, and therefore no need for compensation matrices. Additionally, due to the use of lanthanide metals, there is no biological background and therefore no equivalent of autofluorescence. With a mass window spanning atomic mass 103-203, theoretically up to 100 labels could be distinguished simultaneously. Currently, more than 35 channels are available using the chelating reagents available from DVS Sciences, allowing unprecedented dissection of the immunological profile of samples.6-7
Disadvantages to mass cytometry include the strict requirement for a separate metal isotope per probe (no equivalent of forward or side scatter), and the fact that it is a destructive technique (no possibility of sorting recovery). The current configuration of the mass cytometer also has a cell transmission rate of only ~25%, thus requiring a higher input number of cells.
Optimal daily performance of the mass cytometer requires several steps. The basic goal of the optimization is to maximize the measured signal intensity of the desired metal isotopes (M) while minimizing the formation of oxides (M+16) that will decrease the M signal intensity and interfere with any desired signal at M+16. The first step is to warm up the machine so a hot, stable ICP plasma has been established. Second, the settings for current and make-up gas flow rate must be optimized on a daily basis. During sample collection, the maximum cell event rate is limited by detector efficiency and processing speed to 1000 cells/sec. However, depending on the sample quality, a slower cell event rate (300-500 cells/sec) is usually desirable to allow better resolution between cells events and thus maximize intact singlets over doublets and debris. Finally, adequate cleaning of the machine at the end of the day helps minimize background signal due to free metal.

The steps necessary for daily tuning and optimization of the performance of a CyTOF mass cytometer are described. Comments on optimal sample preparation and flow rate are discussed

In recent years, the rapid analysis of single cells has commonly been performed using flow cytometry and fluorescently-labeled antibodies. However, the ...

Construction and Characterization of a Novel Vocal Fold Bioreactor

In vitro engineering of mechanically active tissues requires the presentation of physiologically relevant mechanical conditions to cultured cells. To emulate the dynamic environment of vocal folds, a novel vocal fold bioreactor capable of producing vibratory stimulations at fundamental phonation frequencies is constructed and characterized. The device is composed of a function generator, a power amplifier, a speaker selector and parallel vibration chambers. Individual vibration chambers are created by sandwiching a custom-made silicone membrane between a pair of acrylic blocks. The silicone membrane not only serves as the bottom of the chamber but also provides a mechanism for securing the cell-laden scaffold. Vibration signals, generated by a speaker mounted underneath the bottom acrylic block, are transmitted to the membrane aerodynamically by the oscillating air. Eight identical vibration modules, fixed on two stationary metal bars, are housed in an anti-humidity chamber for long-term operation in a cell culture incubator. The vibration characteristics of the vocal fold bioreactor are analyzed non-destructively using a Laser Doppler Vibrometer (LDV). The utility of the dynamic culture device is demonstrated by culturing cellular constructs in the presence of 200-Hz sinusoidal vibrations with a mid-membrane displacement of 40 &#181;m. Mesenchymal stem cells cultured in the bioreactor respond to the vibratory signals by altering the synthesis and degradation of vocal fold-relevant, extracellular matrix components. The novel bioreactor system presented herein offers an excellent in vitro platform for studying vibration-induced mechanotransduction and for the engineering of functional vocal fold tissues.

A novel vocal fold bioreactor capable of delivering physiologically relevant, vibratory stimulation to cultured cells is constructed and characterized. This dynamic culture device, when combined with a fibrous poly(&#949;-caprolactone) scaffold, creates a vocal fold-mimetic environment that modulates the behaviors of mesenchymal stem cells.

In vitro engineering of mechanically active tissues requires the presentation of physiologically relevant mechanical conditions to cultured cells. To ...

Biomembrane Fabrication by the Solvent-assisted Lipid Bilayer (SALB) Method

In order to mimic cell membranes, the supported lipid bilayer (SLB) is an attractive platform which enables in vitro investigation of membrane-related processes while conferring biocompatibility and biofunctionality to solid substrates. The spontaneous adsorption and rupture of phospholipid vesicles is the most commonly used method to form SLBs. However, under physiological conditions, vesicle fusion (VF) is limited to only a subset of lipid compositions and solid supports. Here, we describe a one-step general procedure called the solvent-assisted lipid bilayer (SALB) formation method in order to form SLBs which does not require vesicles. The SALB method involves the deposition of lipid molecules onto a solid surface in the presence of water-miscible organic solvents (e.g., isopropanol) and subsequent solvent-exchange with aqueous buffer solution in order to trigger SLB formation. The continuous solvent exchange step enables application of the method in a flow-through configuration suitable for monitoring bilayer formation and subsequent alterations using a wide range of surface-sensitive biosensors. The SALB method can be used to fabricate SLBs on a wide range of hydrophilic solid surfaces, including those which are intractable to vesicle fusion. In addition, it enables fabrication of SLBs composed of lipid compositions which cannot be prepared using the vesicle fusion method. Herein, we compare results obtained with the SALB and conventional vesicle fusion methods on two illustrative hydrophilic surfaces, silicon dioxide and gold. To optimize the experimental conditions for preparation of high quality bilayers prepared via the SALB method, the effect of various parameters, including the type of organic solvent in the deposition step, the rate of solvent exchange, and the lipid concentration is discussed along with troubleshooting tips. Formation of supported membranes containing high fractions of cholesterol is also demonstrated with the SALB method, highlighting the technical capabilities of the SALB technique for a wide range of membrane configurations.

Biomembrane Fabrication by the Solvent-assisted Lipid Bilayer SALB Method

We present an experimental protocol to form a supported lipid bilayer on solid substrates without using lipid vesicles. We demonstrate a one-step method to form a lipid bilayer on silicon dioxide and gold as well as supported membranes with cholesterol-enriched domain for various biological applications.

In order to mimic cell membranes, the supported lipid bilayer (SLB) is an attractive platform which enables in vitro investigation of membrane-related ...

Real Time Monitoring of Intracellular Bile Acid Dynamics Using a Genetically Encoded FRET-based Bile Acid Sensor

F&#246;rster Resonance Energy Transfer (FRET) has become a powerful tool for monitoring protein folding, interaction and localization in single cells. Biosensors relying on the principle of FRET have enabled real-time visualization of subcellular signaling events in live cells with high temporal and spatial resolution. Here, we describe the application of a genetically encoded Bile Acid Sensor (BAS) that consists of two fluorophores fused to the farnesoid X receptor ligand binding domain (FXR-LBD), thereby forming a bile acid sensor that can be activated by a large number of bile acids species and other (synthetic) FXR ligands. This sensor can be targeted to different cellular compartments including the nucleus (NucleoBAS) and cytosol (CytoBAS) to measure bile acid concentrations locally. It allows rapid and simple quantitation of cellular bile acid influx, efflux and subcellular distribution of endogenous bile acids without the need for labeling with fluorescent tags or radionuclei. Furthermore, the BAS FRET sensors can be useful for monitoring FXR ligand binding. Finally, we show that this FRET biosensor can be combined with imaging of other spectrally distinct fluorophores. This allows for combined analysis of intracellular bile acid dynamics and i) localization and/or abundance of proteins of interest, or ii) intracellular signaling in a single cell.

We provide a detailed protocol to study bile acid dynamics in living cells using a genetically encoded BAS FRET sensor. This Bile Acid Sensor represents a unique tool to study (regulation of) bile acid transport and FXR activation in a wide range of cell types.

F&#246;rster Resonance Energy Transfer (FRET) has become a powerful tool for monitoring protein folding, interaction and localization in single cells. ...

Extraction of Plant-based Capsules for Microencapsulation Applications

Microcapsules derived from plant-based spores or pollen provide a robust platform for a diverse range of microencapsulation applications. Sporopollenin exine capsules (SECs) are obtained when spores or pollen are processed so as to remove the internal sporoplasmic contents. The resulting hollow microcapsules exhibit a high degree of micromeritic uniformity and retain intricate microstructural features related to the particular plant species. Herein, we demonstrate a streamlined process for the production of SECs from Lycopodium clavatum spores and for the loading of hydrophilic compounds into these SECs. The current SEC isolation procedure has been recently optimized to significantly reduce the processing requirements which are conventionally used in SEC isolation, and to ensure the production of intact microcapsules. Natural L. clavatum spores are defatted with acetone, treated with phosphoric acid, and extensively washed to remove sporoplasmic contents. After acetone defatting, a single processing step using 85% phosphoric acid has been shown to remove all sporoplasmic contents. By limiting the acid processing time to 30 hr, it is possible to isolate clean SECs and avoid SEC fracturing, which has been shown to occur with prolonged processing time. Extensive washing with water, dilute acids, dilute bases, and solvents ensures that all sporoplasmic material and chemical residues are adequately removed. The vacuum loading technique is utilized to load a model protein (Bovine Serum Albumin) as a representative hydrophilic compound. Vacuum loading provides a simple technique to load various compounds without the need for harsh solvents or undesirable chemicals which are often required in other microencapsulation protocols. Based on these isolation and loading protocols, SECs provide a promising material for use in a diverse range of microencapsulation applications, such as, therapeutics, foods, cosmetics, and personal care products.

This protocol/manuscript describes a streamlined process for the production of sporopollenin exine capsules (SECs) from Lycopodium clavatum spores and for the loading of hydrophilic compounds into these SECs.

Microcapsules derived from plant-based spores or pollen provide a robust platform for a diverse range of microencapsulation applications. Sporopollenin ...

Construction and Setup of a Bench-scale Algal Photosynthetic Bioreactor with Temperature, Light, and pH Monitoring for Kinetic Growth Tests

The optimal design and operation of photosynthetic bioreactors (PBRs) for microalgal cultivation is essential for improving the environmental and economic performance of microalgae-based biofuel production. Models that estimate microalgal growth under different conditions can help to optimize PBR design and operation. To be effective, the growth parameters used in these models must be accurately determined. Algal growth experiments are often constrained by the dynamic nature of the culture environment, and control systems are needed to accurately determine the kinetic parameters. The first step in setting up a controlled batch experiment is live data acquisition and monitoring. This protocol outlines a process for the assembly and operation of a bench-scale photosynthetic bioreactor that can be used to conduct microalgal growth experiments. This protocol describes how to size and assemble a flat-plate, bench-scale PBR from acrylic. It also details how to configure a PBR with continuous pH, light, and temperature monitoring using a data acquisition and control unit, analog sensors, and open-source data acquisition software.

This paper describes the assembly process and operation of a bench-scale photosynthetic bioreactor that can be used, in conjunction with other methods, to estimate pertinent kinetic growth parameters. This system continuously monitors the pH, light, and temperature using sensors, a data acquisition and control unit, and open-source data acquisition software.

The optimal design and operation of photosynthetic bioreactors (PBRs) for microalgal cultivation is essential for improving the environmental and economic ...

Manufacturing of a Nafion-coated, Reduced Graphene Oxide/Polyaniline Chemiresistive Sensor to Monitor pH in Real-time During Microbial Fermentation

Here, we report the engineering of a solid-state micro pH sensor based on polyaniline-functionalized, electrochemically reduced graphene oxide (ERGO-PA). Electrochemically reduced graphene oxide acts as the conducting layer and polyaniline acts as a pH-sensitive layer. The pH-dependent conductivity of polyaniline occurs by doping of holes during protonation and by the dedoping of holes during deprotonation. We found that an ERGO-PA solid-state electrode was not functional as such in fermentation processes. The electrochemically active species that the bacteria produce during the fermentation process interfere with the electrode response. We successfully applied Nafion as a proton-conducting layer over ERGO-PA. The Nafion-coated electrodes (ERGO-PA-NA) show a good sensitivity of 1.71 &#937;/pH (pH 4 - 9) for chemiresistive sensor measurements. We tested the ERGO-PA-NA electrode in real-time in the fermentation of Lactococcus lactis. During the growth of L. lactis, the pH of the medium changed from pH 7.2 to pH 4.8 and the resistance of the ERGO-PA-NA solid-state electrode changed from 294.5 &#937; to 288.6 &#937; (5.9 &#937; per 2.4 pH unit). The pH response of the ERGO-PA-NA electrode compared with the response of a conventional glass-based pH electrode shows that reference-less solid-state microsensor arrays operate successfully in a microbiological fermentation.

Here, we report the protocol for the fabrication of a Nafion-coated, polyaniline-functionalized, electrochemically reduced graphene oxide chemiresistive micro pH sensor. This chemiresistor-based, solid-state micro pH sensor can detect pH changes in real-time during a Lactococcus lactis fermentation process.

Here, we report the engineering of a solid-state micro pH sensor based on polyaniline-functionalized, electrochemically reduced graphene oxide (ERGO-PA). ...