Grantee Research Project Results
Final Report: Low-cost colorimetric sensor for methane emission monitoring
EPA Contract Number: EPD17033Title: Low-cost colorimetric sensor for methane emission monitoring
Investigators: Fan, Benson
Small Business: Biolnspira, Inc.
EPA Contact: Richards, April
Phase: I
Project Period: September 1, 2017 through August 29, 2018
Project Amount: $100,000
RFA: Small Business Innovation Research (SBIR) - Phase I (2017) RFA Text | Recipients Lists
Research Category: Small Business Innovation Research (SBIR) , SBIR - Air and Climate
Description:
This Environmental Protection Agency Small Business Innovative Research Phase I project aims to develop small and low cost hand-held natural gas sensor for surveyors and leak inspection crews in utilities and oil and gas industries. Currently, on-site, timely and accurate identification of fugitive emissions relies on bulky and expensive instruments, thus limiting widespread use and adaptation of such technology. No technology today is able to fill the sweet spot to provide the sensitivity, cost, and portability that the gas industry is in dire need of. BioInspira has developed arrays of color thin film made from self-assembled M13 bacteriophages that has been genetically modified to bind to specific gas chemicals, and the thin film changes color depending on the types of gases and concentrations. BioInspira aims to address this challenge through using these color thin film arrays to sense different components of natural gas in order to provide an accurate, small, power-efficient, and low-cost natural gas sensor. During the Phase I project, the BioInspira team focused on the following objectives to achieve the ultimate goal:
- Construct accurate calibration systems to calibrate the sensor against various level of temp. & humidity
- Precisely control sensor production to ensure product consistency and minimize variation
- Optimize sensor material production parameters and improve sensor yield
- Miniaturize sensor mechanical design to reduce cost, weight, while improving performance
Summary/Accomplishments (Outputs/Outcomes):
1.Sensor Calibration System
Initially proposed in the technical content, the team anticipated using a mini Coriolis Flow liquid mass flow controller, a controlled evaporator mixer, as well as two mass flow controllers to set up the calibration system. The team envisioned that a micro pump will push pressurized pure water through the liquid mass flow controller and into the controlled vaporizer. Once inside the vaporizer, the water will completely vaporize and be carried away by the carrier gas to be introduced to the sensor in the flow cell. However, after verification, the team has found that the setup was not able to maintain stable levels of humidity. Due to this reason, the team changed to using a dew point generator to maintain constant humidity level, as well as using a temperature chamber to maintain the temperature of the sensor chamber. After confirming system stability, the team move forward with sensor calibration.
A reference humidity sensor is included in our sensor device to compensate for the changes in humidity. The on-board humidity sensor has a 0.1% relative humidity (RH) resolution, and a 0.01C temperature resolution. With this resolution, it is believed that the on-board sensors are enough as a reference. However, it was found through calibration that the metal oxide semiconductor-based (MOS-based) humidity sensor response time is too slow, as shown in Figure 1 Left. This is a problem because the phage sensor's response time is less than 10 seconds, and having a humidity reference response time that is different from the phage sensor's response time will create overcompensation effect (the data compensation will kick in after the initial change in humidity). To address the problem, we have engineered two humidity-specific phage sensors were made, labeled "Phage" and "Phage Sensor 2". Both humidity phages have been calibrated from 5% to 90% humidity level at 1% increments. In testing the humidity phage sensors, it was found that the response time is now around 10 seconds. This makes the humidity phage sensor a more preferable reference than the MOS humidity sensor. It is anticipated that if the humidity phages have good cross-sensitivity responses (such as it does not react to common gases such as carbon dioxide), the humidity phages will be replacing the current on-board humidity sensors for humidity effect compensation.
In addition to calibrating against humidity, the team has also carried out temperature shock test on the sensor material. Although the current electronic component of the sensor device can only support up to 50 degrees Celsius, the phage sensor can withstand much higher temperature. The team has evaluated placing the phage sensor in 85 degrees Celsius temperature environment for a long period of time (up to 24 hours), and has found that there is a less than 3% reduction in signal response.
2. Sensor Fabrication Optimization
During the Phase I project period, the team also investigated sensor color consistency between different sensors, as this is useful in predicting the level of manufacturing tolerance in actual production. The team has scaled up sensor production to up to 25 sensors per batch, and evaluated the sensor consistency over a two-month period, and the results are shown in Figure 2. The team has found ~0.5% color variation between the batch.
3. Sensor Material Production Optimization
The team aimed to optimize the current production process, which is necessary before moving into bulk phage production. During the project period, the team investigated different parameters during fermentation, including bacterial culture aeration ratio and phage addition timing. However, throughout the project period, the team have determined that the current production process have too many challenges, including human error, slow production time, and low yield. The team has then moved forward to develop new production schemes to optimize the phage cultivation process through the use of commercial bioreactors. Bioreactors allow controlled fermentation in which most parameters are controlled and automated, and also helps to eliminate several parameters from the current, manual fermentation. Parameter such as the surface area to volume ratio of the culture media to the air for oxygen exchange have all but eliminated. Parameters such as temperature, agitation speed, and air flow rate are now controlled. Because of this, the team plans to move forward on the bulk manufacturing with the bioreactor system.
4. Sensor Mechanical Design
Because BioInspira's goal is to miniaturize and to lower the production cost of the sensor to meet the program requirement, the team is making continuous improvements on the sensor design.
The A8 design has reduced flow volume within the sensor chamber (the modified design is named the A8), as well as less dead volume and eliminated structural weakness of the sensor by combining the two units into one. However, we have also noted that the design is still too big and is not able to reach the cost target. We have made further improvements on the sensor design, with our new test unit. In the new design (which is named Small CIS test unit), the entire sensor is reduced to roughly 2"x2.5"x1.5". The sensor chamber is also drastically reduced, allowing faster gas exchange across the membrane. A calibration cap is also constructed to be placed on top of the sensor, in case the sensor requires active gas flow during sensor calibration. The sensor device is made of metal material because of quick turnaround (easier to machine).
Schematic of Small CIS test unit. With size of roughly 2"x 2.5"x 1.5", the test unit is at least 80% smaller than the A8 unit. The sensor chamber is covered with porous membrane to filter out dust, water, and air turbulence, and allows diffusion-based sensing, as opposed to the A8 that relies on active driven flow for sensing. An adapter calibration cap is also available to be fit on the sensor for active driven flow sensing.
Conclusions:
This Phase I project has successfully designed and miniaturized (up to six times) the sensor mechanical device and moved BioInspira closer to commercialization. Preliminary study into the phage sensor fabrication also has shown that the sensor is reproducible and stable over long duration. The team also achieved several customer outreach milestones, including initiating a paid pilot from a consortium of utilities, as well as brought on board an industry sensor veteran (executive level) to become our Chief Sensor Advisor. That being said, there are also some challenges that remain to be solved, but the team already have plans to address them in the future in the Phase II project.
The perspectives, information and conclusions conveyed in research project abstracts, progress reports, final reports, journal abstracts and journal publications convey the viewpoints of the principal investigator and may not represent the views and policies of ORD and EPA. Conclusions drawn by the principal investigators have not been reviewed by the Agency.