Recently, Yuan Liu and Sadik Antwi-Boampong of the Department of Chemistry published a paper entitled “Detection of Secondhand Cigarette Smoke via Nicotine Using Conductive Polymer Films” in collaboration with their advisor, Joseph J. BelBruno, Mardi A. Crane-Godreau of the Department of Microbiology and Immunology, and Susanne E. Tanski of the Department of Pediatrics and the Dartmouth-Hitchcock Norris Cotton Cancer Center. The paper, published in Nicotine and Tobacco Research, described a sensor that the group had developed that detects levels of secondhand and even thirdhand smoke.
In the sensor, a polyaniline polymer is coated onto a chrome and nickel electrode grid, creating a conductive layer. The polymer is then protonated with acid, which then interacts with nicotine (a base), and resistance is measured across the sensor. Measurements are taken in a smoking machine, where cigarettes are spun and smoked, and the smoke is then shuttled into the exposure chamber, where the sensor is located. After each round of secondhand smoke exposure, the sensor is regenerated with purges of fresh air. The sensor is so sensitive that it even picks up levels of thirdhand smoke (smoke that has been absorbed onto surfaces such as walls, furniture, clothing, etc.).
Liu, Antwi-Boampong, and their collaborators have developed this sensor and its program interface to be used for commercial purposes to test levels of second and thirdhand smoke in homes, especially where children live. The sensor is innovative because it measures data in real-time, as compared to other sensors, which can only analyze data after full collection.
Molly Croteau, also a PhD student in the Department of Chemistry, recently sat down with Antwi-Boampong to learn more about this innovative project.
Molly Croteau (MC): How did you and Liu come to work on this project?
Sadik Antwi-Boampong (SA): This is Liu’s thesis research, and I assisted him. Our advisor, Professor BelBruno, had the idea to build this sensor.
MC: How long have you been working on this project?
SA: We’ve been researching this sensor for about three and a half years.
MC: Three and a half years is a long time—the public only sees the results. What were some of the biggest obstacles to overcome?
SA: We invested a considerable amount of time in material selection and sensor design because we wanted a simple but effective device. Once we had chosen a polymer, we then had to optimize it to provide maximum efficiency. We also had to choose a substrate and electrodes that would work well as the sensor platform. We actually started with a glass substrate, but ultimately decided against it because of its fragility and difficulty in machining. In the end, we switched to a silicon substrate with a chromium-nickel interdigitated electrode grid fabricated using conventional lithography. We also had to figure out the best solvent and optimal film thickness for the sensor layer. Thus, in our materials approach for this work, the design and selection of materials posed some challenges.
MC: The paper mentions that this sensor measured 0.75 ppb nicotine for 2 cigarettes smoked, and 1.11 ppb for 3 cigarettes smoked. What is the safe value for nicotine exposure?
SA: The median lethal dose for nicotine is about 30 mg, and as you would expect, systemic exposure to minute levels of nicotine through secondhand smoke aerosol can have serious effects on an individual. Therefore, we are really happy that our sensor is sensitive enough to measure in the ppb range.
MC: How would the user regenerate the sensor?
SA: A jet of air can fully regenerate the sensor for multiple uses.
MC: The system is relatively inexpensive—the sensor/chip costs about $30, and the computer costs anywhere from $25 to $300. In addition, the sensor can be regenerated for multiple uses. How else is your system better than what is already out there for secondhand smoke detection?
SA: In addition to being considerably cheaper, our sensor is significantly more sensitive and user-friendly than the traditional sensors already on the market. Our sensor measures data in real-time and gives that information right away to the user. Detection systems out there now only collect the data, and then it needs to be analyzed by experts and sent back to the user. Our sensor would allow the user to see right away the levels of secondhand smoke that they are being exposed to.
MC: This project involved a lot of components and different areas of research. Have you collaborated with anyone?
SA: Oh, yes. Professor Mardi Crane-Godreau works with us in our smoking chamber experiments at Dartmouth-Hitchcock Medical Center. Dr. Susanne Tanski is a pediatrician, who will be working with us to collect data from her patients who have parents who are smokers. We also collaborated with the Thayer School of Engineering on our early glass sensor fabrication and lithography work, the Dartmouth Electron Microscope Facility in Remsen on obtaining microscopic images of our sensors, the Computer Science Department on coding the program for the sensor, and the Department of Physics and Astronomy on the circuitry of the sensor. This project was very cross-disciplinary.
MC: What are your future plans for this project?
SA: Right now we are currently enhancing the sensor for selectivity and sensitivity. We are looking into different sensor layer architectures and actively exploring different ways we can make the sensor better. Also, we are looking into detecting levels of cotinine, which is what nicotine is converted to in your body. We have partnered with Professor Crane-Godreau to conduct new experiments to qualitatively and quantitatively demonstrate the sensor’s efficacy.
MC: It sounds like you are really on your way to helping people quickly monitor secondhand smoke levels.
SA: We are! In addition, I am also working on a sensor that can detect levels of formaldehyde, a ubiquitous molecule that leaches from construction materials and many household products. It has recently been determined that formaldehyde causes a variety of cancers, including myeloid leukemia, so that is the motivation for the project. There are no affordable sensor systems now that can effectively and selectively detect formaldehyde, so I am hoping to use a simple materials chemistry approach to construct a sensor that can sense formaldehyde vapor in real-time.
To read more about Liu and Antwi-Boampong’s research, see the Dartmouth Now.
by Molly Croteau