Editorial pubs.acs.org/acssensors
Adding New Senses to Your Cell Phone: Opportunities for Gas Sensing
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high specificity often comes at the cost of irreversibility, which limits many colorimetric sensors to one-time use only. Metal oxide sensors (DOI: 10.1021/acssensors.6b00477), including two-dimensional (DOI: 10.1021/acssensors.6b00801) and nanostructured metal oxides (DOI: 10.1021/acssensors.6b00597), are solid-state devices and relatively easy to miniaturize and integrate into cell phones. They typically operate at high temperatures, which demand high power (DOI: 10.1021/acssensors.6b00364). Their selectivity and long-term stability also require further improvement (DOI: 10.1021/ acssensors.6b00508, DOI: 10.1021/acssensors.6b00323). Gas sensor companies (e.g., Cambridge CMOS Sensors Ltd.) have plans to produce metal oxide sensors for cell phones. There are many chemicals in the air we inhale and exhale. Detecting, identifying, and quantifying each of them is challenging, but may not be necessary for many applications. Electronic noses, or related concepts, represent an interesting strategy that imitates human chemical senses (DOI: 10.1021/ acssensors.6b00492). Another solution is a broadband approach that detects the total of many different chemicals. Photoionization detectors are a successful portable sensor that detects total volatile organic compounds (VOCs) in air by ionizing the VOCs with a UV lamp, and detecting the associated ionic current. While popular, the UV lamp is still expensive and bulky. No matter what strategy is used, addressing an unmet need (DOI: 10.1021/acssensors.6b00288), and providing a value to the user, is just as important as improving the sensor performance. Despite advances in recent decades, adding chemical senses to cell phones is still challenging. In addition to being sensitive and selective, the sensor must be low cost, low power, miniaturized, calibration free, and tolerant of temperature and humidity variability. Today’s chemical sensors are either too bulky and expensive to fit into a cell phone, or too inaccurate and unreliable to be really useful. There is plenty of room to create new sensing technologies for the next generation of cell phones. ACS Sensors welcomes innovative sensing solutions that address clear unmet needs.
ell phones are now in the hands of billions of people, and are indispensable tools for most of us. In addition to communication, cell phones have many other functions, including photo taking, video recording, voice recognition, navigation, and physical activity tracking. These functions are all enabled by various sensors. A typical cell phone of today has more than a dozen sensors, including CMOS imagers, RGB light sensor, Hall sensor, geomagnetic sensor, accelerometer, gyro sensor, microphones, temperature sensor, proximity sensor, touchscreen, barometer, and humidity sensor. These sensors allow the cell phone to interact with both humans and the world via sound, light, gesture, and touch. While impressive, they are all physical sensors; none of them detect chemicals. Humans have five basic sensesincluding sight, touch, hearing, smell, and tasteand your cell phone has only the first three. Smell and taste are still missing. Yet, the world is made of molecules. The capability of detecting and identifying chemicals will add new “senses” to cell phones and allow them to “smell” and “taste” the chemical world around us quantitatively, complementing and enhancing the qualitative chemical sensing of our noses and tongues. Cell phones, with this capability, could detect early signs of diseases via chemical and biological markers, alert us to avoid allergens and toxicants in air, monitor environmental pollutants, and sense the danger of chemical and biological warfare agents. The opportunity is great, but the challenge is also formidable! One well established sensing strategy is to separate chemicals based on the size or other properties of the molecules, and then detect each of them with a detection technology. Gas chromatography (GC) is based on this principle. Portable GC instruments are commercially available, but they cannot fit into a cell phone yet. Another approach is based on optical spectroscopy (DOI: 10.1021/acssensors.6b00428, DOI: 10.1021/acssensors.6b00469). Miniaturized spectrometers have been introduced to the market. The most successful end consumer product (e.g., Withings’ scale) is perhaps a carbon dioxide sensor, which is based on the detection of optical absorption with infrared light emitting and detection diodes. The sensor is still expensive and prone to humidity interference, and there is a general need to invent better carbon dioxide sensors. Electrochemical sensors are particularly attractive because they directly convert chemical information (reactions) into an electronic signal. Not everything is electroactive and differentiable electrochemically, but the list of chemicals that can be detected with an electrochemical sensor is expanding (DOI: 10.1021/acssensors.6b00603, DOI: 10.1021/acssensors.6b00496). Efforts have been devoted to miniaturizing electrochemical sensors, but overcoming issues, such as tolerance to varying temperature and humidity, requires further innovation. Colorimetry detects color changes associated with a specific reaction of an analyte with a sensing material. Using a CMOS imager, a colorimetric sensor could interrogate many sensing elements in a single snapshot. The © 2017 American Chemical Society
Nongjian Tao, Associate Editor
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Arizona State University, Tempe, Arizona, United States
AUTHOR INFORMATION
Notes
Views expressed in this editorial are those of the author and not necessarily the views of the ACS.
Received: March 9, 2017 Published: March 24, 2017 317
DOI: 10.1021/acssensors.7b00147 ACS Sens. 2017, 2, 317−317
