Final Report: Multi-Analyte Nanoelectronic Air Pollutant SensorsEPA Contract Number: EPD04045
Title: Multi-Analyte Nanoelectronic Air Pollutant Sensors
Investigators: Star, Alexander
Small Business: Nanomix Inc.
EPA Contact: Manager, SBIR Program
Project Period: March 1, 2004 through August 31, 2004
Project Amount: $70,000
RFA: Small Business Innovation Research (SBIR) - Phase I (2004) RFA Text | Recipients Lists
Research Category: Nanotechnology , SBIR - Nanotechnology , Small Business Innovation Research (SBIR)
The longer term objective of the project is to develop and commercialize nanoelectronic chemical sensors for the detection and measurement of air pollution. The end result of this research will be a tiny, low cost nanosensor chip that can measure relevant concentrations of three different gaseous analytes, potentially down to the single molecule level. This activity is an extension of the gas sensing technology developed at Nanomix using carbon nanotube sensing arrays. Nanomix’s nano-enabled sensing technology promises to apply its intrinsic advantages of small size, low power consumption and low cost – to improve air pollution measurement. A sensor built upon a nanoelectronic platform is a viable and real solution for non-point source pollutant monitoring. The opportunity to deploy tiny, battery operated sensors built to identify multiple analytes and capable of wireless network integration is an exciting concept. These nanosensors can be used to catalog and monitor fugitive emissions, detect leaks from manufacturing operations, storage tanks and pipelines, and measure worker exposure in real-time.
The specific objective of the Phase I project is to build and demonstrate a nanosensor prototype to detect and measure real-time concentrations of three types of analytes: aromatic hydrocarbons, acidic gases (e.g., HCl, HF, SOx, NOx) and basic gases (e.g., NH3). The sensor itself consists of two major components: a transducer array made of single wall carbon nanotubes on a CMOS silicon substrate and chemical recognition layers or coatings that increase the transducer’s sensitivity and selectivity to the target analytes. There are three main activities covered within the initial Phase I project: 1) the selection of a recognition chemistry for each analyte, 2) sensor array fabrication, and 3) testing in a laboratory environment. To this end, Nanomix leveraged its expertise in its sophisticated carbon nanotube transducer architecture.
Nanoelectronic sensing technology promises to offer an order of magnitude reduction in the cost of the sensor components, enabling sensor deployment on a much wider scale. Successful commercialization of the technology will allow designers to place air pollution sensors anywhere and everywhere they are needed for leak detection and air quality monitoring, thus enabling ubiquitous monitoring of chosen areas. This innovation will bring significant improvements in the detection and monitoring of hazardous air pollutants and will help EPA fulfill its mission to protect human health and safeguard the natural environment.
The first major effort towards construction of the multi-analyte sensor array was the discovery of relevant recognition chemistries and depositions procedures. From a general perspective, sensor array elements must have differing degrees of sensitivity or in some cases preferential selectivity to the gas analytes of interest. For optimizing the chemical modifications to our underlying nanotube architecture, Nanomix screened various organic and inorganic materials for their activity to a range of possible analytes. These gases included volatile organic compounds (VOCs), acidic, and basic gases. The program called for initial testing of single sensor chips but this process was expedited by use of a sophisticated multiplexed testing system that allowed interrogation of up to 120 distinct, active sensors. Once the data was collected in a database, the results could be analyzed and particular materials could be chosen for their superior sensing properties. Specifically, many potential metal and polymeric functionalizations were tested, analyzed, and ultimately selected or dismissed. Techniques for localization of the chemistries followed with the aim of placing up to 4 or more distinct modifications on a single sensor chip.
The second task covered fabrication of a sensor array chip that could be integrated and potentially tested as a complete unit. Nanomix developed a functionalization procedure that allow sensor array construction. Beginning with Nanomix’s base nanotube transducer chips, each individual element was successfully modified with various metals in a controlled and robust fashion. A sensor array, for the purposes of the Phase I activities, comprised 4 different inorganic sensing elements combined with 1 unmodified, bare nanotube element, thus giving a total of 5 differently responding sensors all located within a single chip. An apparatus was conceived and built to accept and run such a complex sensor array chip. This parallel measurement system (PMS) was employed to measure all active elements continuously, in real-time, and especially during exposure to various gas flows
The final goal was to pass different analytes over the Nanomix sensor array and resolve signatures for the given gases, thereby identifying them. In a laboratory setting, various gases were delivered to the surface of the sensor array. Response data was collected in a method as to negate the bias associated with poisoning and nonrandom sampling. The data stream was then filtered and processed through principal component analysis (PCA) to recognize the signature associated with each gas analyte. This activity was the culmination of 6 months of discovery and research that lead to a proof of concept device, the Nanomix multi-analyte sensor array.
Nanomix has succeeded in fabrication of a sensor array chip that can distinguish three gas analytes. By taking advantage of its carbon nanotube transducer technology in combination with well-chosen recognition chemistries, Nanomix is on track to deliver a commercial sensor array solution. These systems will provide high sensitivity, use low power, and are intrinsically tiny, all requisites for ubiquitous sensor networks that will protect our health and the safety of the environment.