Grantee Research Project Results
Final Report: Inexpensive Colorimetric Sensor for Formaldehyde
EPA Contract Number: EPD17030Title: Inexpensive Colorimetric Sensor for Formaldehyde
Investigators: Maruniak, Autumn
Small Business: iSense, LLC
EPA Contact: Richards, April
Phase: I
Project Period: September 1, 2017 through February 28, 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 brief describes the development of an inexpensive sensor to monitor indoor formaldehyde levels. The instrument will be capable of detecting low-ppb levels of formaldehyde in the presence of common interferents. Formaldehyde is used in manufacturing and is present in many building materials, glues, resins, and commercial products found in the residential, office, and industrial buildings. There are significant health risks associated with even low levels of formaldehyde, including eye, skin, and respiratory irritation. It is also classified as a probable human carcinogen at high or prolonged exposure. Current detection methods are expensive and bulky. This Phase I research demonstrated the feasibility of the proposed approach through fabrication of prototype sensors and by testing performance in conditions simulating contaminated indoor air. The results of these tests are being used to quantify detection limits and hardware requirements for a commercial product.
There is an acute need for development of inexpensive formaldehyde sensors. Formaldehyde is found in many building materials, including manufactured wood products, resins, insulation, glues, and paints as well as cosmetics, permanent press fabrics, and industrial disinfectants. Off-gassing of formaldehyde from these materials is the primary method of exposure indoors, although tobacco smoke and smog are also contributors. At higher concentrations (> 600 ppb), formaldehyde exposure can cause skin rashes and impact lung function. However, exposure to even small amounts of formaldehyde (100-500 ppb) may cause adverse health effects, such as irritation of the eyes, nose, throat, airways, and skin or exacerbation or asthma and allergies. Vulnerable populations (children, the elderly, and individuals with breathing problems) may be especially sensitive to formaldehyde. Consequently, the ability to detect formaldehyde at very low concentrations is critical; the World Health Organization has set a safe-exposure standard of 80 ppb averaged over 30 minutes.
Access to indoor formaldehyde sensors is useful to consumers as it allows them to take steps to reduce formaldehyde levels in their home and assess their effectiveness. While there are numerous methods for detecting and measuring gaseous formaldehyde, there remains a need for an inexpensive, sensitive, and rapid analytical technology. Many available formaldehyde-sensing technologies are not well suited to the consumer market. The sensor must be simple to operate, inexpensive, and provide readings in real-time. This precludes analytical methods that rely on multi-step mixtures of reagents, derivatization and extraction (e.g., DNPH), analyte pre-concentration or sorption, or expensive chromatographic analysis (HPLC, GC, etc.). The sensor must also be sensitive and selective for very low concentrations of formaldehyde. Electrochemical gas sensor technology accounted for 19.3% of the global gas sensors market and is expected to dominate global demand in the future. Electrochemical gas sensing is attractive because the sensors are capable of detecting multiple gases and can be cost effective. However, while electrochemical sensors are easily incorporated into portable devices and produce real-time sensor readings at low concentrations, instruments with excellent sensitivity are expensive and the sensing element is frequently affected by water vapor and other oxygenated VOCs like acetone, alcohols, and oxides of nitrogen. Additionally, the lifetime of an electrochemical sensor is also sensitive to environment and length of exposure.
Summary/Accomplishments (Outputs/Outcomes):
iSense is commercializing a proprietary sensor technology invented by Prof. Kenneth Suslick at the University of Illinois. The advantage of colorimetric sensors compared to other technologies lies in the simplicity of their design and data acquisition. The sensing element is a diverse array of chemically responsive chromo- and fluorogenic indicators embedded in highly porous host materials that optimize vapor diffusion for improved sensitivity. The overall pattern of chemically induced color change encodes the chemical composition of the gas sample presented to the sensor. While colorimetric sensing is an old technology, incorporation of many indicators into an array and measuring the composite response is a novel approach to identifying single compounds and complex mixtures. Additionally, highly specific indicators in the array can be singled out to determine concentrations of single VOCs in complex mixtures.
The iSense CSA relies on strong dye-analyte chemical interactions from five key classes of chemically-responsive dyes: (i) organometallic complexes that coordinate Lewis basic compounds, (ii) pH indicators that respond to Brønsted acidity/basicity, (iii) dyes with large permanent dipoles that respond to local polarity, (iv) redox indicators, and (v) nucleophilic indicators that respond to electrophilic analytes (Figure 1). While early generations of the array relied on commercially available or known compounds, iSense now devotes significant effort to synthesize novel, chemoselective indicators for specific analytes to improve sensitivity and selectivity. These indicators are not used in our existing array and will be incorporated into our proposed formaldehyde sensor to improve sensitivity and specificity. This broad spectrum of highly sensitive chemical interactions should allow our sensor technology to detect and correctly identify very low concentrations of formaldehyde in the presence of a variety of interferents and in different ambient conditions.
The current form factor of the iSense CSA is a single use sensor printed on paper or a thin plastic membrane, depending on application. The sensor is inexpensive to manufacture and because it is disposable it does not suffer from the lifetime issues common to other formaldehyde sensors. Imaging of the sensor is accomplished through a camera or contact-imaging sensor, as in commercial flatbed scanners. The optical response is compared to a library using proprietary software. Ease of use, cost, and ability to detect individual analytes within complex mixtures makes the iSense CSA well suited to the consumer market.
Conclusions:
Technical Objectives
The focus of Phase I was to develop a sensor for formaldehyde monitoring in indoor environments. The path to the ultimate goal is accomplished by developing the sensor array and building a library of chemical fingerprints to provide identification of formaldehyde and concentration and translate this information into an assessment of the risks to the consumer. The specific objectives of the program were as follows:
Task 1: Optimize the array for discrimination of formaldehyde.
iSense has a large library of indicators and formulations from which to draw and it keeps expanding we continue to refine our sensors. We screened new indicators from our library for formaldehyde taking into account the lessons learned from early work developing a formaldehyde sensor.
Task 2: Demonstrate sensitivity of CSA to formaldehyde from 0.05-5.0 ppm in wet and dry air.
We performed experiments in the lab to evaluate the range of sensitivity of our newly designed sensor to formaldehyde in dry air and under a variety of relative humidity environments.
Task 3: Demonstrate sensitivity of CSA to formaldehyde from 0.05-5.0 ppm with various background gases commonly found indoors.
We performed experiments in the lab to evaluate the sensitivity and selectivity of our newly designed sensor to a variety of concentrations of formaldehyde mixed in with commonly found background compounds found in indoor environments.
Task 4: Analyze data to assess the efficacy of the sensor to discriminate between different concentrations of formaldehyde with various background gases commonly found indoors.
After collected sufficient data on a set of formaldehyde concentrations, we measured the accuracy of formaldehyde discrimination.
Task 5: Produce a prototype operational for 8 h, inexpensive (cost $100).
A small chemical identification device (CID) has been developed for identification of liquid TICs and CWAs. The CID has three main parts: 1) reader, 2) spacer, and 3) disposable ticket (sensor) holder. The reader portion contains the imaging system, processor electronics, communications (WiFi, Bluetooth) and software. The disposable spacer with ticket is simply plastic and sensor. The intelligent reader portion can be completely reused and it is anticipated the reader usable life will be many years and cost to produce will less than $100. The reader includes:
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Light source: diffuse white-light LED panels
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Photodetector: high resolution RGB CCD
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11+ hour battery life
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OLED color display
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GPS, real-time clock
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WiFi, Bluetooth
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MicroUSB OTG plug for power, charging, and connecting USB peripherals
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.