Our Technology

1.1.  The Motivation.

According to the US Dept. of Transportation, there are more than 22,000 reported chemical spills and related incidents annually (double the number from a decade ago), resulting in $80 million in direct damages and $6.8 billion in the economic cost from 3600 injuries and 180 deaths.  Police and firefighters are the first responders to such events. There are approximately 700,000 full time law enforcement officers (US Bur. Justice Stats., 2021) and 1,081,000 firefighters (Natl. Fire Protection Assoc.). In addition, OSHA estimates that there are >32 million workers, in some 3.5 million workplaces in the U.S. who are regularly exposed to hazardous chemicals.

Unfortunately, the current technology for detecting toxic gases is too slow (e.g., many minutes), too limited (e.g., responds to single or few analytes), too big to be portable, or much too expensive (tens of thousands of dollars) to be in regular use by first responders. The lack of portable, cost-effective solutions for monitoring individual exposures to a range of toxic industrial chemicals (TICs) presents a serious and persistent problem for these workers — there is no equivalent of a “radiation badge” for toxic gas exposure in the chemical workplace, as illustrated in Fig. 1.


Fig. 1.  Comparison of various toxic gas sensor technologies.

Iridescent Sensors is creating a field-deployable “optoelectronic nose” (Fig. 2) that will be sufficiently inexpensive to be placed in most first responder vehicles (roughly 500,000; NFPA, 2021) and in most chemical workplaces (3.5 million) in the U.S. This technology offers a significant advance in personal protection of the health and safety of millions of people exposed to toxic chemicals, in both detect-to-protect (responder safety) and detect-to-warn (community safety) applications.

Fig. 2. Our optoelectronic nose is made up of (a) an inexpensive colorimetric sensor array held (b) in a disposable cartridge and (c) a hand-held analyzer. This photo shows the 1st generation: a fully self-contained device with onboard computing and a library of array res­ponses. (d) Chemical analysis uses the pattern of color changes of an array of chemically responsive dyes before and after exposure. This pattern is a high-dimensional difference vector that is a “molecular fingerprint” unique for any chemical mixture. Patents held by UIUC are licensed by Iridescent Sensors.

The advantages of our optoelectronic nose over current chemical detectors include: (1) low production costs (projected to be <$1000 for the analyzer and <$3 for each disposable sensor array, in quantity), (2) rapid response (detection in <1 min), (3) high sensitivity to a very wide range of toxic gases, (4) excellent ability to differentiate one analyte from another, (5) low response to interferents (e.g., changes in humidity), and (6) extreme portability (size of a thick cell phone). The optoelectronic nose can quantitatively identify 100s of TICs at concentrations of practical importance, from above the IDLH (immediately dangerous to life or health, OSHA/NIOSH) to well below the PEL (permissible exposure level) with a single test.


1.2. The Innovation.  

The technology is elegantly simple: a disposable array of chemically-responsive dyes, pigments and colorants is digitally imaged before and during exposure to the analytes of interest. The pattern of color changes in the array represents a unique molecular fingerprint of the analytes. The sensor arrays are inexpensive and disposable, which avoids the traditional problems of drift and calibration associated with prior electronic nose (e-nose) technologies.

The founders of Iridescent Sensors have developed an inexpensive and versatile colorimetric sensor array and a handheld analyzer for these sensor arrays. This “optoelectronic nose” has a wide range of applications reported in more than 60 peer-reviewed journal articles, including recent highly cited publications in Acct. Chem. Res. and Chem. Rev. [1-2]. Key applications include toxic gas and VOC detection and quantification; rapid bacterial detection and antibiotic susceptibility testing; quantitation of spoiled meats, fish, and poultry; QC/QA of beverages ranging from coffees to sodas to liquors; personal hygiene; identification and fingerprinting of homemade explosives (HMEs); and detection of pollutant exposure of artwork during travel and on exhibition [3-20].  The colorimetric sensor array and the optoelectronic nose inventions are protected through an extensive patent portfolio [26-34].

Colorimetric sensor arrays are a powerful and general method to identify and classify odors, complex chemical mixtures, and toxic gases [1-2]. The fundamental scientific work enabling the Iridescent Sensors technology has received several international awards, including the 2021 Theophilus Redwood Award of the Royal Society of Chemistry, the 2021 Eastern Analytical Society Award for Outstanding Achievements in the Fields of Analytical Chemistry, and the Wolfgang Göpel Award of the International Society for Olfaction and Chemical Sensing (ISOCS).

The color changes of our colorimetric sensor arrays, quantified simply by the changes in red, green and blue values in digital images, are molecular fingerprints. The color changes of each of the sensor spots form a high-dimensional difference vector (i.e, the ΔRGB values of reach of the spots: 36 spots generates a 108-dimensional vector) that are identifiable by machine learning (ML) techniques or multivariate analysis (e.g., support vector machines, hierarchical cluster analysis) against a library of known patterns relevant to the specific group of analytes. This approach enables outstanding differentiation even among closely-related chemical mixtures: for example, one can differentiate one single-malt scotch from another, and one can even tell if the scotch has been diluted by as little as 1%! [13]

Unlike prior e-nose technologies, using metal oxide sensors or conductive polymers for example, colorimetric sensors rely on the chemical reactivity of analytes, which provides an intrinsically high-dimensional representation of analyte molecular structure, in much the same way as the receptor neurons used in mammalian olfaction [25]. For example, a database of color change patterns for 100 VOCs analyzed with principal component analysis (PCA, which maximizes differences between analytes into as few dimensions as possible) required >20 dimensions to capture 95% of the total variance. In contrast, data from prior e-noses very seldom contain more than 2 orthogonal dimensions of information, which cripples their ability to distinguish similar analytes. In addition, we utilizes hydrophobic dyes and substrates so our arrays are unaffected by changes in humidity, a serious problem in past electronic nose technologies.

Fig. 3. Twenty high hazard TICs (toxic industrial chemicals) at the IDLH (immediately dangerous to life and health). TICs chosen from the list prepared of urban hazards by the ITF-40 (Intl. Task Force #40, DoD). The differences between the patterns is obvious to the eye, even without advanced multivariate analysis or machine learning. In sept­uplicate trials, there are no statistical confusions among the 20 TICs at IDLH or between IDLH and PEL. The response time is less than 10 seconds. 

In previous laboratory results critical to this proposal, we have shown that we can differentiate the color change fingerprints of 20 high hazard toxic industrial chemicals (TICs) easily and quickly (Fig. 3), with semiquantitative analysis at concentrations above the IDLH to well below the PEL with very low error rates (<1%), using an ordinary flatbed scanner [4-7]. The goal of Iridescent Sensors is to bring the handheld analyzer [21-23] to the verge of a commercial device and to demonstrate market utility by field-testing the device for rapid detection of toxic gases relevant to first responders. 

Indeed, the optoelectronic nose can be thought of as a nearly universal tool. A wide variety of applications have already been brought to proof-of-concept in peer-reviewed scientific publications in many areas outside of HazMat, including food safety [9], industrial QC/QA (ranging from receivable chemicals [7] to beverages and liquors) [10-13], homeland security (e.g., HME identification and fingerprinting) [15-18], personal hygiene [14], monitoring fruit ripening [24], and environmental surveillance (e.g., for pollution exposure of artwork during exhibition [19-20]). The colorimetric sensor array is nearly universal once it incorporates ~40 different chemically responsive dyes: i.e., it is able to differentiate all common organic functional groups and discriminate among and identify 100 different VOCs in experimental trials [7]. Any new specific application will use the same sensor array and analyzer and then requires the relatively simple task of acquiring a different library of responses relevant to that application.


References (to download pdf files of these papers, go to https://suslick.scs.illinois.edu/smell_seeing.html)


    1. Zheng, L.; Askim, J. R.; Suslick, K. S. "The Optoelectronic Nose: Colorimetric and Fluorometric Sensor Arrays“ Chem. Rev., 2019, 119, 231-292.
    2. Li, Z.; Suslick, K. S. "The Optoelectronic Nose“  Accts. Chem. Res., 2021, 54, 950-960.
    3. Rakow, N. A.; Suslick, K. S. "A Colorimetric Sensor Array for Odour Visualization" Nature, 2000, 406, 710-714. 
    4. Feng, L.; Musto, C.J.; Kemling, J. W.; Lim, S.H.; Suslick, K. S. "A Colorimetric Sensor Array for Identification of Toxic Gases below Permissible Exposure Limits" Chem. Commun., 2010, 46, 2037-2039.
    5. Lim, S. H.; Feng, L.; Kemling, J. W.; Musto, C. J.; Suslick, K. S. "An Optoelectronic Nose for Detection of Toxic Gases" Nature Chemistry, 2009, 1, 562-567.
    6. Feng, L.; Musto, C.J.; Kemling, J. W.; Lim, S.H.; Zhong, W.; Suslick, K. S. "Colorimetric Sensor Array for Determination and Identification of Toxic Industrial Gases"  Anal. Chem., 2010, 82, 9433-9440.
    7. Janzen, M. C.; Ponder, J. B.; Bailey, D. P.; Ingison, C. K.; Suslick, K. S. "Colorimetric Sensor Arrays for Volatile Organic Compounds" Anal. Chem. 2006, 78, 3591-3600.
    8. a. Carey, J. R.; Suslick, K. S.; Hulkower, K.; Imlay, J. A.; Imlay, K.; Ingison, C.K.; Ponder, J. B.; Sen, A.; Wittrig, A. E. "Rapid Identification of Bacteria with a Disposable Colorimetric Sensor Array" J. Am. Chem. Soc. 2011, 133, 7571-7576.
      b. Zhang, Y.; Askim, J. R.; Zhong, W.; Orlean, P.; Suslick, K. S. "Identification of pathogenic fungi with an optoelectronic nose" Analyst, 2014, 139, 1922-1928. DOI: 10.1039/C3AN02112B
    9.  Li, Z.; Suslick, K. S. "Portable Optoelectronic nose for Monitoring Meat Freshness" ACS Sensors, 2016, 1, 1330-1335. DOI: 10.1021/acssensors.6b00492
    10. Zhang, C.; Bailey, D. P.; Suslick, K. S. “Colorimetric Sensor Arrays for the Analysis of Beers: A Feasibility Study” J. Agric. Food Chem., 2006, 54, 4925-4931
    11.  Zhang, C.; Suslick, K. S. "Colorimetric Sensor Arrays for Soft Drink Analysis" J. Agric. Food Chem., 2007, 55, 237-242.
    12. Suslick, B. A.; Feng,L.; Suslick, K. S. "Discrimination of Complex Mixtures by a Colorimetric Sensor Array: Coffee Aromas" Anal. Chem., 2010, 82, 2067-2073.
    13. Li, Z.; Suslick, K. S. "A Hand-Held Optoelectronic Nose for the Identification of Liquors" ACS Sensors, 2018, 3, 121-127.
    14. Li, Z.; Li, H.; LaGasse, M. K.; Suslick, K. S. "Rapid Quantification of Trimethylamine" Anal. Chem., 2016, 88, 5615-5620. DOI: 10.1021/acs.analchem.6b01170
    15. Lin, H.; Suslick, K. S. "A Colorimetric Sensor Array for Determination of Triacetone Triperoxide Vapor" J. Am. Chem. Soc., 2010, 132, 15519-15521.
    16. Askim, J. R.; Li, Z.; LaGasse, M. K.; Rankin, J. M.; Suslick, K. S. "An optoelectronic nose for identification of explosives" Chem. Sci., 2016, 7, 199-206.   
    17. Li, Z.; Jang, M.; Askim, J. R.; Suslick, K. S. "Identification of accelerants, fuels and post-combustion residues using a colorimetric sensor array" Analyst 2015, 140, 5929-5935. DOI: 10.1039/c5an00806a 
    18. Li, Z.; Bassett, W. P.; Askim, J. R.; Suslick, K. S. "Differentiation among peroxide explosives with an optoelectronic nose" Chem. Commun. 2015, 51, 15312-15315. DOI: 10.1039/C5CC06221G
    19. LaGasse, M. K.; McCormick, K.; Li, Z.; Khanjian, H.; Schilling, M.; Suslick, K. S. "Colorimetric Sensor Arrays: Development and Application to Art Conservation" J. Amer. Inst. Conservation 2018, 57, 127-140. https://doi.org/10.1080/01971360.2018.1495480
    20. Li, Z.; Wang, Z.; Khan, J.; LaGasse, M. K.; Suslick, K. S. "Ultrasensitive Monitoring of Museum Airborne Pollutants using a Silver Nanoparticle Sensor Array" ACS Sensors, 2020, 5, 2783-2791. https://doi.org/10.1021/acssensors.0c00583
    21. Askim, J. R.; Suslick, K. S. "Hand-Held Reader for Colorimetric Sensor Arrays"  Anal. Chem. 2015, 87, 7810-7816.  
    22. Suslick, K. S.; Askim, J. R. "Portable device for colorimetric or fluorometric analysis, and method of conducting colorimetric or fluorometric analysis" U.S. Patent 10,539,508; Jan. 21, 2020.
    23. Suslick, K. S.; Askim, J. R. "Portable device for colorimetric or fluorometric analysis, and method of conducting colorimetric or fluorometric analysis" U.S. Patent 11,035,800; June 15, 2021.
    24. Li, Z.; Suslick, K. S. "Colorimetric Sensor Array for Monitoring CO and Ethylene" Anal. Chem., 2019, 91, 797-802. https://doi.org/10.1021/acs.analchem.8b04321
    25. Wang, J.; Luthey-Schulten, Z.; Suslick, K. S. "Is the Olfactory Receptor A Metalloprotein?" Proc. Natl. Acad. Sci. U.S.A., 2003, 100, 3035-3039.
    26. Suslick, K. S.; Rakow, N. A. "Colorimetric Artificial Nose Having an Array of Dyes and Method for Artificial Olfaction" U.S. Patent 6,368,558; April 9, 2002.  
    27. Suslick, K. S.; Rakow, N. A.; Sen, A. "Colorimetric Artificial Nose Having an Array of Dyes and Method for Artificial Olfaction: Shape Selective Sensors" U.S. Patent 6,495,102 B1; Dec. 17, 2002.
    28. Suslick, K. S.; Rakow, N. A.; Sen, A. "Colorimetric Artificial Nose Having an Array of Dyes and Method for Artificial Olfaction" European Patent EP1274983; Dec. 22, 2004.
    29. Suslick, K. S.; Rakow, N.A.; Sen, A. "Colorimetric Artificial Nose having an Array of Dyes and Method for Artificial Olfaction" Indian Patent 209296; August 23, 2007.
    30. Suslick, K. S.; Rakow, N. A.; Sen, A.; McNamara, W. B. III; Kosal, Margare E. "Colorimetric Artificial Nose having an Array of Dyes and Method for Artificial Olfaction" U. S. Patent 7,261,857; August 28, 2007.
    31. Suslick, K. S.; Placek, M. J.; McNamara, W. B.; Sen, A.; Carey, J. R.; Wilson, J. B.; Keso, C. K. "Apparatus and Method for Detecting and Identifying Microorganisms" U.S. Patent Appl.  2008/0199904; Aug. 21, 2008.
    32. Suslick, K. S.; Rakow, N. A.; Sen, A. "Colorimetric Artificial Nose" European Patent 1274983 (01920627.5); February 1, 2012.
    33. Suslick, K. S.; Placek, M. J.; McNamara, W. B.; Sen, A.; Carey, J. R.; Wilson, J. B.; Keso, C. K. "Apparatus and Method for Detecting and Identifying Microorganisms" U.S. Patent 8,852,504; Oct. 7, 2014.
    34. Suslick, K. S.; Placek, M. J.; McNamara, W. B.; Sen, A.; Carey, J. R.; Wilson, J. B.; Keso, C. K. "Apparatus and Method for Detecting and Identifying Microorganisms" U.S. Patent 9,249,446; Feb. 2, 2016.
    35. Lim, S. H.; Musto, C. J.; Feng, L.; Kemling, J. W.; Suslick, K. S. "Colorimetric Sensor Arrays Based on Nanoporous Pigments" European Patent EP2331952; June 15, 2016.
    36. Suslick, K. S.; Placek, M. J.; McNamara, W. B.; Sen, A.; Carey, J. R.; Wilson, J. B.; Keso, C. K. "Apparatus and Method for Detecting and Identifying Microorganisms" U.S. Patent 9,856,446; Jan. 2, 2018.
    37. Lim, S. H.; Musto, C. J.; Feng, L.; Kemling, J. W.; Suslick, K. S. "Colorimetric Sensor Arrays Based on Nanoporous Pigments" U.S. Patent 9,880,137; Jan. 30, 2018.
    38. Suslick, K. S.; Askim, J. R. "Portable device for colorimetric or fluorometric analysis, and method of conducting colorimetric or fluorometric analysis" U.S. Patent 10,539,508; Jan. 21, 2020.
    39. Lim, S. H.; Musto, C. J.; Feng, L.; Kemling, J. W.; Suslick, K. S. "Colorimetric Sensor Arrays Based on Nanoporous Pigments" U.S. Patent 10,890,569; Jan. 12, 2021.
    40. Suslick, K. S.; Askim, J. R. "Portable device for colorimetric or fluorometric analysis, and method of conducting colorimetric or fluorometric analysis" U.S. Patent 11,035,800; June 15, 2021.
    41. Suslick, K.S.; Hinman, J. J. "Polymer Microcolumn for Gas or Vapor Separation, Chromatography, and Analysis" U.S. Patent 11,047,836; June 29, 2021.
    42. Suslick, K. S.; Li, Z.; LaGasse, M. K. Methods and devices for detection of trimethylamine (TMA) and trimethylamine oxide (TMAO) U.S. Patent 11,346,829; May 31, 2022.