We have developed a simple colorimetric sensor array (CSA) for the detection of a wide range of volatile analytes and applied it to the detection of toxic gases. The sensor consists of a disposable array of cross-responsive nanoporous pigments whose colors are changed by diverse chemical interactions with analytes. Although no single chemically responsive pigment is specific for any one analyte, the pattern of color change for the array is a unique molecular fingerprint. Clear differentiation among 19 different toxic industrial chemicals (TICs) within two minutes of exposure at IDLH (immediately dangerous to life or health) concentration has been demonstrated. Quantification of each analyte is easily accomplished based on the color change of the array, and excellent detection limits have been demonstrated, generally below the PELs (permissible exposure limits). Identification of the TICs was readily achieved using a standard chemometric approach, i.e., hierarchical clustering analysis (HCA), with no misclassifications over 140 trials.

A low-cost yet highly sensitive colorimetric sensor array for the detection and identification of toxic industrial chemicals (TICs) has been developed. The sensor consists of a disposable array of cross-responsive nanoporous pigments whose colors are changed by diverse chemical interactions with analytes. Clear differentiation among 20 different TICs has been easily achieved at both their IDLH (immediately dangerous to life or health) concentration within 2 min of exposure and PEL (permissible exposure limit) concentration within 5 min of exposure with no errors or misclassifications. Detection limits are generally well below the PEL (in most cases below 5% of PEL) and are typically in the low ppb range. The colorimetric sensor array is not responsive to changes in humidity or temperature over a substantial range. The printed arrays show excellent batch to batch reproducibility and long shelf life (greater than 3 months).

A colorimetric sensor array has been developed for the rapid and sensitive detection of 20 toxic industrial chemicals (TICs) at their PELs (permissible exposure limits). The color changes in an array of chemically responsive nanoporous pigments provide facile identification of the TICs with an error rate below 0.7%.Chemists have no equivalent of the physicists' radiation badge: there is no readily available general purpose method to easily measure the low levels of personal exposure that workers may receive to the diverse range of volatile TICs used in laboratories, manufacturing facilities, or general storage areas. 1,2 There are numerous conventional methods 2 for the detection of gas phase hazardous chemicals, including GC/MS, 3 IMS, 4 electronic nose technologies, 5 and of course colorimetric detectors tailored to specific single analytes. 2 Most such detection technologies, however, suffer from severe limitations: GC/MS is expensive and non-portable; IMS has limited chemical specificity; and electronic nose technologies have restricted selectivity, sensitivity, and resistance to environmental interference (e.g., humidity).In recent years, we have developed a rather different optoelectronic technique using colorimetric sensor arrays made from chemically responsive dyes. This array approach 6,7 is based on strong dye-analyte interactions and differs from other electronic nose technologies that generally rely on the weaker and less specific intermolecular interactions (i.e., van der Waals and physical adsorption). The chemically responsive dyes in our colorimetric array include (1) metal ion containing dyes (e.g., metalloporphyrins) that respond to Lewis basicity, (2) pH indicators that respond to Brønsted acidity/basicity, (3) vapochromic/solvatochromic dyes that respond to local polarity, and (4) metal salt redox indicators (see ESI, † Fig. S1).We have very recently improved our array methodology by the use of chemically responsive nanoporous pigments created from the immobilization of dyes in organically modified siloxanes (ormosils). 8, 9 Porous sol-gel glasses provide excellent matrices for colorants due to high surface area, relative inertness in both gases and liquids, good stability over a wide range of pH, and optical transparency. In addition, the physical and chemical properties of the matrix (e.g., hydrophobicity, porosity) can be easily modified by changing the sol-gel formulations. NIH-PA Author ManuscriptNIH-PA Author Manuscript NIH-PA Author ManuscriptThe use of nanoporous pigments significantly improves the stability and shelf-life of the colorimetric sensor arrays and permits direct printing onto non-permeable polymer surfaces. 9,10 Additionally, we observe that the porous matrix serves as a preconcentrator thereby improving the overall sensitivity. 10 We report here the application of colorimetric sensor arrays to the identification and semiquantitative analysis of toxic industrial chemicals at their PELs and demonstrate limits of recognition below 5% of the PELs. We chose 20 repre...

A colorimetric detection method using amine functionalized polymer films doped with a pH indicator has been developed for the rapid, sensitive and quantitative detection of gaseous formaldehyde at concentrations well below the IDLH (immediately dangerous to life or health). In one minute, visible color changes are easily observed even down to the PEL (permissible exposure limit) at 750 ppb. The limit of detection is below 50 ppb (7% of PEL) after 10 min exposure. This sensor is essentially unaffected by changes in humidity or temperature (4 to 50 °C) and is not sensitive to common interferents.Formaldehyde is widely used in the manufacture of many resins, polymers, and construction materials. The thermal or chemical decomposition of such materials, however, occurs surprisingly readily from urea-formaldehyde foam insulation, particle board and formaldehyde-based resins.1 Formaldehyde is a probable human carcinogen, allergenic, and an intense irritant of eyes and mucous membranes and is therefore highly problematic as an indoor pollutant.1 -3 The ability to detect formaldehyde at very low concentrations is critical: the World Health Organization has set a standard for safe exposure of 80 ppb averaged over 30 minutes; 2 for comparison, OSHA has set the permissible exposure level (PEL) to 750 ppb and the immediately dangerous to life or health (IDLH) level at 20 ppm. 3 While there are numerous methods for detecting and measuring gaseous formaldehyde, there remains a need for an inexpensive, sensitive and rapid analytical technology. Past analytical approaches include relatively expensive instrumentation4 (e.g., electrochemical, gas chromatography, optical, chemiluminescence, etc), but also inexpensive colorimetric methods, which see some field use.5 A number of colorimetric or fluorometric methods for the detection of formaldehyde have been proposed,5 e.g., hydrazones, triazoles, pararosaniline, etc. These prior methods are generally relatively slow (typically >30 min), often cumbersome and NIH-PA Author ManuscriptNIH-PA Author Manuscript NIH-PA Author Manuscript multistep, and frequently lack sensitivity. Thus, there remains a pressing need for the development of a rapid, sensitive and highly convenient formaldehyde detection method. Herein, we report a simple and highly sensitive colorimetric method for fast formaldehyde detection.Most colorimetric formaldehyde detection methods are based on nucleophilic addition of an amine to the aldehyde forming an imine via a carbinolamine intermediate, as shown in Scheme 1. For an appropriate choice of the primary amine (e.g., delocalized conjugated substituents), the imine formation generates a color change, and so great effort has gone into the synthesis of sophisticated self-indicating primary amines. 5In contrast, we find that it is better and easier to use a simple pH indicator to detect the change in basicity upon the reaction of a non-volatile primary amine with formaldehyde. An amineterminated polymer was used to create a reactive matrix for formaldehyde d...