Bio-inspired ultrasensitive colorimetric detection of methyl isothiocyanate on nylon-6 nanofibrous membrane: A comparison of biological thiol reactivities.

Living organisms, including human beings, rapidly show skin color changes after chemical poisonings, a result of toxicological or detoxification reactions caused by biological thiol compounds. On the other side, quick and portable detection of highly-volatile toxicants is an urgent need for improving human safety and personal protection, especially real-time monitoring of fumigants at low level for protection of farm workers and residents from overexposure of fumigants, vaporous pesticides. Here, we designed a rapid and portable detection method for methyl isothiocyanate (MITC) vapor by mimicking detoxification reactions of biological thiols in human bodies with MITC. The detection reaction was implemented on a nylon-6 nanofibrous membrane with ultrahigh surface areas to show color signals with the addition of Ellman's reagent. The reactivities of glutathione, N-acetyl-L-cysteine, L-homocysteine, cysteamine, and thioglycolic acid toward MITC were experimentally explored and theoretically discussed. The detection sensitivity is tunable in different biological thiol systems, which broadens the sensor applications in detection of trace amount of MITC in ambient environment and improves the protection of human safety. The new sensor system reduced the sensor operation time to 15 min and achieved the detection limit of 99 ppb, much lower than its permissible exposure limit (220 ppb).

Colorimetric Detection of Carcinogenic Alkylating Fumigants on Nylon-6 Nanofibrous Membrane. Part I: Investigation of 4-( p-Nitrobenzyl)pyridine as a "New" Sensing Agent with Ultrahigh Sensitivity.

Alkylating fumigants are widely used in agricultural production for the control of soil-borne pests, but the acute toxicity and carcinogenicity of these chemicals pose a health threat to farm workers, as well as residents. A nanofibrous membrane-based colorimetric sensor relying on the nucleophilic substitution reaction of 4-( p-nitrobenzyl)pyridine (NBP) is introduced for the convenient and portable detection of alkylating fumigants. Comparing with the traditional use of NBP in detecting alkylating agents, this sensor system achieves a parts per billion level detection sensitivity toward alkylating fumigant gases without a high-temperature incubation or the addition of extra bases. The mechanisms of the detection reaction and the detection sensitivities of different fumigants were studied with computational methods, and the results comprehensively prove the proposed optimized detection mechanisms. The detection limit of methyl iodide, methyl bromide, and 1,3-dichloropropene successfully reaches to the limiting exposure concentrations (PEL or REL) with a naked-eye detectable color difference within 5 min with a dynamic detection procedure. The designed sensing system is promising for a real-time monitoring of the air quality related to alkylating fumigants in the environment, especially in agricultural and industrial areas.

Sensitivity-Tunable Colorimetric Detection of Chloropicrin Vapor on Nylon-6 Nanofibrous Membrane Based on a Detoxification Reaction with Biological Thiols.

Detoxification reaction of chloropicrin in the human body with biological thiols was selected for detection of chloropicrin in the air. The consumption of free sulfhydryl group in biological thiols by chloropicrin is colorimetrically detectable with the addition of the Ellman's reagent. In this study, glutathione, N-acetyl-l-cysteine, l-homocysteine, cysteamine, and thioglycolic acid were tested as sensing agents for chloropicrin vapor detection in ppb concentration range. The reactivity of the selected biological thiols was investigated based on both their redox properties and the nucleophilic strength of the sulfhydryl groups. Nylon-6 nanofibrous membrane and an organic solvent were used as a sensor matrix and a vapor sorbent, respectively, to provide solid supports with ultrahigh surface area and enhanced adsorption to chloropicrin vapor. The tunable sensitivity and detection range by using different biological thiols was achieved on the sensors due to the different reactivity of thiols toward chloropicrin.