Table 1.
Summary of colorimetric sensing of environmental gases.
| Categories | Analytes | Sensing probes | Substrates | Humidity concerns |
|---|---|---|---|---|
| Volatile organic compounds | Hydrocarbons, alcohols, amines, ethers, aldehydes, ketones, carboxylic acids, thioethers, phosphines,phosphites, thiols, arenes, and halocarbons.36, 37, 40 | Metalloporphyrins, free-base porphyrins, pH indicators, and solvatochromic dyes.36, 37, 40 | Reverse phase silica thin-layer-chromatography plates.36, 37 | Hydrophobic dyes and substrate were selected to avoid humidity interference in 10 to >95 % RH.37 |
| Air quality related pollutants | Particulate matter, ozone, nitrogen dioxide, sulfur dioxide, carbon monoxide, and lead.24, 50, 51 | Redox indicators,50 and potassium disulfitopalladate (II).24 | Silica G TLC plates.24, 50 | The sensing performance does depend on the humidity of the ambient air.24 |
| Toxic industrial chemicals | Industrial chemicals that are manufactured, stored, transported, and used throughout the world, such as, ammonia, arsine, chlorine, diborane, dimethylamine, fluorine, formaldehyde, hydrogen chloride, hydrogen cyanide, hydrogen fluoride, hydrogen sulfide, hydrazine, methylamine, methyl hydrazine, nitric acid, nitrogen dioxide, phosgene, phosphine, sulfur dioxide, and trimethylamine, et al.41, 52, 53,54 | Sol-gel-colorant solutions,41, 52, 53 and mononuclear iron(II) neutral complex.54 | Polyethylene terephthalate (PET) film.41, 52, 53 | Hydrophobic dyes in hydrophobic matrixes rendering the sensor array much less sensitive to changes in humidity.41, 52, 53 |
| Chemical warfare agents and explosives | Nerve agents like sarin, soman, and tabun; poisons, like mustard gas, lewisite, phosgene, phosgene oxime, cyanide, mace, and ricin; explosives like TNT (2,4,6- trinitrotoluene), DNT (2,4 dinitrotoluene), HMX (octahydro-1,3,5,7-tetranitro- 1,3,5,7-tetrazocine), Tetryl (2,4,6-trinitrophenylmethylnitramine), DDNP (diazodinitrophenol), RDX (cyclotrimethylenetrinitramine), pA (picric acid), DMNB (2,3-dimethyl-2,3-dinitrobutane), and TATP (triaceonetriperoxide).7 | Functionalized gold nanoparticles;55 oxime-modified PDA (OX-PDA) liposomes;56 push-pull chromophores;57 Brady’s reagent, metal salts, pH indicators, porphyrins, redoxsensitive dyes, solvatochromic dyes, and Strong base.58 59 | Cellulose acetate membrane filter,56 silica gel plate,57 and polypropylene membranes.59 | No color changes were detected at the humidity of saturated H2O atmosphere57 due to the use of hydrophobic dyes in hydrophobic matrixes, the colorimetric sensor array is very insensitive to changes in ambient humidity.58 |
| Odors of food & beverage | Relevant volatile organic chemicals from food and beverage.5, 60 | Porphyrins and metalloporphyrins, pH indicators.5 | C2 reverse phase silica gel plates, polyvinylidene fluoride (PVDF) membrane, silica gel plates, TiO2 nanoporous film, polyvinylidene difluoride membrane, Acetate sheet.5 | The insensitivity of colorimetric sensors to changes in humidity is due to the hydrophobic dyes and hydrophobic matrixes.60 To analyze samples with high humidity, the dyes and the membrane must be hydrophobic.61 |