Unprecedented Reversible Real-Time Luminescent Sensing of H2S in the Gas Phase.

Hydrogen sulfide monitoring has become essential in the natural gas industry, biogas production, wastewater treatment plants, paper mills, sewers, and landfills of waste due to its toxic, irritating, extremely flammable, and corrosive features. However, each of the current monitoring technologies (gas chromatography, lead acetate tape, electrochemical, UV and NIR absorption) has its own limitations. Furthermore, the existing luminescent molecular probes for H2S cannot monitor it continuously due to the irreversibility of their reaction with the analyte. Herein, we report the development and application of the first reversible H2S luminescent sensor. The sensing layer capitalizes on the highly photooxidizing phosphorescent [bis(1,10-phenanthroline)(1,4,5,8-tetraazaphenanthrene)]ruthenium(II) dication immobilized on alkali-treated silica microspheres, interrogated with a dedicated fiber-optic phase-sensitive luminometer. The chemosensing mechanism is a fully reversible electron transfer from the analyte to the photoexcited dye. The H2S optosensor exhibits a 0.34-50 ppmv dynamic range, a limit of detection equal to 0.025 ppmv, repeatability, and reproducibility better than 3.2%, plus response and recovery times ( t90 and t-90) shorter than 240 s. The H2S luminescent sensor performance has been verified for more than six months in a biomethane production plant, showing an excellent stability with automatic daily maintenance.

Optimization of Temperature Sensing with Polymer-Embedded Luminescent Ru(II) Complexes.

Temperature is a key parameter in many fields and luminescence-based temperature sensing is a solution for those applications in which traditional (mechanical, electrical, or IR-based) thermometers struggle. Amongst the indicator dyes for luminescence thermometry, Ru(II) polyazaheteroaromatic complexes are an appealing option to profit from the widespread commercial technologies for oxygen optosensing based on them. Six ruthenium dyes have been studied, engineering their structure for both photostability and highest temperature sensitivity of their luminescence. The most apt Ru(II) complex turned out to be bis(1,10-phenanthroline)(4-chloro-1,10-phenanthroline)ruthenium(II), due to the combination of two strong-field chelating ligands (phen) and a substituent with electron withdrawing effect on a conjugated position of the third ligand (4-Clphen). In order to produce functional sensors, the dye has been best embedded into poly(ethyl cyanoacrylate), due to its low permeability to O2, high temperature sensitivity of the indicator dye incorporated into this polymer, ease of fabrication, and excellent optical quality. Thermosensitive elements have been fabricated thereof as optical fiber tips for macroscopic applications (water courses monitoring) and thin spots for microscopic uses (temperature measurements in cell culture-on-a-chip). With such dye/polymer combination, temperature sensing based on luminescence lifetime measurements allows 0.05 °C resolution with linear response in the range of interest (0⁻40 °C).