Emission-based optical carbon dioxide sensing with HPTS in green chemistry reagents: room-temperature ionic liquids

Abstract

We describe the characterization of a new optical CO(2) sensor based on the change in the fluorescence signal intensity of 8-hydroxypyrene-1,3,6-trisulfonic acid trisodium salt (HPTS) in green chemistry reagents--room-temperature ionic liquids (RTILs). As far as we are aware, this is the first time RTILs, 1-methyl-3-butylimidazolium tetrafluoroborate (RTIL-I) and 1-methyl-3-butylimidazolium bromide (RTIL-II), have been used as matrix materials with HPTS in an optical CO(2) sensor. It should be noted that the solubility of CO(2) in water-miscible ionic liquids is approximately 10 to 20 times that in conventional solvents, polymer matrices, or water. The response of the sensor to gaseous and dissolved CO(2) has been evaluated. The luminescence intensity of HPTS at 519 and 521 nm decreased with the increasing concentrations of CO(2) by 90 and 75% in RTIL-I and RTIL-II, respectively. The response times of the sensing reagents were in the range 1-2 min for switching from nitrogen to CO(2), and 7-10 min for switching from CO(2) to nitrogen. The signal changes were fully reversible and no significant hysteresis was observed during the measurements. The stability of HPTS in RTILs was excellent and when stored in the ambient air of the laboratory there was no significant drift in signal intensity after 7 months. Our stability tests are still in progress.

Applications of Ionic Liquids for the Development of Optical Chemical Sensors and Biosensors

“…1.4) 81 and reservoir-type sensors. 93,94 Unlike the CO2 sensors described above, 75,76,81 the reservoir-type optical systems had no polymeric matrix. They included a cuvette that was filled with a sensing cocktail IL-BTB (or IL-HPTS) with the additive of a base (NaHCO3 or TBAOH).…”

“…81 The sensitivity of the CO2 sensors depended on the indicator pKa, the nature of the counterion of IL, and the nature of the base used in the internal buffer solution. 81,93,94 So, in colorimetric IL-emulsion-based sensors, the range of CO2 content was wider when TB but not BTB was used (Table S1). A significantly higher fluorescent response of HPTS toward CO2 in the same type of CO2-sensor with [BMIm]Tos compared to [BMIm]BF4 was attributable to higher gas solubility in the IL with a more bulky anion, Tos -.…”

“…This fact was explained by the catalytic effect of fluoride ion from BF4 -on bicarbonate formation. 94 …”

“…The use of ILs provides both high and low CO2 concentration determination. 51,75,76,81,82,94 The colorimetric sensor with [BMIm]BF4 and pH-indicator BT in a silicone matrix allows the semi-quantitative determining of 2% CO2 and lower concentrations in the gas phase. 81 The sensor based on the same matrix, but with the fluorescent indicator HPTS dissolved in [BMIm]Tos allows detecting up to 20% gaseous CO2.…”

“…Finally, the reservoir-type design sensing system, in which IL serves as a solvent for both recognition element and analyte, provides the sensitive determination of both gaseous and dissolved CO2 over a period longer than 7 months. 94 The developed SPR sensor for CO2 determination with its miniature gas detection scheme is extremely useful for environmental analysis. 82 Three O2-sensors, which serve the purpose of environmental and biomedical analysis are fabricated with IL addition to TEOS sol-gel, EC and PMMA matrices (Table S1).…”