Sol–gel based optical carbon dioxide sensor employing dual luminophore referencing for application in food packaging technology

Abstract

An optical sensor for the measurement of carbon dioxide in Modified Atmosphere Packaging (MAP) applications has been developed. It is based on the fluorescent pH indicator 1-hydroxypyrene-3,6,8-trisulfonate (HPTS) immobilised in a hydrophobic organically modified silica (ormosil) matrix. Cetyltrimethylammonium hydroxide was used as an internal buffer system. Fluorescence is measured in the phase domain by means of the Dual Luminophore Referencing (DLR) sensing scheme which provides many of the advantages of lifetime-based fluorometric sensors and makes it compatible with established optical oxygen sensor technology. The long-term stability of the sensor membranes has been investigated. The sensor displays 13.5 degrees phase shift between 0 and 100% CO2 with a resolution of better than 1% and a limit of detection of 0.08%. Oxygen cross-sensitivity is minimised (0.6% quenching in air) by immobilising the reference luminophore in polymer nano-beads. Cross-sensitivity towards chloride and pH was found to be negligible. Temperature effects were studied, and a linear Arrhenius correlation between ln k and 1/T was found. The sensor is stable over a period of at least seven months and its output is in excellent agreement with a standard reference method for carbon dioxide analysis.

Evaluation of a lifetime‐based optode to measure oxygen in aquatic systems

“…Optode technology has an advantage over conventional sensors in that it can also be used to assess oxygen distributions in 2 dimensions (e.g., Holst et al, 1997Holst et al, , 1998Glud et al, 1999Glud et al, Q1, 2001Glud et al, , 2005 and to detect other substances (e.g., Klimant et al, 2000;Huber et al, 2000Huber et al, , 2001aHuber et al, , 2001bHulth et al, 2002;von Bültzingslöwen et al, 2002).…”

Highly CO2sensitive extruded fluorescent plastic indicator film based on HPTS

“…[37][38][39][40][41]. One of the earliest studies reported in Table 2, used agarose as the encapsulation medium [32], but required a gas-permeable membrane to stop the film drying out and also to allow its use for making dissolved CO 2 measurements.…”

“…These films usually suffer from poor stability unless used and stored either in water or under high humidity conditions [35,37].…”

Fluorescent Carbon Dioxide Indicators

“…(9). Table 3 provides details of many of the dry luminescent optical films for carbon dioxide that have been reported in the literature [51][52][53][54][55][56][57][58][59][60][61][62][63][64][65][66][67][68][69][70] and, as with the wet indicators, reviewed earlier, see table 1, most are intensity-rather than lifetime-, based sensors. Almost all these sensors utilise the ion-pair technology developed by Mills et al 44,45 .…”

“…A brief inspection of the many examples of dry luminescent indicator systems for carbon dioxide reveals that most of those reported to date are intensity-based and, amongst the few other, and admittedly more recent, examples, the FRET method of detection dominates. One other sensing method that doesn't fall into any of the categories considered so far, is the measurement of carbon dioxide levels using phasemodulated fluorimetry coupled with a Dual Lumophore Referencing (DLR) proposed by MacCraith et al 69 . In DLR, two different luminescence signals are generated in the sensing membrane by the modulated excitating light source; in this case a bright blue 470 nm LED.…”