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Ultra-sensitive optical oxygen sensors for characterization of nearly anoxic systems.

Lehner P, Staudinger C, Borisov SM, Klimant I - Nat Commun (2014)

Bottom Line: The sensitivity of the new sensors is improved up to 20-fold compared with state-of-the-art analogues.The limits of detection are as low as 5 p.p.b., volume in gas phase under atmospheric pressure or 7 pM in solution.The sensors enable completely new applications for monitoring of oxygen in previously inaccessible concentration ranges.

View Article: PubMed Central - PubMed

Affiliation: Institute of Analytical Chemistry and Food Chemistry, Graz University of Technology, NAWI Graz, Stremayrgasse 9, 8010 Graz, Austria.

ABSTRACT
Oxygen quantification in trace amounts is essential in many fields of science and technology. Optical oxygen sensors proved invaluable tools for oxygen measurements in a broad concentration range, but until now neither optical nor electrochemical oxygen sensors were able to quantify oxygen in the sub-nanomolar concentration range. Herein we present new optical oxygen-sensing materials with unmatched sensitivity. They rely on the combination of ultra-long decaying (several 100 ms lifetime) phosphorescent boron- and aluminium-chelates, and highly oxygen-permeable and chemically stable perfluorinated polymers. The sensitivity of the new sensors is improved up to 20-fold compared with state-of-the-art analogues. The limits of detection are as low as 5 p.p.b., volume in gas phase under atmospheric pressure or 7 pM in solution. The sensors enable completely new applications for monitoring of oxygen in previously inaccessible concentration ranges.

No MeSH data available.


Related in: MedlinePlus

Synthesis of the borondifluoride chelates and aluminium complexes
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Related In: Results  -  Collection


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Figure 1: Synthesis of the borondifluoride chelates and aluminium complexes

Mentions: The new sensing materials rely on novel difluoroboron- and aluminium chelates of 9-hydroxyphenalenone (HPhN, Fig. 1) 21 and its benzannelated derivative 6-hydroxybenz[de]anthracene-7-on (HBAN, Fig. 1).22 In contrast to the common fluorescent difluoroboron chelates of dipyrromethenes and tetraarylazadipyrromethenes23,24 the new difluoroboron-based dyes simultaneously show prompt fluorescence, delayed fluorescence and phosphorescence when embedded in polymers (Fig. 2a, Fig. 2b). Room temperature phosphorescence is an extremely rare phenomenon for compounds with no heavy atoms. It was previously observed for BF2-chelates of aliphatic β-diketones coupled to polylactic acid16,17 or physically entrapped in the same polymer.19 This work and our results indicate that phosphorescence of aliphatic and aromatic BF2-chelates of β-diketones appears to be a general phenomenon. As can be seen, the extension of π-conjugation in 9-hydroxyphenalenone derivatives results in bathochromic shifts of absorption, fluorescence and phosphorescence compared to the reported aliphatic diketonate chelates. In fact, the absorption of the HPhN and HBAN difluoroboron chelates peaks at 450 nm and 459 nm, respectively, (ε450 = 10.2×103 M−1 cm−1 and ε459 = 12.9×103 M−1 cm−1). This enables excitation with bright blue 450 nm and 470 nm LEDs and with conventional white light sources. Temperature affects the quantum yields of all three emissions. As expected, the phosphorescence QYs decrease at higher temperature and the delayed fluorescence becomes stronger (Fig. 2b). Since both phosphorescence and delayed fluorescence possess virtually identical decay times (Supplementary Fig. 1) and are quenched by oxygen to the same extent, their ratio can be used to eliminate temperature crosstalk. Importantly, prompt fluorescence is suitable for referencing purposes, as it is not affected by oxygen. However, the most outstanding property of these dyes is their extraordinary long phosphorescence decay time of 360 and 730 ms for BF2(HPhN) and BF2(HBAN), respectively (in polystyrene at 20°C), which, to the best of our knowledge, are the longest decay times recorded for visible light excitable dyes. This is likely due to the rigid aromatic backbone structure of the dyes. Despite those long decay times, the phosphorescence quantum yields are fairly high (Table 1, Supplementary Table 1).


Ultra-sensitive optical oxygen sensors for characterization of nearly anoxic systems.

Lehner P, Staudinger C, Borisov SM, Klimant I - Nat Commun (2014)

Synthesis of the borondifluoride chelates and aluminium complexes
© Copyright Policy
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC4109599&req=5

Figure 1: Synthesis of the borondifluoride chelates and aluminium complexes
Mentions: The new sensing materials rely on novel difluoroboron- and aluminium chelates of 9-hydroxyphenalenone (HPhN, Fig. 1) 21 and its benzannelated derivative 6-hydroxybenz[de]anthracene-7-on (HBAN, Fig. 1).22 In contrast to the common fluorescent difluoroboron chelates of dipyrromethenes and tetraarylazadipyrromethenes23,24 the new difluoroboron-based dyes simultaneously show prompt fluorescence, delayed fluorescence and phosphorescence when embedded in polymers (Fig. 2a, Fig. 2b). Room temperature phosphorescence is an extremely rare phenomenon for compounds with no heavy atoms. It was previously observed for BF2-chelates of aliphatic β-diketones coupled to polylactic acid16,17 or physically entrapped in the same polymer.19 This work and our results indicate that phosphorescence of aliphatic and aromatic BF2-chelates of β-diketones appears to be a general phenomenon. As can be seen, the extension of π-conjugation in 9-hydroxyphenalenone derivatives results in bathochromic shifts of absorption, fluorescence and phosphorescence compared to the reported aliphatic diketonate chelates. In fact, the absorption of the HPhN and HBAN difluoroboron chelates peaks at 450 nm and 459 nm, respectively, (ε450 = 10.2×103 M−1 cm−1 and ε459 = 12.9×103 M−1 cm−1). This enables excitation with bright blue 450 nm and 470 nm LEDs and with conventional white light sources. Temperature affects the quantum yields of all three emissions. As expected, the phosphorescence QYs decrease at higher temperature and the delayed fluorescence becomes stronger (Fig. 2b). Since both phosphorescence and delayed fluorescence possess virtually identical decay times (Supplementary Fig. 1) and are quenched by oxygen to the same extent, their ratio can be used to eliminate temperature crosstalk. Importantly, prompt fluorescence is suitable for referencing purposes, as it is not affected by oxygen. However, the most outstanding property of these dyes is their extraordinary long phosphorescence decay time of 360 and 730 ms for BF2(HPhN) and BF2(HBAN), respectively (in polystyrene at 20°C), which, to the best of our knowledge, are the longest decay times recorded for visible light excitable dyes. This is likely due to the rigid aromatic backbone structure of the dyes. Despite those long decay times, the phosphorescence quantum yields are fairly high (Table 1, Supplementary Table 1).

Bottom Line: The sensitivity of the new sensors is improved up to 20-fold compared with state-of-the-art analogues.The limits of detection are as low as 5 p.p.b., volume in gas phase under atmospheric pressure or 7 pM in solution.The sensors enable completely new applications for monitoring of oxygen in previously inaccessible concentration ranges.

View Article: PubMed Central - PubMed

Affiliation: Institute of Analytical Chemistry and Food Chemistry, Graz University of Technology, NAWI Graz, Stremayrgasse 9, 8010 Graz, Austria.

ABSTRACT
Oxygen quantification in trace amounts is essential in many fields of science and technology. Optical oxygen sensors proved invaluable tools for oxygen measurements in a broad concentration range, but until now neither optical nor electrochemical oxygen sensors were able to quantify oxygen in the sub-nanomolar concentration range. Herein we present new optical oxygen-sensing materials with unmatched sensitivity. They rely on the combination of ultra-long decaying (several 100 ms lifetime) phosphorescent boron- and aluminium-chelates, and highly oxygen-permeable and chemically stable perfluorinated polymers. The sensitivity of the new sensors is improved up to 20-fold compared with state-of-the-art analogues. The limits of detection are as low as 5 p.p.b., volume in gas phase under atmospheric pressure or 7 pM in solution. The sensors enable completely new applications for monitoring of oxygen in previously inaccessible concentration ranges.

No MeSH data available.


Related in: MedlinePlus