New Luminescent Europium Complexes as Indicators and in Sensors for pH in Biosamples and Water Samples

Wafaa Waleed Nafea Al-Qaysi
2018
The aim of my work was to design new low-cost optical luminescent pH sensor membranes and a sensor microtiterplate containing lanthanide complexes for continuous quantitation of pH over a wide range. These sensors should overcome the typical drawbacks of classical optical indicator dyes with a dynamic range of up to 3 pH units only (due to the mass action law) and of electrochemical sensors which cannot be miniaturized to µm-size or enable imaging over larger areas (e.g. in cell culture). We
more » ... refore introduced a new design concept for wide-range pH indicators and sensors that employs lanthanide complexes with ligands that have various pKas. Hence, a wider pH range becomes accessible. First, we complexed europium with three different ligands with various pKas to form an indicator. These ligands are Gallic acid (Gall) a trihydroxybenzoic type of phenolic acid that can strongly coordinate to Eu3+ ions via the carboxylic acid groups and has pKa1 = 4.5 and pKa2 = 10. Pyridine-2,6-dicarboxylic acid (PDA) is the second ligand that has pKa1 = 2.16 and pKa2 = 2.8. 2-Thenoyl trifloroacetone (TTA) with a pKa of 5.61 is the third ligand that is coordinated to Eu3+ ions. TTA is captures excitation light and efficiently transfers it to Eu3+ inducing a strong luminescence. We found that the Eu-TTA-PDA-Gall complex in a feed ratio (1:3:1:1) in aqueous buffer delivers a high luminescence emission that is dependent on pH over up to 8 orders of magnitude from pH 2–10 in aqueous solution. This is a unique pH response for a single indicator molecule. It was therefore embedded into a suitable polymeric membrane made from cellulose acetate (CA) in DMF in order to obtain pH sensor membranes. We found a reversible response of the emission intensity of the sensor membranes over a wide range of pH 2-pH 7 over 5 orders of magnitude within several minutes. Moreover, the first high-throughput pH sensor microtiterplate based on this indicator showed a dynamic range from pH 2–8 over 6 orders of magnitude and is suitable for up to 24 h of cont [...]
doi:10.5283/epub.38035 fatcat:25zkndhyofdunmtshb3k3o3rae