Rapid and accurate methods allowing for detection of trace level of uranyl ion can be employed for environmental, geochemical or health safety applications. According to literature, at certain pH values uranyl has a strong affinity to phosphate residues. This mechanism was used in various electrochemical sensors for uranyl ion determination, with the recognition layer composed of: 2-mercatpoethanol/POCl₃, cysteamine/ 2-aminoethyl dihydrogen phosphate or (t-butylphenyl)-N,N-di-(isobutyl) carbamoylmethylphosphineoxide [1-3]. The uranyl ion detection limit for the last of above-mentioned sensor is at parts per million level. Nevertheless, the analytical procedure in this case was very complicated.

It was recently found out in our laboratory that recognition layer of short DNA oligonucleotides, formed on gold electrode, can be very useful for electrochemical uranyl detection. After subjection to sample solution containing uranyl ion (UO₂²⁺), the electrochemical properties of DNA layer changes. This can be quantified using an electrochemical marker (e.g. methylene blue). This approach allows for trace level determination of uranyl ion. Moreover, impedance spectroscopy can be employed to further lower the detection limit.

To evaluate the influence of pH on DNA-uranyl interactions, the Quartz Crystal Microbalance (QCM) measurements were conducted. The gold transducer was modified with single stranded DNA and subsequently subjected to uranyl solutions of different pH values. The decrease in transducer oscillation frequency corresponds to interactions of uranyl ions with ssDNA phosphate residues. The strongest DNA-uranyl interaction was observed at pH 5.0.

It is well known that uranyl has cleaving effect on DNA strands [4,5]. However, we did not noticed this during QCM tests. To further explore this problem, capillary electrophoresis experiments were performed. No degradation of oligonucleotide upon prolonged contact with uranyl ion solution was observed, thus it was concluded that proposed recognition monolayer can be utilized for preparation of uranyl ion sensors.

ACKNOWLEDGMENT

This work was co-financed by the Polish Ministry of Science and Higher Education (research project N N204 125237) and Warsaw University of Technology.

[1]    A. Becker, H. Tobias, D. Mandler, Anal. Chem. 2009, 81, 8627.

[2]    R. Banerjeea, Y. Katsenovichb, L. Lagosb, M. Sennc, M. Najad, V. Balsamoe, K. H. Pannellc, Ch. Li, Electrochim. Acta. 2010, 55, 7897

[3]    R. K. Shervedani, S. A. Mozaffari, Surf. Coat. Tech. 2005, 198, 123

[4]    P. E. Nielsen, C. Jeppesen, O. Buchardt, Febs Lett. 1988, 235, 122

[5]    M. Yazzie, Sh. L. Gamble, E. R. Civitello, D. M. Stearns, Chem. Res. Toxicol. 2003, 16, 524

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