The impact of physiological buffer solutions on zinc oxide nanostructures: zinc phosphate conversion

• Published in: Materials today chemistry 2022-03, Vol.23, p.100629, Article 100629
• Main Authors: Rodrigues, J., Pereira, S.O., Zanoni, J., Falcão, B.P., Santos, N.F., Moura, J.P., Soares, M.R., Rino, L., Costa, F.M., Monteiro, T.
• Format: Article
• Language: English
• Subjects: Biosensors; Phase conversion; Phosphate ions; Photoluminescence; ZnO
• ISSN: 2468-5194; 2468-5194
• DOI: 10.1016/j.mtchem.2021.100629

Zinc oxide (ZnO) nanostructures have been widely used in biosensor applications. However, little attention has been given to the interaction of ZnO structures with physiological buffer solutions. In the present work, it is shown that the use of buffers containing phosphate ions leads to the modification of the ZnO tetrapodal micro/nanostructures when immersed in such solutions for several hours, even at the physiological pH (7.4). ZnO samples designed to be used as transducers in biosensors were immersed in phosphate buffers for several durations at pH = 5.8 and pH = 7.4. Their detailed morphological, structural and optical characterization was carried out to demonstrate the effect of the ZnO interaction with the phosphate ions. The pH had an important role in the ZnO conversion into zinc phosphate, with lower pH promoting a more pronounced effect. After 72 h and at pH = 5.8, a significant amount of the ZnO structures were converted into crystalline zinc phosphate, while immersion during the same time at pH = 7.4 resulted predominantly in amorphous zinc phosphate particles mixed with the original ZnO tetrapods. Photoluminescence spectra show remarkable changes with prolonged immersion times, particularly when the luminescence of the sample was investigated at 14 K. These findings highlight the importance of a careful analysis of the sensing results when phosphate-based buffer solutions are in contact with the ZnO transducers, as the changes observed on the transduction signal during sensing experiments may also comprise a non-negligible contribution from a phosphate-induced transformation of ZnO, which can hamper an accurate assessment of the sensing behavior. [Display omitted] •ZnO) structures are converted into crystalline zinc phosphate when immersed in phosphate-containing buffer solutions.•Level of pH and immersion time play key roles in the ZnO conversion.•Lower pH promotes a faster conversion of ZnO into zinc phosphate (Zn3(PO4)2).•The luminescence of these materials provides a simple and direct assessment of the phase/chemical conversion.•Phosphate-containing buffer solutions should be avoided when in contact with ZnO.