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

ZnO Transducers for Photoluminescence-Based Biosensors: A Review

“…Table 1 summarizes some of the most relevant works reported so far in the literature concerning the use of the ZnO PL signal in immunosensors. At this point, we would like to highlight that even though most of the works devoted to the use of ZnO nanostructures in biosensing research use phosphate-based buffer solutions, a recent study by our group pointed out the fact that ZnO conversion into zinc phosphate takes place when in contact with phosphate ions, even at the physiological pH [104]. A detailed discussion on this topic is presented in Section 4 of this paper.…”

“…Phosphate-based buffers are widely used in biosensing experiments to keep a constant pH, as well as an ion concentration that mimics the human blood [139]. However, it was seen that when ZnO micro/nanostructures are in contact with solutions containing phosphate ions, the ZnO structures suffer a phase conversion toward zinc phosphate [104,140,141], which significantly affected their transduction signal, particularly in the case of the PL output. As such, errors may be induced in the analysis of the transducing results, hampering the utilization of this semiconductor as a transducer if such phenomena are not well understood.…”

“…As such, errors may be induced in the analysis of the transducing results, hampering the utilization of this semiconductor as a transducer if such phenomena are not well understood. Hence, a systematic study to understand these effects was conducted and the detailed analysis of the obtained results can be seen in [104].…”

“…On one hand, in the case of pH 7.4, besides the initial ZnO tetrapods, randomly distributed spherical-like shaped particles with diameters around 500 nm were also detected, evidencing some agglomerates mixed with the tetrapodal structures, which continue to be abundantly present. According to the Raman spectroscopy and X-ray diffraction (XRD) structural data, these particles are mostly amorphous, although traces of crystalline phases were also identified [104]. On the other hand, for the structures immersed in the solution with pH 5.8 during the same time, profound changes took place.…”

“…These structures exhibited higher dimensions, in the range of tens to a few hundred µm and seemed to grow radially from a common center, being organized in a hierarchical branched structure. The newly formed crystal displays a parallelepiped shape with well-defined facets, presenting widths below 1 µm and lengths with tens of µm (Figure 12) [104].…”