ZnO conversion into zinc phosphate and its viability as transducer in optical biosensors

• Autor(a) principal: Yaacoub, Nicole Pereira
• Data de Publicação: 2022
• Tipo de documento: Dissertação
• Idioma: eng
• Título da fonte: Repositório Científico de Acesso Aberto de Portugal (Repositórios Cientìficos)
• Texto Completo: http://hdl.handle.net/10773/34523
• topic: ZnO; Zincphosphate; Phosphate-bufferedsaline (PBS); Photoluminescence (PL); Humanserumalbumin (HSA); Opticalbiosensors

In the manufacture of biosensing devices, various methods for the immobilization of biorecognition elements on the surface of the transducer material have been implemented, typically using phosphate containing solutions as phosphate-buffered saline (PBS) solution. In transducers composed of ZnO, contact with solutions such as PBS can result in its conversion into zinc phosphate and lead to changes in its properties. This conversion may lead to misinterpretations of the detection results if the transducer phase con- version is not taken into consideration during the sensing experiments. In this context, a study of the effects that may be take place on the ZnO surface by prolonged contact with PBS was carried out. To this end, ZnO nanostructures were produced, using the technique of laser-assisted flow deposition (LAFD), to compose the transducer element of the biosensor which was also modified with (3-aminopropyl)triethoxysilane (APTES), to infer about is role in the protection of the ZnO surface. Afterwards, the biosensors were immersed in two PBS solutions (pH=5.8 and pH=7.4) for 1, 3 and 6 days and the morphological, structural and optical properties were assessed. The photoluminescence (PL) studies revealed that, with increasing time of immersion in PBS, the ultraviolet (UV) emission suffered a shift to higher energies and an increase in its intensity, whereas the in- tensity of green luminescence (GL) decreased. Moreover, using scanning electron microscopy (SEM), several structural changes were also identified in the samples immersed for 6 days. The Raman and the Fourier-transform infrared spectroscopy (FTIR) spectra also presented new vibrational modes related to phosphate species in all the samples immersed after 1 day. These changes occurred regardless of the APTES modification. Furthermore, four sets of sensors were produced for the detection of human serum albumin (HSA). Sensing response was obtained for the sensors prepared with a ZnO transducer, functionalized and tested only using physiological solution (a buffer without phosphate species), as well as for sensors where commercial zinc phosphate was used as transducer (functionalization and testing carried out in PBS). In both cases, a decrease in the intensity of the UV emission was observed with increasing HSA concentration. For the sensors that used transducers of ZnO and ZnO immersed in PBS for 3 days (both function- alized and tested with PBS) the UV emission showed no specific tendency after the HSA incubations. Such behaviour was attributed to the presence of competitive phenomena occurring during the sensing experiments that may affect the intensity of the UV emission. Namely, continuous conversion into zinc phosphate due to the successive incubations in PBS and effective antigen-antibody interactions. Therefore, this study concluded that ZnO is not a reliable transducer for biosensing when phosphate-species are involved. However, the use of zinc phosphate may have some potential interests in this area, requiring more studies to assess this hypothesis.