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. 2009;9(11):8911-23.
doi: 10.3390/s91108911. Epub 2009 Nov 9.

Miniaturized pH Sensors Based on Zinc Oxide Nanotubes/Nanorods

Alimujiang Fulati  1 , Syed M Usman Ali, Muhammad Riaz, Gul Amin, Omer Nur, Magnus Willander
Affiliations

Miniaturized pH Sensors Based on Zinc Oxide Nanotubes/Nanorods

Alimujiang Fulati et al. Sensors (Basel). 2009.

Abstract

ZnO nanotubes and nanorods grown on gold thin film were used to create pH sensor devices. The developed ZnO nanotube and nanorod pH sensors display good reproducibility, repeatability and long-term stability and exhibit a pH-dependent electrochemical potential difference versus an Ag/AgCl reference electrode over a large dynamic pH range. We found the ZnO nanotubes provide sensitivity as high as twice that of the ZnO nanorods, which can be ascribed to the fact that small dimensional ZnO nanotubes have a higher level of surface and subsurface oxygen vacancies and provide a larger effective surface area with higher surface-to-volume ratio as compared to ZnO nanorods, thus affording the ZnO nanotube pH sensor a higher sensitivity. Experimental results indicate ZnO nanotubes can be used in pH sensor applications with improved performance. Moreover, the ZnO nanotube arrays may find potential application as a novel material for measurements of intracellular biochemical species within single living cells.

Keywords: ZnO nanorods; ZnO nanotubes; pH sensors; potentiometric measurements.

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Figures

Figure 1.
Figure 1.
(a) and (c) schematic diagram of ZnO nanorod and nanotube pH sensors, respectively; (b) and (d) SEM images of ZnO nanorods and nanotubes, respectively (insert in image (d) shows tilted cross sectional view of nanotubes. The scale bar is 1 μm).
Figure 2.
Figure 2.
SEM images of the initial experimental results measuring ZnO nanorods/nanotubes after exposure to buffer solutions with (a) pH = 2, (b) pH = 4, (c) pH = 7, (d) pH = 8, and (e) pH = 12 for ZnO nanorods, and (f) pH = 2, (g) pH = 4, (h) pH = 7, (i) pH = 8, and (j) pH = 12 for ZnO nanotubes (the insert SEM images are the same ZnO nanotubes before exposure to corresponding pH values.)
Figure 2.
Figure 2.
SEM images of the initial experimental results measuring ZnO nanorods/nanotubes after exposure to buffer solutions with (a) pH = 2, (b) pH = 4, (c) pH = 7, (d) pH = 8, and (e) pH = 12 for ZnO nanorods, and (f) pH = 2, (g) pH = 4, (h) pH = 7, (i) pH = 8, and (j) pH = 12 for ZnO nanotubes (the insert SEM images are the same ZnO nanotubes before exposure to corresponding pH values.)
Figure 3.
Figure 3.
Reproducibility test of the developed ZnO nanotube and nanorod pH sensors in buffer solution at pH 6.
Figure 4.
Figure 4.
(a) Repeatability test of five ZnO nanorod pH sensor electrodes at various pH buffer solutions. (b) Repeatability test of five ZnO nanotube pH sensor electrodes at various pH buffer solutions.
Figure 5.
Figure 5.
Experimental measurements of electrochemical potential vs pH comparison curves for ZnO nanorods and nanotubes immersed in (a) buffer and (b) CaCl2 solutions.
Figure 6.
Figure 6.
Schematic diagram showing the charge distribution at the metal oxide-electrolyte interface with surface charges in CaCl2 for (a) ZnO nanorods and (b) ZnO nanotubes.
See this image and copyright information in PMC

References

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