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.
Highlights
ZnO is a promising material due to the wide direct band gap (3.37 eV) and large exciton binding energy (60 meV)
ZnO nanorods and nanowires for pH sensing and miniaturization of pH sensors have attracted considerable interest since the large surface-to-volume ratio leads to a short diffusion distance of the analyte towards the electrode surface, resulting in an improved signal-to-noise ratio, faster response times, enhanced analytical performance, and increased sensitivity [18,19]
We have reported the successful demonstration of the use of ZnO nanorods to measure the intracellular pH in human fat cells [20], which proves that ZnO nanostructures have unique biological advantages including non-toxicity, bio-safety, bio-compatibility and high electron communication features and make them one of the most promising materials for biosensor application
Summary
ZnO is a promising material due to the wide direct band gap (3.37 eV) and large exciton binding energy (60 meV). We have reported the successful demonstration of the use of ZnO nanorods to measure the intracellular pH in human fat cells [20], which proves that ZnO nanostructures have unique biological advantages including non-toxicity, bio-safety, bio-compatibility and high electron communication features and make them one of the most promising materials for biosensor application. There have been reports on the use of ZnO tubular structures as sensors with improved performance and higher sensitivity compared to ZnO nanorods and nanowires [21,22,23]. Our results show a linear response of the electrochemical potential of the developed pH sensor to various pH values and as high as twice the sensitivity of the ZnO nanorod pH sensor This shows the great potential in using ZnO nanotubes for pH sensing with improved performance
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