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Dielectrophoresis Aligned Single-Walled Carbon Nanotubes as pH Sensors.

Li P, Martin CM, Yeung KK, Xue W - Biosensors (Basel) (2011)

Bottom Line: The real-time data acquisition shows that the sensor response time depends on the pH value, ranging from 2.26 s for the pH-5 solution to 23.82 s for the pH-9 solution.The long-term stability tests illustrate that the sensors can maintain their original sensitivity for a long period of time.The simple fabrication process, high sensitivity, and fast response of the SWNT-based sensors facilitate their applications in a wide range of areas.

View Article: PubMed Central - PubMed

Affiliation: Mechanical Engineering, School of Engineering and Computer Science, Washington State University, 14204 NE Salmon Creek Avenue, Vancouver, WA 98686, USA. pengfei_li@wsu.edu.

ABSTRACT
Here we report the fabrication and characterization of pH sensors using aligned single-walled carbon nanotubes (SWNTs). The SWNTs are dispersed in deionized (DI) water after chemical functionalization and filtration. They are deposited and organized on silicon substrates with the dielectrophoresis process. Electrodes with "teeth"-like patterns-fabricated with photolithography and wet etching-are used to generate concentrated electric fields and strong dielectrophoretic forces for the SWNTs to deposit and align in desired locations. The device fabrication is inexpensive, solution-based, and conducted at room temperature. The devices are used as pH sensors with the electrodes as the testing pads and the dielectrophoretically captured SWNTs as the sensing elements. When exposed to aqueous solutions with various pH values, the SWNTs change their resistance accordingly. The SWNT-based sensors demonstrate a linear relationship between the sensor resistance and the pH values in the range of 5-9. The characterization of multiple sensors proves that their pH sensitivity is highly repeatable. The real-time data acquisition shows that the sensor response time depends on the pH value, ranging from 2.26 s for the pH-5 solution to 23.82 s for the pH-9 solution. The long-term stability tests illustrate that the sensors can maintain their original sensitivity for a long period of time. The simple fabrication process, high sensitivity, and fast response of the SWNT-based sensors facilitate their applications in a wide range of areas.

No MeSH data available.


Related in: MedlinePlus

(a) An SEM image of sparsely distributed SWNTs across the electrodes right after the dielectrophoresis deposition. (b) An SEM image of congregated SWNTs after the droplet placing and removing steps.
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biosensors-01-00023-f005: (a) An SEM image of sparsely distributed SWNTs across the electrodes right after the dielectrophoresis deposition. (b) An SEM image of congregated SWNTs after the droplet placing and removing steps.

Mentions: In our investigation, it is observed that the droplet placing and removing steps need to be performed a few times (10–15) before the sensor shows a stable response to pH solutions. We believe that during the first few instances of sensor wetting and drying, some SWNTs lose the connection with the electrodes and are washed away in the process. Therefore, only the initially strongly-bond SWNTs remain on the surface. The effect can be demonstrated by monitoring the SWNTs before and after the wetting and drying steps. Figure 5(a) shows the aligned SWNTs right after the dielectrophoresis process but before the pH sensing steps. The SWNTs are sparsely distributed and loosely connected to the electrodes. In comparison, Figure 5(b) shows the remaining SWNTs after a few instances of droplet placing and removing. The originally sparsely distributed SWNTs are now tightly congregated together and form a dense network. This is attributed to liquid surface tension when the solution residual evaporates. The surface tension pulls the SWNTs together and reinforces the connection between the SWNTs and the electrodes. In addition, the loosely-bond SWNTs are removed during the process. As a result, the sensor becomes more stable and demonstrates higher repeatability after these droplet placing and removing steps.


Dielectrophoresis Aligned Single-Walled Carbon Nanotubes as pH Sensors.

Li P, Martin CM, Yeung KK, Xue W - Biosensors (Basel) (2011)

(a) An SEM image of sparsely distributed SWNTs across the electrodes right after the dielectrophoresis deposition. (b) An SEM image of congregated SWNTs after the droplet placing and removing steps.
© Copyright Policy
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4264346&req=5

biosensors-01-00023-f005: (a) An SEM image of sparsely distributed SWNTs across the electrodes right after the dielectrophoresis deposition. (b) An SEM image of congregated SWNTs after the droplet placing and removing steps.
Mentions: In our investigation, it is observed that the droplet placing and removing steps need to be performed a few times (10–15) before the sensor shows a stable response to pH solutions. We believe that during the first few instances of sensor wetting and drying, some SWNTs lose the connection with the electrodes and are washed away in the process. Therefore, only the initially strongly-bond SWNTs remain on the surface. The effect can be demonstrated by monitoring the SWNTs before and after the wetting and drying steps. Figure 5(a) shows the aligned SWNTs right after the dielectrophoresis process but before the pH sensing steps. The SWNTs are sparsely distributed and loosely connected to the electrodes. In comparison, Figure 5(b) shows the remaining SWNTs after a few instances of droplet placing and removing. The originally sparsely distributed SWNTs are now tightly congregated together and form a dense network. This is attributed to liquid surface tension when the solution residual evaporates. The surface tension pulls the SWNTs together and reinforces the connection between the SWNTs and the electrodes. In addition, the loosely-bond SWNTs are removed during the process. As a result, the sensor becomes more stable and demonstrates higher repeatability after these droplet placing and removing steps.

Bottom Line: The real-time data acquisition shows that the sensor response time depends on the pH value, ranging from 2.26 s for the pH-5 solution to 23.82 s for the pH-9 solution.The long-term stability tests illustrate that the sensors can maintain their original sensitivity for a long period of time.The simple fabrication process, high sensitivity, and fast response of the SWNT-based sensors facilitate their applications in a wide range of areas.

View Article: PubMed Central - PubMed

Affiliation: Mechanical Engineering, School of Engineering and Computer Science, Washington State University, 14204 NE Salmon Creek Avenue, Vancouver, WA 98686, USA. pengfei_li@wsu.edu.

ABSTRACT
Here we report the fabrication and characterization of pH sensors using aligned single-walled carbon nanotubes (SWNTs). The SWNTs are dispersed in deionized (DI) water after chemical functionalization and filtration. They are deposited and organized on silicon substrates with the dielectrophoresis process. Electrodes with "teeth"-like patterns-fabricated with photolithography and wet etching-are used to generate concentrated electric fields and strong dielectrophoretic forces for the SWNTs to deposit and align in desired locations. The device fabrication is inexpensive, solution-based, and conducted at room temperature. The devices are used as pH sensors with the electrodes as the testing pads and the dielectrophoretically captured SWNTs as the sensing elements. When exposed to aqueous solutions with various pH values, the SWNTs change their resistance accordingly. The SWNT-based sensors demonstrate a linear relationship between the sensor resistance and the pH values in the range of 5-9. The characterization of multiple sensors proves that their pH sensitivity is highly repeatable. The real-time data acquisition shows that the sensor response time depends on the pH value, ranging from 2.26 s for the pH-5 solution to 23.82 s for the pH-9 solution. The long-term stability tests illustrate that the sensors can maintain their original sensitivity for a long period of time. The simple fabrication process, high sensitivity, and fast response of the SWNT-based sensors facilitate their applications in a wide range of areas.

No MeSH data available.


Related in: MedlinePlus