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.
Highlights
Since its discovery, the single-walled carbon nanotube (SWNT) has been intensively studied by researchers due to its special electrical and physical characteristics
The AC source applied across the electrodes generates a non-uniform electric field, which causes the electrons and protons in the SWNTs to move away from their balanced positions
The electric field exerts dielectrophoretic forces on the SWNTs and forces them to rotate along the field lines
Summary
The single-walled carbon nanotube (SWNT) has been intensively studied by researchers due to its special electrical and physical characteristics. Bioelectronic chips based on SWNTs and field-effect transistors (FETs) have been developed by a number of groups; they have demonstrated high performance as biosensors [14,15,16] Many of these sensors rely on the accurate and real-time detection of pH value which is one of the most critical measurable parameters in many fields such as medicine, chemistry, biology, material science, etc. Dielectrophoresis, a simple but versatile method, has proven to be effective in organizing single-walled carbon nanotubes (SWNTs) in small and large scales, resulting in devices with predictable properties and performance [19,20]. This method can be conducted at room temperature with low voltages. The sensing repeatability across multiple sensors, the response time, and the stability of the sensor over time are described and discussed in this paper
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
