For this research project highly sensitive Single wall carbon nano-tubules (SWNTs)are deposited by chemical vapor deposition (CVD) techniques on the surface of novel contour-mode AlN piezoelectric MEMS/NEMS resonators to form batteryless acoustic sensor wireless platforms for the detection of different gas species. A circuit will detect a particular species by finding differences between the resonant frequencies of micro/nanoresonators loaded with carbon nanotubes and decorated with inkjet deposited ss-DNA sequences. A high degree of specificity will result from the sequence dependent adhesion between the volatile organic molecules and the resonators. After a few seconds, the organic molecules will detach from the DNA enabling built-in reset as the environment changes. The RF interface electronics will periodically report these changes to an external interrogator. The resonant aluminum nitride (AlN) contour-mode sensor platform functionalized by combinations of single stranded DNA on single wall carbon nanotubes that is proposed here will permit several orders of magnitude enhancement of state-of-the-art sensor performance. Specifically, the new platform will make possible: (i) 10x reduction in the false alarm rate, (ii) 1,000x improvement in sensitivity (from part per billion to part per trillion thanks to extremely small resonant mass and high frequency of operation), (iii) 1,000x reduction in size for 100 analytes detection in a small volume, (iv) 200x power savings, (v) faster response time (< 5 seconds thanks to self-refreshing sensor), (vi) dramatically reduced fabrication costs (thanks to batch production), (vii) remote operations (resonator as RFID tag) and (viii) almost zero operating expenses (thanks to the disposable nature of the sensor).
This project enabled the development of a new class of wireless nanoscale gas sensing platforms. For the first time, carbon nanotubes (CNTs) and single-stranded DNA were integrated with surface micromachined active components that permit direct wireless interface of nanodevices with larger scale systems. Highly sensitive CNTs were deposited by catalytic chemical vapor deposition (CVD) techniques on the surface of piezoelectric MicroElectroMechanical Systems (MEMS) resonators to form acoustic sensor wireless platforms for the detection of gases such as methanol, trimethylamine, dinitrotoluene (DNT), and dimethylmethylphosphonate (sarin analog). The work lead to the realization of platforms of multiple-frequency and high-Q MEMS resonators on which analyte-specific CNTs are used as gas sensitive elements. High selectivity between different gases was provided by surface functionalization of the CNTs or of the resonators with single-stranded DNA. The resonant devices were configured in large arrays and interfaced with electronics to monitor their performance. The overall system offered unparalleled levels of sensitivity (from ppb to few ppt) and selectivity, fast response time, measurements reversibility, ability to wirelessly interface to the macroworld and reduced power consumption. In summary, the research efforts lead to the following main outcomes: (i) the development of micro/nano fabrication techniques for large scale co-fabrication of nanotubes with MEMS resonators; (ii) fundamental understanding of gas adsorption mechanisms at the nanoscale level; (iii) understanding of noise mechanism in mechanical resonators and their limit of detection for gas sensing applications; (iv) raising the frequency of operation and quality factor of piezoelectric microresonators; and (v) realizing a platform of arrays of micro/nanoscale resonators integrated with the required electronics for signal conditioning. This project had a broader impact at the level of both fundamental and applied sciences. At the fundamental science level, a deeper understanding of the chemi-sorption process of gases on surface functionalized CNTs and resonators emerged. At the applied level, a new resonant platform for gas sensing was developed. The novel system capable of interfacing ultra-sensitive nanostructures with larger scale systems will have a disruptive impact on gas sensors for bio-hazard detection, environmental monitoring and homeland security. The discoveries and technological progress made with this program will enable unprecedented levels of sensitivity to biological/chemical threats in a very small form factor. In addition, the development of multiple frequency resonant M/NEMS components will permit tremendous advancements in the area of wireless communications. The discoveries under this project resulted in new levels of understanding of nanoscale phenomena and systems that were used by the investigator in lecturing undergraduate and graduate courses in the area of nanoscience and nanotechnology. The outcomes of this scientific work were directly integrated in the courses taught by the investigator and impacted a broad group of students. Furthermore high school students (in SAAST), undergraduates (in SUNFEST), and high school teachers (in NBIC RET) were engaged in this program. The general public was made aware of the progress in this project through the activities sponsored by the NanoDay at the University of Pennsylvania. Finally, the research project benefitted the operation, maintenance and modernization of the microfabrication facility at the University of Pennsylvania, a shared infrastructure used for research and educational purposes in the areas of micro and nanotechnologies.
