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42617-G10
Large-Scale Integration of Polymer Nanowires into Si Devices for Nanoelectronics and Nanosensor Arrays
The research supported by this grant was aimed at the development of a series conducting polymer/carbon nanotube composite structures for electronic and biosensor applications. Among conducting polymers, polyaniline is unique since it is environmentally stable and easy to fabricate. It has been applied widely in chemical sensors but not as much in biosensors. The reason is that native polyaniline is neither electrochemically active nor conductive in neutral solutions, which is a prerequisite for biosensor applications. It is also limited both in the variety of molecules that can be detected and in the selectivity of the detection. Last year, we reported that we fabricated poly (aniline boronic acid) (PABA)/carbon nanotube composites which successfully extended the electrochemical activity and conductivity of polyaniline to neutral pH solutions. This year, using this remarkable new material we developed an innovative non-oxidative electrochemical sensor for sensitive and selective detection of neurotransmitter dopamine. The challenge for detection of dopamine is that that the concentration of dopamine in the extracelluar fluid of the caudate nucleus in brains is extremely low (0.01-1µM) for a healthy individual and in the nanomolar range for patients with Parkinson's disease, while the concentrations of the main detection interferents, e.g., ascorbic acid, are several orders of magnitude higher and the interferents undergo oxidation within the same potential window as dopamine. We studied and eliminated the interference of ascorbic acids for practical applications. The high sensitivity and selectivity of the sensor show excellent promise toward molecular diagnosis of Parkinson's disease. Two papers are published along this line. One is in Anal. Chem. Another one is in J. Phys. Chem. B (Galley proof of the manuscript has been sent back to the publisher).
There is increasing enthusiasm for the use of single walled carbon nanotube (SWNT) networks as conductive flexible electrodes and sensing materials. However, all the experimentally measured conductivities of the SWNT networks are significantly lower than the conductivity of a SWNT rope (axial conductivity ~ 10 000 – 90 000 S/cm). Inspired by the remarkable (electronic, thermal conductivity and the superior mechanical) properties of carbon nanotubes (CNTs), tremendous efforts have been made over the past decade to prepare polymer and CNT composites with an aim to synergistically combine the merits of each individual component. However, most of the reported composites show enhancement over polymeric materials, but much lower performance compared to CNTs. Herein, we report the conductivity of the SWNT network can be dramatically improved by in-situ polymerization of a thin layer of self-doped conducting polymer around and along the carbon nanotubes. The formed conducting polymer improves the contacts between the SWNTs, it also acts as a “conductive glue” effectively assemble the SWNTs into a conductive network, which largely decreased the amount of SWNTs to reach the high conductive regime of the network. The conductance of the composite network after percolation threshold is two magnitudes higher than the network formed from SWNT alone. More importantly, the conducting polymer layer brings in powerful functionality for a variety of potential applications, including flexible sensors. The two manuscripts were submitted in 2007 for scientific publication.
Dispersions and functionalizations of SWNTs with different dispersing methods and dispersing agents result in SWNTs with different electronic structures and surface chemistries. Motivated by production of stable and high performance PABA/SWNT nanocomposites with lower cost, we extensively studied the impact of dispersion and functionalization of the carbon nanotubes on the molecular structure of the polymer, the arrangement and distribution of the carbon nanotubes in the composite, and consequently the electronic performance of the composites. This fundamental research provides important guidelines for production of conducting polymer/carbon nanotube composites in variety applications, especially for flexible electronics and sensors. Partially the results were published in three conference proceedings (NSTI Nanotech, the Nanotechnology conference and Trade Show, 2007 and Society of Photo-Optical Instrumentation Engineers (SPIE) 2007. The manuscripts are being documenting for scientific publication.
Through support from this grant the PI has been able to gather fundamentally new insight regarding the preparation of conducting polymer/carbon nanotube composite materials for electronics and biosensor applications. Moreover, numerous graduate and undergraduate students (including several minority students) were trained. The students were able to acquire skills in carbon nanotubes dispersion, composite fabrication and gain hands-on experience with a variety of characterization tools, such as scanning probe microscopy, electronic and electrochemicalcharaterization of the composite materials.
