Jessica R. Cooper

Volatile organic compound discrimination using nanostructured polythiophene sensors

New synthesis methods have allowed us to make many semiconducting polythiophenes polymers with different side and end groups. Also, co-polymers combining a polythiophene chain attached to another polymer chain were synthesized. This design freedom brings a new dimensionality to the sensing properties of the materials. Single chip micro sensor resistor arrays, utilizing multiple polymers, were fabricated and then tested in an automated system. The sensors demonstrated ppm level sensitivity to various volatile organic compounds (VOCs) including both polar and non-polar materials. Polymers with different chemical structures show strong selectivity to different VOCs. By applying pattern recognition algorithms, the sensor response clearly discriminates between the tested VOCs allowing us to conjecture as to the role molecular modification have in determining response to specific VOCs

A CMOS MEMS Gold Plated Electrode Array for Chemical Vapor Detection

This work presents the fabrication and demonstration of an electroless gold plated CMOS-MEMS chemresistor array sensor for selective detection of volatile organic compounds, with conductive polythiophene polymer used as an active sensing material. Chemresistor electrode fabrication involves post-CMOS etching and electroless plating steps. An electroless gold plating process selectively deposits gold onto the CMOS aluminum electrodes to provide ohmic contact to the polymer layer. Electroless gold techniques are optimized to provide for a sub-micron vertical gap between the chemresistor electrodes. Polymer solutions are then deposited onto electrodes using drop-on-demand inkjet printing. Measured device response to methanol, acetone, and acetonitrile vapors demonstrates feasibility.

Nanostructure Dependence of Conductive Polymer Chemical Sensors

It is shown that the resistive sensing properties of conductive polymers are highly dependent on the material nanostructure. The sensing properties of regioregular poly(3-hexylthiophene) (P3HT) polymer thin films with porous nanofibrile structure, dense nanofibrile structure and nano-granular structure show very different conductance changes, in terms of both response amplitude and sign, upon exposure to various VOC vapors. This implies that multiple sensing mechanisms, such as both grain boundary and intra-grain effects, exist and the dominant sensing mechanism can vary with different material nanostructures. Possible mechanisms for these effects, and their correlation with observed material nanostructures, are also discussed.

Regioregular polythiophene nanowires and sensors

We have developed and synthesized highly conductive regioregular poly(3-alkylthiophene) (rr-PAT) derivatives for use in sensor arrays on a chip. Poly(3-alkylthiophene)s are ideally suited for this application because of their excellent electrical properties, solution processability and our ability to modify their chemical structure. Here, we synthesized rr-PATs that have different side chains and different end groups. The polymers were ink-jetted onto ChemFET devices on a chip and their chemical sensing properties were tested to a variety of volatile organic compounds (VOCs). The sensors demonstrated ppm level sensitivity and selectivity to all VOCs tested, including both polar and non-polar compounds.