Stanford University MRSEC 0213618 IRG 3

1. Low-cost, reliable sensors will be achieved using devices capable of converting an analyte binding event to an easily read electrical signal. Organic thin-film transistors (OTFTs) are ideal for inexpensive, single-use chemical or biological sensors due to their compatibility with flexible, large-area substrates, simple processing, and highly tunable active layer materials. Chemical detection with OTFTs has been limited to vapors due to high operating voltage requirements and poor stability of the organic semiconductor. Low-operating voltage OTFTs were achieved using a thin, cross-linked polymer gate dielectric developed in collaboration between Bao and Knoll. Using the p-channel semiconductor 5,5’-bis-(7-dodecyl-9H-fluoren-2-yl)-2,2’-bithiophene (DDFTTF) as the active layer, high performance OTFTs were fabricated and displayed stable operation under aqueous conditions over more than 104 electrical cycles. The influence of water on the transistor characteristics is shown in Figure 1 below. These OTFTs could be used to monitor solution pH due to the strong influence of hydronium ions on the drain current. OTFT chemical sensors were demonstrated in aqueous solutions with concentrations as low as parts per billion for a variety of chemicals, including trinitrobenzene, methylphosphonic acid, cysteine and glucose. The sensitivity to a few notable chemicals is illustrated in Figure 2. Specific chemical and biological detection is currently in progress using plasma polymer and other OTFT modification methods. Sensors OTFT Chemical Curtis W. Frank, Stanford University, DMR 0213618 Fig.1 Image of flexible OTFT sensor and low-voltage OTFT operation and stability in water a Fig.2 Sub-ppm level chemical detection in aqueous solution with un-encapsulated OTFTs 10 μm 1 Stanford University MRSEC 0213618 IRG 3