A label-free, organic transistor-based biosensor by introducing electric bias during DNA immobilization

We report an improved label-free DNA sensor based on pentacene organic thin-film transistors (OTFTs). OTFT with top-contact structure was first fabricated by using pentacene as the active layer. Different electric biases were introduced between the source and gate contacts of OTFT during the single-stranded DNA (ssDNA) immobilization process in order to improve the immobilization efficiency of DNA molecules on the pentacene substrate. Atomic force microscopy (AFM) images show the application of positive bias can significantly improve the amount of the immobilized ssDNA. The potentiostatic effect of bias can induce more ssDNA molecules onto the pentacene surface, which leads to the improvement of sensor sensitivity reflected by the electric signals of OTFTs. Furthermore, an optimized immobilization time of 30 min was obtained at a constant bias that exhibits the highest immobilization efficiency. With this design, the optimized process conditions (+50 V bias and an immobilization of 30 min) for the ssDNA immobilization on the pentacene film were also obtained. As a result, the introduction of bias during immobilizing ssDNA molecules has been proposed to improve the immobilized efficiency, which provides an effective path to enhance the sensitivity of OTFT-based DNA sensors. (C) 2012 Elsevier B.V. All rights reserved.