Organic thin film transistors as selective sensing platforms for Hg2+ ions and the amino acidcysteine

Abstract

In this short communication we report a sensor for divalent mercuric (Hg2+) ions that we constructed from a perylene bisimide (PBI)-based organic thin film transistor. We improved the performance of the n-channel device by positioning N,N′-dioctyl-3,4,9,10-perylenedicarboximide between the dielectric and the active layer (PBI), increasing the electron mobility (μ) from 0.002 to 0.25±0.04cm2V−1s−1 and enhancing the on/off ratio (Ion/Ioff) by two orders of magnitude (from 102 to 104). Based on a “thymine–Hg2+–thymine” mechanism and monitoring the shift in the threshold voltage (Vth), we used this transistor to discriminate Hg2+ ions from mixed ion solutions and it extended to different concentration Hg2+ solutions (from 50 to 350μM). By monitoring the shifts in drain current (IDS) and Vth, we also used this bilayer device as a sensor for cysteine, a thiol-containing amino acid; the selective detection of cysteine was accompanied by a red shift in the fluorescence maximum of PBI, from 532 to 537nm.