We demonstrate the ion-selective response of an electrolyte-gated carbon nanotube network based field-effect transistor fabricated on a flexible polyimide substrate. Selective response towards the two prominent second messengers for cellcell communication, namely K + and Ca 2+ is demonstrated by modifying the carbon nanotube network with different polymeric ion-selective membranes. The sensing mechanism relies on the transduction of the ionic signal in an electrical one due to an ionactivity dependent change of the membrane potential at the membrane/electrolyte interface, which leads to a change in the effective gate-potential affecting the charge transport in the semiconducting channel. These sensors can be successfully used to selectively detect concentrations of primary ions down to a concentration in the μM range even in solutions with a highly concentrated background of interfering ions. Our approach allows the realization of low-cost, flexible, portable and multipurpose biosensing devices.Index Terms-carbon nanotubes, electrolyte-gated field-effect transistor, flexible, ion-selective membrane, ion-sensitive fieldeffect transistor
A flexible enzymatic acetylcholinesterase biosensor based on an electrolyte-gated carbon nanotube field effect transistor is demonstrated. The enzyme immobilization is done on a planar gold gate electrode using 3-mercapto propionic acid as the linker molecule. The sensor showed good sensing capability as a sensor for the neurotransmitter acetylcholine, with a sensitivity of 5.7 μA/decade, and demonstrated excellent specificity when tested against interfering analytes present in the body. As the flexible sensor is supposed to suffer mechanical deformations, the endurance of the sensor was measured by putting it under extensive mechanical stress. The enzymatic activity was inhibited by more than 70% when the phosphate-buffered saline (PBS) buffer was spiked with 5 mg/mL malathion (an organophosphate) solution. The biosensor was successfully challenged with tap water and strawberry juice, demonstrating its usefulness as an analytical tool for organophosphate detection.
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