Random CNT network and regioregular poly(3-hexylthiophen) FETs for pH sensing applications: A comparison

BackgroundNowadays, there is a tremendous need for cheap disposable sensing devices for medical applications. Materials such as Carbon Nanotubes (CNTs) and regioregular P3HT are proven to offer a huge potential as cost-effective and solution processable semiconductors for (bio)sensing applications.MethodsCNT-based field-effect transistors (CNT-FETs) as well as regioregular P3HT-based ones (P3HT-FETs) are fabricated and operated in the so-called electrolyte-gated configuration. The active layer of the P3HT-FETs consists of a spin-coated regioregular P3HT layer, which serves on one hand as the active sensing element and on the other hand as passivation layer for the transistor's metal contacts. The active layer of the nanotube transistors consists of a randomly distributed single walled CNT-network (> 90% semiconducting tubes) deposited from a CNT-ink solution by spin-coating.ResultsWe compare both devices concerning their stability in aqueous environment and their response when exposed to buffers with different pH. We found that even if P3HT shows lower stability its pH sensitivity is reproducible even after long-term measurements.ConclusionCNT-FETs and P3HT-FETs offer different advantages and drawbacks concerning their stability in solution and the ease of fabrication. A discussion of their different sensing mechanisms as well as sensitivity is given here.General SignificanceThis work reports on fast and cost-effective production of solution processable thin-film transistors based on carbon nanotubes and regioregular P3HT and demonstrates their suitability as reliable pH sensors. This article is part of a Special Issue entitled Organic Bioelectronics — Novel Applications in Biomedicine.

► The performance of P3HT-FETs and CNT-FETs as pH sensors operated in an electrolyte gate mode was compared.
► The sensing mechanism was discussed for both devices.
► The stability in long-term measurements was discussed for both devices.