Contatto di riferimento: Laura Basiricò
Partecipanti: Isacco Gualandi
Organic Electrochemical Transistors (OECTs) have been proposed as low cost chemical sensors for several analytes thanks to their remarkable features such as signal amplification, the use of an easy and cheap readout electronics and the feasibility on miniaturization. An OECT is composed by a stripe of conductive
polymer that works as a channel and by another electrode, usually a metal, that works as a gate.
When the device is dipped in an electrolyte solution, the current flowing in the channel can be modulated through the gate voltage because it promotes electrochemical reactions that change the charge carrier concentration in the polymer and, consequently, its conductivity.
Redox compounds can act on such processes by varying the doping degree of the conductive polymer, thereby changing the current density inside the channel.
This contribution describes the use of OECTs as chemical sensors for detecting redox-active compounds.
The OECT is based only on poly(ethylenedioxythiophene) poly(styrenesulfonate) (PEDOT:PSS) as conductive material. Firstly, the device was electrically characterized while the doping degree of the PEDOT:PSS in the channel was varying. These experiments show that the variation of the drain current (Id) is strongly related
to the concentration of charge carriers.
The OECT sensor was developed using ascorbic acid (vitamin C) as target compound. Ascorbic acid reacts with PEDOT:PSS by extracting charge carriers, so an increase of its concentration leads to a decrease of the absolute value of the current that flows in the channel. Id linearly depends on the logarithm of ascorbic acid concentration in the range 10-6 and 10-3 M. When the device is used in the optimized conditions, it shows a limit of detection equal to 10-8 M and a sensitivity of 4.5 ± 0.1 10-6 A decade-1.
The device can detect several compounds such as dopamine, adrenaline and gallic acid, suggesting a low selectivity. In order to overcome this weak spot, the OECT is being used for determining the total polyphenol content in wines, a useful index for evaluating the nutritional quality of food.