Sensors Organic Field-Effect Transistors used as Chemical Sensors

Typical Bottom Gate/Bottom Contacts configuration of an O-FET used as sensors (left, adapted from doi:10.1080/15583724.2013.808665) and parameters (Ids max., µlin. and H) varying under exposition to an analyte on a typical transfer curve.

The sensors studied are mainly organic field effect transistors (O-FETs) whose channel is an organic semiconductor.

Certain electrical characteristics of O-FETs vary when exposed to analytes and analysis of these variations can ideally lead to the type of analyte and its concentration. Examples of analyte-sensitive electrical characteristics are maximum drain-source current (Ids max.), charge-carrier mobility (µ) or hysteresis (H).

Thanks to STELORG, it is possible to design and synthesize organic semiconductor molecules that respond specifically to a type of analyte, thus considerably increasing the selectivity of the sensors. On the other hand, the instrumental development within the consortium also allows to increase the sensitivity of the sensors. The targeted application areas range from health (electronic nose to diagnose diseases) to the environment (leaks detection).

O-FET sensors for health applications

Relative response of different accessible electrical parameters as a function of concentration (in ppm) of ethanol or acetone. Adapted from dio: 10.1016/j.snb.2015.11.012.

 

The detection of acetone in breath is often a sign of developing diabetes. Selective detection of acetone with a low detectability limit is therefore an important health issue. Comparing the responses of different electrical characteristics (current, mobility and hysteresis) of an O-FET with a channel composed of P3HT (poly(3-hexylthiophene)) is an effective way to separate for example acetone and ethanol.

 

Mixed-signal instrumentation system developped for nomadic high voltages O-FETs measurements. Adapted from doi: 10.1109/ICECS.2016.7841194.

 

An adapted electronics to allow the nomadic characterization of ambipolar O-FETs under high voltages has been developed by colleagues specialized in mixed-signal instrumentation systems at ICube.

O-FET sensors for environmental applications

Ammonia (NH3) is considered as a possible carrier for hydrogen storage and transport, one of the channels for a decarbonized transport. However, NH3 remains a toxic gas, especially for humans, and the detection of possible leaks at low concentrations is crucial.

Use of ammonia for hydrogen storage and transport adapted from doi: 10.1021/acsenergylett.1c02189.

Chemical structure of PNDI-T2-Si4 adapted from doi: 10.1002/adfm.202007734

Recently, Lee et al. showed that some organic n-type semiconductors can form a stable anion radical in the presence of a strong Lewis base, such as NH3 (doi: 10.1021/acsami.6b14220). Following this principle, an n-type semiconductor (PNDI-T2-Si4) was specifically designed and synthesized by chemists of the STELORG consortium to be particularly selective to ammonia. In addition, the use of siloxane solubilizing chains results in a solid state arrangement that favors the sensitivity of the sensors which react to NH3 concentrations of the order of 10 ppm.

Other developments around the O-FET sensors

Specific bench with three different organic semiconductors deposited (blue, orange and purple) (left adapted from doi: 10.1038/s41598-021-88569-x). Optical lithography mask (center) and acquisition board and O-FETs gate (right) developed in STELORG.

A specific measurement bench is being developed in order to be able to deposit several organic semiconductors and thus to have several types of O-FETs channels simultaneously exposed to the same concentrations of the same analyte. This bench will allow to increase the selectivity of O-FETs sensors by increasing significantly the number of parameters to be exploited.

Representative publications of STELORG illustrating the results obtained in the field of sensors.

N. Kamatham, O.A. Ibraikulov, P. Durand, J. Wang, O. Boiron, B. Heinrich, T. Heiser, P. Lévêque, N. Leclerc and S. Méry, Adv. Funct. Mater.31 (2020) 2007734 DOI: 10.1002/adfm.202007734.

V. Frick, P. Lévêque, U. Soysal and T. Heiser, 2016 IEEE International Conference on Electronics, Circuits and Systems (ICECS) DOI: 10.1109/ICECS.2016.7841194.

P. Lienerth, S. Fall, P. Lévêque, U. Soysal and T. Heiser, Sensors and Actuators B225 (2016) 90 DOI:10.1016/j.snb.2015.11.012