PRINTABLE CHEMICAL SENSORS BASED ON ORGANIC FIELD EFFECT TRANSISTORS

Abstract

The research examines the emerging role of organic field effect transistors (OFETs) in monitoring vaporous ammonia and n-alkyl amines. OFETs have been widely considered to be a promising tool for the detection of volatile organic compounds (VOCs) due to their ease of fabrication, flexibility and chemical functionality. This work investigates OFETs responses to alkyl amines (triethylamine, trimethylamine, n-butylamine, dibutylamine, and propylamine) detection by using low voltage solution processed bottom gate bottom contact (BGBC) OFETs. Air stable OFETs devices that can operate at low voltages (VGS = VDS = -3V) were fabricated using the solution processable polymer DPPTTT as a sensing layer. Both high-k and low-k dielectrics based on the ferroelectric polymer P(VDF-TrFE-CFE) and the PMMA cross-linked with benzophenone were used as a dielectric layer. For the detection of low concentrations of alkyl derivatives of ammonia critical parameters such as sensitivity, limit of detection and stability need to be predicted and potential interferences must eliminated. For this reason, ammonia detection was performed in the presence of humidity (RH=0-80%) in an attempt to elucidate the sensing mechanism. In addition, we examine the responses of OFETs to ammonia with potential interferences of detection by ethanol, acetone, esters. The results suggest a strong interference of VOCs with the active channel which can be attributed to the synergistic effect of dispersion, polar and hydrogen bond forces. Gas sensing results show that the sensitivity of the OFET sensor towards ammonia vapour over a concentration range between 2.5-14 ppb was 0.82-0.3 % ppb^-1 with LOD=2.20+-0.20 ppb. The dynamic region for ammonia vapour detection ranges from 2.20 ppb to 880 ppm. This is a remarkable result since the DPPTTT chemical sensor shows low detection limit and wide dynamic range. In the case of trimethylamine, triethylamine, n-butylamine, dibutylamine and propylamine vapours the magnitude of sensitive was 0.145+-0.008, 0.015+-0.00045, 1.18+-0.01, 10+-0.2, and 0.0180+-0.0005 %ppb^-1 respectively. These results are likely to be related to the heat of vaporisation at the boiling and the Antoine's C constant (AntC) of each analyte. The presence of VOCs alters the response to recovery rate ratio dramatically for both ammonia and n-alkyl amines. Sensors were exposed to analytes for varying lengths of time (1-12 min) to determine the optimum response characteristics. This work contributes to existing knowledge of analytical chemistry by providing innovative, inexpensive technology for monitoring vaporous ammonia derivatives with potential applications in food industry, environmental monitoring, and health care.

Date of Award	31 Dec 2021
Original language	English
Awarding Institution	The University of Manchester
Supervisor	Krishna Persaud (Supervisor) & Michael Turner (Supervisor)