Textile bioelectronic sensor: stability and selectivity

Abstract

Internet of Things (IoT) technology found application in many life aspects. Between IoT sensing layer possibilities, the Organic Electrochemical Transistors (OECTs), obtained with the p-conductive polymer PEDOT:PSS, showed stability, simplicity and low operation voltages. They can detect cation concentration variation into aqueous media. IMEM-CNR has extended the applicability of these devices by integration on textile fibers (tx-OECT). This conductive fiber is biocompatible, simple to obtain and absorbs the electrolyte spontaneously. This enables smart textile applications for analyte sensing in physiological fluids, as the human sweat. In addition, this group has been integrated this textile fiber directly into the plant's stem to obtain a device called Bioristor. This Bioristor can collect in vivo physiological data from plants during their life cycle and potentially be used in precision farming to reduce the environmental impact of the yield crops. The tx-OECT development focused on three aspects: i) in vitro and in vivo stability during the analysis, ii) sensitivity and selectivity towards biological molecules, such as proline, and iii) the selectivity towards specific cations, such as Ca(II). The stability study of textile OECT focused on two different PEDOT: PSS treatments: by introducing Ethylene glycol (EG) in the PEDOT:PSS formulation or by bathing the fiber with sulphuric acid (SA). Devices showed a non-linear degradation due to the PEDOT:PSS detachment from the gate fiber. The reduction of the applied gate voltage exponentially increased the device's stability. The best device performance (stability>30days) was obtained by using SA treated textile and applying 0.5V gate voltage. This protocol was tested in an open field tomato experiment. Devices were stable during the entire experiment. It was confirmed the capability of the bioristor to give an early warning of drought stress. Finally, by comparing bioristor signals with fruit production, it was concluded the 38% of irrigation water could be saved during the whole season. The proline selectivity and sensitivity were explored by mixing its molecularly imprinted polymer (MIP) with PEDOT:PSS to obtain the channel of the OECT. First experiments on planar devices showed sensitivity and selectivity to proline. Moreover, the OECT sensitivity to proline i) depended on the MIP concentration in the channel and ii) started in submicromolar concentration, even with proline mixed with 10mM Na(I) salt solution. Finally, the Ca(II) selectivity study focused on depositing an ion-selective membrane (ISM) on the fiber channel. The study focused on two different deposition methods: i) by dipping the channel into the membrane solution and, then, in a Ca(II) solution and ii) with a pre immersion in high Na(I) salt concentration followed by ISM deposition. The work showed that the second method is more affordable to obtain a selective device.