Functionalisation of inkjet-printed Organic Field Effect Transistors with odorant binding proteins for the detection of gaseous analytes

Inkjet-printing of solution-processable organic materials is a well-known fabrication method utilised to produce electronic devices on flexible substrates. It is especially suitable to realise, with a simple, digital layout design process, large-area devices with limited production costs [1]. Among the several different types of electronic devices already fabricated, a particularly important role is played by Organic Field Effect Transistors (OFETs) [2]. OFETs have been already proved to be capable to detect chemical or biological analytes in gaseous environments [3, 4], essentially by exploiting the chemo-physical interaction between the gaseous species to be detected and the transistor’s semiconductive channel, but so far the integration of biological molecules into the transistors’ active layers to improve sensing performances has received little attention. In addition to that, it should be also pointed out the fact that, in most cases, gas-sensing OFETs reported in the literature were fabricated with expensive cleanroom fabrication techniques on rigid substrates. In this paper, we address these two different issues. First of all, we report on the fabrication of bottom-contact, top-gate OFETs on flexible, plastic substrates (PEN) realised by means of inkjet-printing. Conductive layers and electrodes were fabricated by utilising inkjet-printable silver nanoparticles based inks while commercial inkjet-printable TIPS-pentacene and N2200 were used as active layers for the realisation of p – type and n – type channel organic transistors, respectively; parylene-C was used as gate dielectric while the gate electrode was fabricated by using a conductive polymer solution. The printed OFETs structure is shown in Fig. 1. In order to detect gaseous analytes, we opted for a different approach than that usually reported in the literature, choosing to functionalise the gate electrode by inserting, into the solution used for its fabrication, a small amount of odorant binding proteins (OBPs). This approach is compatible with roll-to-roll, large area production techniques and, in combination with the top-gate architecture, allows to maximise the sensing active area. OBPs are low-molecular-weight biological molecules highly concentrated in the nasal mucus of vertebrates and in the sensillar lymph of insects; their strong chemical affinity towards odours and pheromones suggests that they may play a crucial role in olfactory perception [5]. By incorporating OBPs within the gate electrode, we attempted to use such functionalised OFETs as transducers, in order to detect some typologies of Volatile Organic Compounds (VOC) (in particular, menthone and linalool); an example of OFET’s response to such menthone (in terms of current increase when the transistor is exposed to the analyte plotted as a function of gate voltage) is depicted in Fig. 2. The preliminary results obtained, prove that OBPs may be successfully used to functionalise OFETs in order to make organic transistors able to detect VOCs.