Development of naphthalene diimide-based n-type small-molecule organic mixed ionic-electronic conductor for the Organic electrochemical transistor
Creators: Kang, Seongdae
Publisher: name: University of Alberta Library
Year: 2024

<p>Organic semiconductors have become increasingly recognized for their inherent mechanical flexibility, tunable electronic properties, and solution processability. These offer an unprecedented advantage over their inorganic counterparts for the cost-effective and scalable manufacture of organic electronics. A market assessment in 2022 forecasts that the global biosensors market could reach 566 billion USD by 2030, reflecting an annual growth rate of 21.8% from 2023 to 2030. [1] This promising path of organic semiconductors, endowed with exceptional properties, promotes the advancement of cost-efficient and wearable organic electronics. Organic electrochemical transistors (OECTs) are promising platforms for bioelectronics due to their low operational voltages, use in aqueous environments, and signal amplification. Organic mixed ionic-electronic conductors (OMIECs), active channel materials for the OECTs, are recognized for their distinctive ionic and electronic transport properties. The development of OMIECs is crucial, setting the stage for the next wave of flexible, biocompatible, and energy-efficient organic electronic devices. <br>
In this study, the naphthalene diimide-based n-type small-molecule OMIEC, gNDI-Br2, is synthesized and utilized as an active channel in OECTs. The thin film morphology, microstructure, electrochemical properties, and OECT performance of the synthesized gNDI-Br2 are examined. Drop-casted gNDI-Br2 OECTs operate in accumulation mode, demonstrating a high transconductance of approximately 350 µS. The main advantage is that these devices are normally OFF, unlike the PEDOT:PSS OECTs. In the gNDI-Br2 solution concentrations, the spacing between photopatterned gold S/D electrodes was varied, and various annealing temperatures were explored. The aerosol-jet 3D printing (AJP) technique is utilized to fabricate the gNDI-Br2 OECT. The AJP method offers many benefits, including reduced material consumption, efficient processing, cost efficiency, high reproducibility, and adaptability during fabrication. The aerosol-jet printed gNDI-Br2 thin film exhibits improved morphology and microstructure, leading to an enhancement in the gNDI-Br2 OECT performance, achieving a transconductance of 1 mS. Furthermore, the capability to produce flexible n-type gNDI-Br2 OECTs using the AJP method highlights its potential in the realm of wearable OECT-based biosensors. <br>
By utilizing thiol self-assembled monolayers (SAMs) for gate electrode functionalization and the aerosol-jet printing technique, we present a disposable and flexible n-type SARS-CoV-2 OECT biosensor. With an antibody-functionalized gold gate electrode, the gNDI-Br2 OECT demonstrates a great selectivity of 15.95 ± 0.72 mV dec−1 towards wild-type SARS-CoV-2 spike proteins and 18.84 ± 0.85 mV dec−1 for the SARS-CoV-2 Omicron variants spike proteins, compared to the negligible sensitivity of 0.16 ± 0.28 mV dec−1 to the H1N1 HA protein. This aerosol-jet printed, flexible n-type gNDI-Br2 OECT biosensor offers a potential platform for creating a range of low-power consumption wearable biosensors. <br>
N-heterocyclic carbene (NHC) has been employed to functionalize the gold gate electrode, offering enhanced stability compared to thiol-based SAMs. For this purpose, we synthesized alkyne-modified NHC ligands, which can be functionalized with biomolecules through click chemistry. These ligands are subsequently integrated into the aerosol-jet printed gold gate electrode. These functionalized NHC gate electrodes were tested with both PEDOT:PSS and gNDI-Br2 OECT. An electrical signal change is observed with gNDI-Br2 OECTs when biotin and streptavidin are introduced to the NHC-Au functionalized gate electrodes. The enhanced stability of OECT biosensors, coupled with the adaptability of bioreceptors through click chemistry for gate electrode functionalization, offers promising potential for OECT-based biosensors. Furthermore, long-term stability measurements involving NHC-Au gate electrodes incubated for 24 months have demonstrated consistent performance, emphasizing the reliability and durability of these biosensors. <br>
In conclusion, this work highlights the synthesis and characterization of novel naphthalene diimide-based n-type small-molecule OMIECs, which are 3D printable. Using both drop-casting and AJP methods, we fabricate a gNDI-Br2 OECT that functions efficiently in accumulation mode, presenting high transconductance. Also, with thiol-based or NHC-based functionalization, the gNDI-Br2 OECT has demonstrated its efficacy as a flexible biosensor, specifically for SARS-CoV-2 detection. As such, gNDI-Br2 OMIEC plays a pivotal role in progressing small-molecule OMIEC development and n-type OECT biosensors, setting the stage for breakthroughs in low-power wearable healthcare applications. This type of OMIEC may also be beneficial for other organic electronics applications like photovoltaics, organic electrodes, and supercapacitors.</p>