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Despite significant progress in solution‐processing of 2D materials, it remains challenging to reliably print high‐performance semiconducting channels that can be efficiently modulated in a field‐effect transistor (FET). Herein, electrochemically exfoliated MoS₂nanosheets are inkjet‐printed into ultrathin semiconducting channels, resulting in high on/off current ratios up to 10³. The reported printing strategy is reliable and general for thin film channel fabrication even in the presence of the ubiquitous coffee‐ring effect. Statistical modeling analysis on the printed pattern profiles suggests that a spaced parallel printing approach can overcome the coffee‐ring effect during inkjet printing, resulting in uniform 2D flake percolation networks. The uniformity of the printed features allows the MoS₂channel to be hundreds of micrometers long, which easily accommodates the typical inkjet printing resolution of tens of micrometers, thereby enabling fully printed FETs. As a proof of concept, FET water sensors are demonstrated using printed MoS₂as the FET channel, and printed graphene as the electrodes and the sensing area. After functionalization of the sensing area, the printed water sensor shows a selective response to Pb²⁺in water down to 2 ppb. This work paves the way for additive nanomanufacturing of FET‐based sensors and related devices using 2D nanomaterials.

 

Abstract Rapid, inexpensive, and easy-to-use coronavirus disease 2019 (COVID-19) home tests are key tools in addition to vaccines in the world wide fight to eliminate national and local shutdowns. However, currently available tests for SARS-CoV-2, the virus that causes COVID-19, are too expensive, painful, and irritating, or not sufficiently sensitive for routine, accurate home testing. Herein, we employ custom-formulated graphene inks and aerosol jet printing to create a rapid electrochemical immunosensor for direct detection of SARS-CoV-2 spike receptor-binding domain (RBD) in saliva samples acquired noninvasively. This sensor demonstrated limits of detection that are considerably lower than most commercial SARS-CoV-2 antigen tests (22.91 ± 4.72 pg ml −1 for spike RBD and 110.38 ± 9.00 pg ml −1 for spike S1) as well as fast response time (∼30 min), which was facilitated by the functionalization of printed graphene electrodes in a single-step with SARS-CoV-2 polyclonal antibody through the carbodiimide reaction without the need for nanoparticle functionalization or secondary antibody or metallic nanoparticle labels. This immunosensor presents a wide linear sensing range from 1 to 1000 ng ml −1 and does not react with other coexisting influenza viruses such as H1N1 hemagglutinin. By combining high-yield graphene ink synthesis, automated printing, high antigen selectivity, and rapid testing capability, this work offers a promising alternative to current SARS-CoV-2 antigen tests. 

Due to its excellent chemical/thermal stability and mechanical robustness, hexagonal boron nitride (hBN) is a promising solid matrix material for ionogels. While bulk hBN ionogels have been employed in macroscopic applications such as lithium-ion batteries, hBN ionogel inks that are compatible with high-resolution printing have not yet been realized. Here, we describe aerosol jet-printable ionogels using exfoliated hBN nanoplatelets as the solid matrix. The hBN nanoplatelets are produced from bulk hBN powders by liquid-phase exfoliation, allowing printable hBN ionogel inks to be formulated following the addition of an imidazolium ionic liquid and ethyl lactate. The resulting inks are reliably printed with variable patterns and controllable thicknesses by aerosol jet printing, resulting in hBN ionogels that possess high room-temperature ionic conductivities and storage moduli of >3 mS cm −1 and >1 MPa, respectively. By integrating the hBN ionogel with printed semiconductors and electrical contacts, fully-printed thin-film transistors with operating voltages below 1 V are demonstrated on polyimide films. These devices exhibit desirable electrical performance and robust mechanical tolerance against repeated bending cycles, thus confirming the suitability of hBN ionogels for printed and flexible electronics.