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While the efficiency of synthetic surfactants in controlling the dispersion behaviour of nanomaterials in aqueous solution has been well documented, issues on environmental impact remain unsolved. The aim of this study is to synthesize multi‐walled carbon nanotubes (MWCNTs) inks using green surfactants and their chemical, physical, and electrical performances are compared to those of synthetic surfactant inks. The conductive ink is synthesized by dispersing MWCNTs in surfactant solution (gum Arabic [GA], alkali lignin [AL], polyvinylpyrrolidone [PVP] or pluronic F‐127 [PL]) with various concentrations. Among four investigated surfactants, GA/MWCNTs and PVP/MWCNTs inks are selected for further investigation due to their excellent dispersion stability. The printability of both inks is assessed by analyzing the quality of the conductive patterns printed with different inkjet printers theoretically and experimentally. It is found that multi‐nozzle printer is capable of developing printed patterns with lower sheet resistance compared to single‐nozzle printer. Overall, 5 GA/MWCNTs ink recorded as the most stable ink with only 14.4% reduction of absorbance after 30 days and with zeta potential value of −40.3 ± 5.36 mV. Ten layers of 5 GA/MWCNTs ink printed on PVA demonstrate a dense MWCNTs networks, which contribute to the lowest surface resistance of 3.0 kΩ sq−1.

Simple tests of infectiousness that return results in minutes and directly from samples even with low viral loads could be a potential game-changer in the fight against COVID-19. Here, we describe an improved isothermal nucleic acid amplification assay, termed the RICCA (RNA Isothermal Co-assisted and Coupled Amplification) reaction, that consists of a simple one-pot format of ‘sample-in and result-out’ with a primary focus on the detection of low copy numbers of RNA virus directly from saliva without the need for laboratory processing. We demonstrate our assay by detecting 16S rRNA directly from E. coli cells with a sensitivity as low as 8 CFU/μL and RNA fragments from a synthetic template of SARS-CoV-2 with a sensitivity as low as 1740 copies/μL. We further demonstrate the applicability of our assay for real-time testing at the point of care by designing a closed format for paper-based lateral flow assay and detecting heat-inactivated SARS-COV-2 virus in human saliva at concentrations ranging from 28,000 to 2.8 copies/μL with a total assay time of 15–30 min.

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