Non-invasive electrochemical sensing of toluidine blue in human saliva using silver conductive ink stabilized on paper substrate: A new platform in portable sensor technology

In this study, we developed a novel paper-based electrochemical microsensor for label-free TB detection using conducting silver nano-inks stabilized on the on the surface of photography paper. The silver ink stabilized on the surface of paper which maintained suitable conductivity and structural integrity after repeated bending, indicating excellent flexibility. In addition, the electrodes maintained stable conductivity (resistance of 5.2 Ω) and LED performance at 100 °C, indicating the thermal flexibility of the cellulose modified by ink due to the strong interaction of AgNPs with cellulose substrate. Also, exposure to moisture had minimal effect on the electrical properties, such that the brightness and LED resistance (1.7 Ω, ΔR = 2.7 Ω) remained stable, confirming the moisture resistance of the ink. The electrodes also dried immediately after drawing without requiring more time or temperatures, which was one of the advantages of our synthetic ink. The developed microscale sensor can accurately detect the concentration of salivary TB in the linear range of 10–1000 nM, with a lower limit of quantification of 10 nM, which is considered as suitable range for clinical and diagnostic applications.