Screen printed carbon nanotube chemiresistive pH sensor on paper-based microfluidics

In this study, the authors presented a simple and cost-effective method for fabricating a carbon nanotubes (CNTs)-based paper-based sensing device via screen printing to determine solution pH. CNTs were chosen due to their high surface area and excellent mechanical and electrical properties, making them useful for various applications, including biological and chemical sensing. The paper-based device was fabricated using paper, a low-cost and accessible substrate, which also has a porous structure for capillary action. The hydrophobic and hydrophilic regions were established using wax printing and paper surface plasmon treatment to control the dimensions of the sensing channels. The CNTs ink was screen printed onto the paper, and the length and width of the sensing channels were controlled by the hydrophobic pattern design and mask design. The amount of CNTs printed was also easily controlled by varying the concentrations of the carbon ink. The resulting CNT-based films on paper were repeatedly produced with a homogeneous thickness. The fabricated sensors showed a linear response range from pH 3 to pH 10, with an optimal L/W ratio of 4, and an electrical signal was generated by measuring the channel resistance using conductive silver leads. This screen printing method provides a facile and low-cost approach for fabricating paper-based sensors that can be used for various sensing applications, including point-of-care diagnosis and environmental monitoring.