Pen-Writing Polypyrrole Arrays on Paper for Versatile Cheap Sensors

A simple and low-cost "pen-writing" method is exploited for integrating conducting polymer on cellulosic paper. The pen-written paper chip not only possesses excellent mechanical and electrical properties, but also serves as a versatile sensor, fulfilling several real-time and in situ detections for ammonia gas, thermal heating, and NIR light. The theoretical detection limit of ammonia gas can be as low as 1.2 ppm, which is a promising performance for industrial application. In addition, this "pen-writing" technique can be extended to generate wearable electrical textiles in a large scale.