Ion sensing pencil: Draw your own sensor

We demonstrate for the first time the concept of ion sensing pencil (ISP). The pencil?s lead carries chemical sensing functionality and is constructed by compression of graphite and zeolite, while the clutch is prepared by 3D printing. The ISP can be used to draw a chemical sensor by simple abrasion onto a hydrophobic surface. The ISP can be stored at home, used immediately off-the-shelf without any handling prior to measurements. It?s simple preparation, handling, and measuring protocols offer the possibility of integration into large scale sensor networks or to be offered to the general public for use at home using readout devices already present at many homes. We demonstrate the chemical functionality of ISP by producing 14 ISPs prepared by compression of graphite and one of 14 different zeolites individually in 60:40 wt%. These ISPs are then used to draw electrodes which were characterized in analogy to ion-selective electrodes. The ISP-drawn electrodes were utilized as a multi-sensor array for the determination of water quality in a model sample, which is a first reported case of using zeolite-based electrodes in multisystem arrays, followed by the demonstration of their potential to be used by non-trained personnel. The implementation ISPs in potentiometric detection holds promise for further development of inexpensive and accessible tools for obtaining chemical information in areas where utilization of chemical sensors is currently limited.