A reagent-loaded pencil, method of preparing a reagent-loaded pencil, and a system that uses reagent-loaded pencils are disclosed. The reagent-loaded pencil or pencils include a matrix of at least a soluble carrier, a hardening substance, and a reagent. The pencils also include a sheath disposed around at least a portion of the matrix. The soluble carrier may include poly(ethylene glycol) methyl ether. The hardening substance may leave a visible mark when abraded against a writing surface. One example of such a substance includes graphite. The sheath may be the outside of a wooden pencil or a mechanical pencil. A system that uses reagent-loaded pencils or compressed matrices may include a computer-controlled plotter that holds and plots with at least one of the reagent-loaded pencils or matrices.