Ink-Jet Printed Colorimetric Sensor for the Determination of Fe(II)

Ink-jet printing has been used to fabricate paper strips for the direct measurement of Fe(II) ions by means of a solid-state colorimetric assay. Toward this end, 2,2'-bipyridyl dye entrapped in a Nafion matrix was used and subsequently immobilized onto the paper strips. An apparatus for the simple readout of the paper strips, comprising a CMOS camera that allows to acquire Red, Green and Blue (RGB) colors and an image analysis software for data elaboration, has been also developed. The fabricated sensor has been tested for the determination of Fe(II) between 0 and 6 mM, allowing a lower detection limit of 50 μM. The paper sensor was rapid-<;5 min for the color development and color scanning. The printed paper strips were found stable, without any change in their sensitivity after storage for long periods. The developed sensor was successfully applied to the determination of iron(II) in pharmaceutical formulations.