Inkjet printing lanthanide doped nanorods test paper for visual assays of nitroaromatic explosives

The facile and sensitive strategies for detections of nitroaromatic explosives are highly desirable in many challenging environments, especially for homeland security against terrorism. Here, we inkjet printed polyethylenimine (PEI)-coated Ce, Tb co-doped NaGdF4 nanorods (NaGdF4:Ce/Tb NRs) onto common filter paper to construct test paper for visual and instant detections of a typical explosive 2,4,6-trinitrophenol (TNP). Polyethylenimine molecules not only facilitate the formation of uniform NaGdF4 nanorods but also provide specific recognized sites for TNP by the acid-base pairing interaction. The resultant TNP bound at the surface of PEI-coated NaGdF4:Ce/Tb NRs can strongly quench the phosphorescence with a remarkably high quenching constant by the charge transfer mechanism from NaGdF4:Ce/Tb NRs to TNP. By printing of the probe on a piece of filter paper, trace amounts of TNP can be visually detected by the appearance of a dark color against a bright green background under a UV lamp. This test paper can detect TNP as low as 0.45 ng mm(-2) by the naked eye, which provides a potential application in the rapid, on-line detections of explosives.