A nanopaper-based analytical device (NAD) is described for a colorimetric metal-complexing indicator-displacement assay (MIDA) for zoledronic acid (ZA). Bacterial cellulose nanopaper was doped with curcumin to obtain a chemosensor on which hydrophilic test zones were patterned via laser printing of hydrophobic walls. The color intensity of the test zones decreases in the presence of Fe(III) due to the formation of Fe(III)-curcumin complex. However, upon addition of ZA, Fe(III) ions preferably binds ZA. Subsequently, the color of the zone changes from light yellow to dark yellow. The changes in the absorption (measured at 427 nm) and of the color of the test stripe can be monitored visually, by using a digital camera, or by a spectrophotometer. Under optimal conditions, the analytical signals increase linearly in the 0.01–100 μM ZA concentration range, and the detection limits are 8.8 and 8.0 nM for smartphone and spectrophotometer-based methods, respectively. The method was employed to the determination of ZA in (spiked) urine, serum, saliva, and in pharmaceutical samples.
