A Turn-On Luminescence Method for Phosphate Determination Based on Fast Green-Functionalized ZrO:Yb,Er@ZrO Core@Shell Upconversion Nanoparticles.

The development of practical and sensitive tools for detecting phosphate deficiency could facilitate engineering approaches to enhance crop yield and quality in phosphate-stressed environments, reducing the misuse of nonrenewable fertilizers and their consequent ecological impact. Herein, a 975 nm-activated method based on ZrO:Yb,Er@ZrO core@shell upconversion nanoparticles is presented for rapid visualization and determination of the phosphate ions in aqueous solutions and extracts. At optimized thickness, the nondoped ZrO shell not only enhances the emission of the ZrO:Yb,Er but also provides an active surface for the intense interaction with the phosphate group, allowing a "label-free" determination that avoids the use of additional phosphate-recognizing elements like ligands or antibodies.