Poly(allylamine)-copper(II) coordination complex grafted on core@shell upconversion nanoparticles for ultrafast and sensitive determination of the phytohormone salicylic acid in plant extracts.

Salicylic acid (SA) is a phenolic phytohormone with critical roles in plant growth regulation and resistance to biotic and abiotic stress. Since low SA concentrations can modulate many plant biochemical responses, innovative analytical tools are required to deeply understand its activity and to control its exogenous application in modern agricultural systems. Herein, a NIR-activated composite based on NaYF