A facile colorimetric assay for determination of salicylic acid in tobacco leaves using titanium dioxide nanoparticles

Abstract

A facile, colorimetric method for salicylic acid (SA) detection in tobacco leaves was developed using titanium dioxide nanoparticles (TiO₂ NPs). The sensing strategy is based on the reaction of TiO₂ NPs with SA at pH 5.5, which results in an intramolecular ligand to metal charge transfer transition between salicylate and Ti(IV) on the surface of TiO₂ NPs, and causes the TiO₂ NP solution to turn yellow. The TiO₂ NP probe exhibits high selectivity for SA over seven structural chemicals (4-hydroxybenzoic acid, 3-hydroxybenzoic acid, benzoic acid, acetylsalicylic acid, phenol, methyl salicylate, and jasmonic acid). Moreover, the difference in the absorbance of the TiO₂ NP solution is proportional to the concentration of SA over the range from 0.02 to 1.0 mM (R² = 0.992). By using the TiO₂ NP probe in 5 mM sodium acetate (pH 5.5) solutions, the limit of detection for SA was 15.4 μM at a signal-to-noise (S/N) ratio of 3. Furthermore, the practicality of the TiO₂ NP probe was validated for the determination of SA in tobacco leaves by demonstrating its advantages including simplicity and selectivity.