Visual detection of ascorbic acid via alkyne-azide click reaction using gold nanoparticles as a colorimetric probe

An approach for visual sensing of ascorbic acid is presented. This method is based on the distance-dependent optical property of gold nanoparticles and the Cu(+)-catalyzed alkyne-azide click reaction. We prepared the terminal azide- and alkyne-functionalized gold nanoparticle probes. In the presence of Cu(2+), ascorbic acid could rapidly induce the aggregation of the functionalized gold nanoparticles, thereby resulting in a red-to-purple (or pink) color change. Ascorbic acid can be quantified visually or using a UV-vis spectrometer. The present limit of detection for ascorbic acid is 3 nM. This method exhibits excellent selectivity over other common organic reducing compounds (such as glucose, cysteine, dopamine, thiamine and uric acid). Without the aid of any advanced instruments, the assay of ascorbic acid could be performed with one step at room temperature. This method provides a potentially useful tool for the on-site detection of ascorbic acid.