Fluorescent sensing of ascorbic acid based on iodine induced oxidative etching and aggregation of lysozyme-templated silver nanoclusters.

In this work, we developed a sensitive and highly selective fluorescent approach for the detection of ascorbic acid (AA) by taking advantage of the oxidative etching effect of iodine (I2) on the lysozyme-stabilized silver nanoclusters (dLys-AgNCs) with fluorescence quenching. I2 could be produced from the redox reaction between iodate (IO3-) and AA, and thus the fluorescence intensity of dLys-AgNCs was turned off significantly in the coexistence of IO3- and AA. The fluorescence quenching of dLys-AgNCs had a good linear relationship with AA concentration, which allowed the detection of AA in the range from 0.05 to 45.0 μmol L-1 with a detection limit of 20 nmol L-1. The quenching mechanism was elucidated by Fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS), transmission electron microscopy (TEM), zeta potential, and dynamic light scattering (DLS) measurements, confirming that the fluorescence quenching of the dLys-AgNCs was attributed to the oxidative etching of the in situ generated I2, inducing aggregation of the dLys-AgNCs probe by forming Ag@AgI nanocomposite. The dLys-AgNCs probe exhibited excellent selectivity for AA sensing over several common reducing agents tested. Moreover, this approach was extended to the detection of AA in orange juice and urine with recovery rates in the range of 96.0% (RSD: 4.11) to 100.9% (RSD: 3.28) and 94.5% (RSD: 6.40) to 99.2% (RSD: 5.36), respectively.