Silver nanoclusters functionalized by chromotropic acid and layered double hydroxides for the turn-on detection of melamine

Abstract

This paper reports the fabrication of ultrathin films (UTFs) of silver nanoclusters functionalized by chromotropic acid (CTA) and layered double hydroxide nanosheets (CTA-AgNCs/LDH) via the layer-by-layer (LBL) assembly technique, and their fluorescence turn on response for the detection of melamine has been demonstrated. UV-vis absorption and fluorescence spectra show the uniform growth of the UTFs and the enhancement of interlayer CTA-AgNCs upon increasing the deposition cycle. The SEM image and XRD results indicate that the (CTA-AgNCs/LDH)_n UTFs possess long-range order stacking in the normal direction of the substrate, with CTA-AgNCs accommodated between the LDH nanosheets as a monolayer arrangement. Compared with CTA-AgNCs solution, the fluorescence intensity of UTFs has been improved significantly resulted from the localization and confinement effects of LDH nanosheets. Moreover, the (CTA-AgNCs/LDH)₁₀ displays sensor performance for melamine with a linear response range (0.03–0.1 μM), low detection limit (4 nM) and good stability. A high selectivity of UTFs toward melamine over the other amino acids, metal ions and some saccharides has also been demonstrated. The sensitive assay for melamine could be attributed to the interaction based on the recognition of triple hydrogen bonds between melamine and (CTA-AgNCs/LDH) films. Therefore, this work provides a convenient way to immobilize Ag nanoclusters using the LDH nanosheet as a 2D matrix, which has great potential for the development of melamine detection.