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A strategy has been devised for improving the quality of polyelectrolyte multilayers formed via the layer-by-layer technique. This strategy involves host–guest complexation of the pendant ions of a polyelectrolyte to reduce their affinity toward the pendant ions of a complementary polyelectrolyte. Evidence for the effectiveness of this approach has been obtained on the basis of film thickness, permeability, and surface roughness measurements of polyelectrolyte multilayers derived from poly(sodium 4-styrenesulfonate) and poly(diallyldimethyammonium chloride), using β-cyclodextrin as a host molecule.

In this paper, we designed a novel near-infrared aptamer-mediated fluorescence “turn off–on” nanosensor for highly sensitive and selective detection of kanamycin based on CuInS2 quantum dots (QDs)@graphene oxide (GO) nanocomposites. The carboxy groups on the surface of CuInS2 QDs (modified with mercaptopropionic acid) were conjugated with amino terminal kanamycin-binding Ky2 aptamer to form the Ky2-CuInS2 QDs in the presence of 1-(3-dimethylaminopropyl)-3-ethylcarbodiimide hydrochloride and N-hydroxysuccinimide. Then, the Ky2-CuInS2 QDs were facilely immobilized on the surface of GO through π–π stacking interaction between the nucleobases and GO, which caused the fluorescence of Ky2-CuInS2 QDs “turned off”. In the presence of kanamycin, the Ky2-CuInS2 QDs desorb from the surface of GO and bind to kanamycin with high affinity and specificity. As a result, the quenched fluorescence “turned on”. Under the optimum conditions, there was a good linear relationship between I/I0 (I and I0 were the fluorescence intensity of Ky2-CuInS2 QDs@GO in the presence and absence of kanamycin, respectively) and kanamycin concentration in the range of 0.3–45 nmol L−1 (0.174–26.1 μg L−1), with the detection limit of 0.12 nmol L−1 (0.070 μg L−1). The present nanosensor was utilized to detect kanamycin in the human serum, urine and milk samples with satisfactory results.