▎ 摘　　要

Graphene oxide-rhodamine B hydrazide (GO-RhB) nanocomposite was prepared by a simple chemical method and characterized by various spectroscopic and analytical techniques. GO-RhB nanocomposite potentially detects Cr3+ ion (excitation/emission = 550 nm/572 nm) via fluorescence turn "on-off" approach. This composite showed high binding affinity (10(6) M-1) with Cr3+ and a+ limit of detection (LOD) down to picomolar concentration (LOD = 85.6 pM). As far as we know, this is the first report for the sensing of Cr3+ ion at picomolar concentration. GO-RhB selectively senses Cr3+ ion without any interference of other coexisting metal ions. In addition, this composite exhibited the dynamic nature of quenching in the presence of Cr3+ ion, which is confirmed by the Stern-Volmer plot, fluorescence temperature profiles, and decay time experiments. The GO-RhB nanocomposite-based fluorescent probe was successfully applied to the quantitative detection of Cr3+ ion in milk sample (linear range= 2 to 10 nM) with better performance than other existing methods. Besides, this GO-RhB composite showed better antibiofilm activity against Acinetobacter baumannii and methicillin-resistant Staphylococcus aureus (MRSA) by using the Congo red agar and tube method.