Dispersive liquid-liquid microextraction of trace Hg2+ for visual and fluorescence test

► DLLME-RBT method was developed for fast and visual detection of trace Hg2+. ► DLLME could yield >400-fold enrichment factor for Hg2+. ► RBT could offer visual and fluorescence detection for Hg2+. ► DLLME-RBT shown >1000-fold selectivity for Hg2+ to other ions. ► Hg2+ in deionized water, tap water and sea water was quantified.