Figure 1.

(A) Illustration of the fluorescence resonance energy transfer (FRET)-based sensor of lead ions using brilliant cresyl blue (BCB) molecules as fluorophores. (B) The principle of Pb²⁺ detection by GNR-based FRET assay. (C) Schematic illustration of a label-free fluorescent sensor for Hg²⁺ detection based on acridine orange and aptamer-wrapped gold nanoparticles. (D) Schematic illustration of the operating principle of the QD/DNA/AuNP ensemble sensor for Hg²⁺ detection. (A: Adapted from [76] with permission of The Royal Society of Chemistry, B: Adapted from [86] by permission of The Royal Society of Chemistry, C: Adapted from [88] by permission of The Royal Society of Chemistry, D: Adapted with permission from [92]. Copyright 2011 American Chemical Society)