Signal-on electrochemical aptasensor based on RGO-AuNPs and exonuclease-III with assistance of external probe for Hg2+ determination in shellfish

[Display omitted] •RGO-AuNPs is synthesized as a high-performance sensing platform for Hg2+ detection.•Exo-III is certified as a functional enzyme to accurately digest T-Hg2+-T structure.•DNA variations are sensitively recorded and amplified by an external signal probe.•The recommended results of this method are confidently proven with certified ICP-MS. In this work, a signal-on electrochemical aptasensor, based on RGO-AuNPs and exonuclease-III (Exo-III), is introduced for sensitive Hg2+ determination in shellfish. RGO-AuNPs is one-step electrodeposited on screen-printed electrode (SPE) surface as a high-performance sensing platform. Hg2+ aptamer serves as a molecular recognizer and selectively responds to Hg2+, thus triggering thymine-Hg2+-thymine (T-Hg2+-T) coordination. Exo-III is activated to cleavage the T-Hg2+-T structure, leading to partial aptamer breakage on sensor surface. Particularly, the reduction of DNA phosphate skeletons actuates is sensitively recorded by the external signal probe (I[Fe(CN)6]4-) and further amplified, thus composing a signal-on system. Under optimum conditions, as-fabricated sensor presents a good linear relationship to Hg2+ level in the range of 3.5×10−3 – 5.6×10−1 mg L−1, and the detection limit (LOD) is well found as 1.2×10−3 mg L−1. In certified ICP-MS and recovery tests of shellfish samples, the errors and recovery rates are calculated as 1.5%∼4.4% and 97.5%∼103.5%, respectively.