Ratiometric-enhanced G‑Quadruplex Probes for Amplified and Mix-to-Read Detection of Mercury Pollution in Aquatic Products

Mercury, as a global toxic pollutant, is easy to be accumulated in aquatic products and poses a great threat to human health. In this work, we proposed a mix-to-read, label-free, and robust assay for detecting mercury pollution in aquatic products by engineering a ratiometric-enhanced G-quadruplex probe. The transformation from the G-quadruplex to a hairpin-like structure allows us to confer a ratiometric and leveraged response to Hg2+, amplifying the signal-to-background ratio for Hg2+ detection. Hg2+ response was further improved by screening parallel- and antiparallel-, single-, and multiple-stranded G-quadruplex structures. Compared to the common aptamer probes, the ratiometric-enhanced G-quadruplex probe increased the sensitivity for Hg2+ detection by 4.7 times. This proposed sensing system allowed a simple and one-tube homogenous detection of Hg2+ at room temperature using a single unlabeled DNA sequence. Its application for Hg2+ detection in fish and shrimp conferred satisfactory recovery rates ranging from 98.5 to 105.9%. The label-free and mix-to-read assay is promising for the onsite detection of mercury pollution and facilitating food safety of aquatic products.