Colorimetric and Photothermal Dual-modal Visual Detection of Iodide Ion Based on G-Quadruplex-Hemin Cascade Signal Amplification

The insufficient internal resorption of iodide ions (I⁻) leads to thyroid disorders, such as goiter, hypothyroidism, and cretinism in adults. In this paper, a portable point-of-care testing (POCT) platform was developed for the dual-modal analysis of I⁻, seamlessly integrating both colorimetric and photothermal thermometer techniques. The quantification of results was achieved using a standard thermometer or smartphone. G-Quadruplex/Hemin (G4/Hemin) is the DNAzyme with peroxidase-like activity. The catalytic efficacy of G-quadruplex structures can be enhanced with the help of I⁻, manifesting as multicolor transitions from colorless to green and then blue, and accompanied by the increase of temperature, which can be used for the quantitative detection of I⁻. Additionally, digital analysis according to the three-color channels (R/G/B) by a cellphone eliminated the requirement for intricate instruments. This dual-modal method for portable I⁻ determination is cost-effectiveness, simplicity, remarkable sensitivity (0.5 nmol/L) and selectivity. Besides, it was applied to determining the concentration of I⁻ in spiked serum samples.