An Ion-Competition Assisted Fiber Optic Plasmonic DNA Biosensing Platform for Iodide Detection

Iodine assays hold paramount significance in clinical diagnostics, thyroid hormone synthesis, and pharmaceutical advancements. DNA-based optical fiber biosensors have emerged as a pivotal platform for ion detection, leveraging their biocompatibility, specificity, and remarkable sensitivity. Due to the unique bonding characteristics of its bases, DNA probes can only form specific coordination structures with specific cations, posing challenges in clinical anion detection. Based on the principle of ion-competition binding abilities, this study proposes a new method for the highly selective detection of iodide ions (anion) by combining a programmed DNA probe with the tilted fiber Bragg grating surface plasmon resonance (TFBG-SPR) sensing technique. This method uses the asymmetric coordination structure formed between mercury ions and thymines to enable single-stranded DNA (ssDNA) probes to form a double helix, allowing for the decoration of AuNPs on the sensor surface. The interaction between iodide ions and mercury ions forms a stable complex, leading to the unwinding of the DNA double helix. This process leads to the detachment of AuNPs, bringing about a significant modulation of the sensor’s surface refractive index which is further extracted from the spectrum using an optimized demodulation method. Our method expands the application scope of TFBG-SPR-DNA biosensing by means of indirect detection, achieving high selectivity and rapid detection of iodide ions in anion analysis, while also offering a comprehensive solution for developing clinical point-of-care testing (POCT) ion detection platforms in the future.