TFBG-SPR DNA-Biosensor for Renewable Ultra-Trace Detection of Mercury Ions

In this article, a tilted fiber Bragg grating (TFBG) plasmonic sensor based on thymine (T) - Hg - thymine (T) (T-Hg-T) base asymmetric pairing and Au nanoparticles (AuNPs), which can be used for highly sensitive and selective ultra-low-concentration Hg ²⁺ detection, has been demonstrated. As is known, TFBG can provide an effective mean to easily excite the surface plasmon resonance (SPR) phenomenon while the fiber is coated with metal layer. By measuring the evolution of spectra, the SPR properties hence the surface perturbation could be detected accurately. To achieve highly sensitive and selective Hg ²⁺ detection, the two specially designed single-strand probe DNAs (ssDNAs) with rich T base that can specifically forming stable T-Hg-T asymmetric pairing are served as a binding element for AuNPs labelled-target DNA conjugates. In the present of Hg ²⁺ , these two ssDNAs that modified respectively on the surface of the sensor and the AuNPs will create a double helix T-Hg-T structure between the two DNA oligonucleotides and result in the surface refractive index perturbation amplified by the AuNPs. To overcome the low reusability of the AuNPs based DNA biosensor, by using iodide ions that can form more stable compounds with mercury ions over the T-Hg ²⁺ -T structure, a regenerable DNA biosensor that can repeatedly detect mercury ions is developed. The experimental results demonstrate that this sensor shows an excellent ultra-low-concentration and selectivity detection capability for Hg ²⁺ with the limit of detection (LOD) of 3.073 × 10 ^-12 M (3.073 pM) as well as a large dynamic range of 8 order of magnitude from 1.0 × 10 ^-11 M to 1.0 × 10 ^-3 M simultaneously. Thus, the experimental results in various actual sample from ultrapure/tap water to even clinical human serum, also reveal that it has potential application for Hg ²⁺ detection in environmental samples and in clinic biological samples.