Gold nanoparticles-enhanced hollow fiber surface plasmon resonance sensor for highly sensitive detection of mercury(ii) ions

Mercury(II) ions (Hg²⁺) are one of the most common and highly toxic heavy metal ions, which can contaminate the environment and damage the human health. Therefore, the precise detection of trace Hg²⁺ concentration is particularly important. Herein, gold nanoparticles-enhanced silver-coated hollow fiber (HF) surface plasmon resonance (SPR) sensor was developed for the highly sensitive detection of Hg²⁺ ions. Due to the inherent difficulty in directly detecting Hg²⁺ ions on the sensing surface, the advantages of gold nanoparticles (AuNPs) as signal amplification labels were exploited to improve the sensitivity of the sensor. In the presence of Hg²⁺ ions, we chemically modified the sensing silver film of the sensor with 4-mercaptopyridine (4-MPY) and 4-mercaptopyridine-functionalized gold nanoparticles (AuNPs/4-MPY). Owing to the specific coordination between Hg²⁺ and the nitrogen of pyridine, Hg²⁺ could be captured by 4-MPY to form a Hg(pyridine)₂ complex. After adsorption of the Hg²⁺ ions, the strong electromagnetic coupling between the AuNPs and the silver film led to a wavelength shift of the SPR resonance peak. Experiments for the detection of Hg²⁺ ions were performed in the concentration range of 5 nM to 1 μM to investigate the performance of the present sensor. The sensor achieved a limit of detection (LOD) as low as 5 nM. Moreover, the developed fiber sensor exhibited excellent performance in terms of sensitivity and repeatability. Our results show this strategy has widespread applications in the field of on-site heavy metal detection and biomedical monitoring.