AuNPs enhanced electrochemical and optical dual-mode fiber optic sensor for trace Hg²⁺ detection

Efficient and low-concentration detection of heavy metal ions is crucial for healthcare and environmental monitoring. Traditional fiber optic surface plasmon resonance (SPR) sensors face challenges in detecting trace heavy metal ions due to limited sensitivity and the need for complex specific modifications. To overcome these challenges, an innovative electrochemical and optical dual-mode fiber optic sensor for in situ, real-time detection of trace mercury ions is proposed in this paper. The sensor utilizes a reflection-type fiber optic probe coated with thin gold (Au)/indium tin oxide (ITO) film and gold nanoparticles (AuNPs), enabling simultaneous electrochemical and optical interrogation. The coupling effect between the SPR of thin film and the localized surface plasmon resonance (LSPR) of AuNPs significantly improves optical sensitivity, with AuNPs also offering additional active sites for the redox reaction of Hg 2+ . The ITO film not only facilitates the stripping of Hg 2+ , leading to sharper stripping peaks but also enhances the ability of the sensor to rapidly respond to anomalous potential changes. Experimental results show that the sensor has a wide dynamic detection range from 10 −10 M to 10 −5 M, with a limit of detection reaching the pM level. The dual-mode functionality allows the simultaneous collection of voltage, current, and optical information, enabling cross-validation of the detection results and improving the accuracy and reliability of detection.