Engineering ligand-free AgNPs for enhanced electrocatalytic detection of iodide via a dual-signal strategy

Due to the potential risks to human health posed by radioactive or abnormal levels of iodine, developing portable iodine sensors has received considerable attention. Herein, a novel dual-signal electrochemical sensor is constructed using ligand-free silver nanoparticles (lf-AgNPs) for portable iodide (I − ) detection. After effective removal of ligands, the obtained lf-AgNPs exhibit a significantly enhanced electrochemical response toward I − , with an 8.9-fold higher sensitivity compared to silver nanoparticles/carbon dots (AgNPs/CDs) over a wide concentration range of 0.9 μM to 1.4 mM and a limit of detection of 50 nM. The improvement is attributed to the accelerated electron transfer and increased active sites after ligand removal. Notably, a linear relationship between potential and the logarithm of I − concentration was established, enabling a complementary potentiometric sensing mode and forming the dual-signal strategy for I − detection. Mechanistic studies reveal that the increased active sites of Ag + on AgNPs can facilitate the catalytic oxidation of I − and lower the operating potential, thereby improving the anti-interference ability of the sensor, which can even be used for I − detection in saturated Cl − solution. Furthermore, the practicality of the sensor was demonstrated using screen-printed electrodes modified with lf-AgNPs, which enabled the effective and on-site I − detection in complex real samples (urine, river water, simulated seawater) with high reliability, reproducibility and stability. This work presents a low-cost ligand-removal strategy for constructing I − dual-signal electrochemical sensors with enhanced sensitivity and selectivity.