Label-Free Single-Molecule Electrical Sensor for Ultrasensitive and Selective Detection of Iodide Ions in Human Urine.

Herein, a label-free single-molecule electrical sensor was first proposed for the ultrasensitive and selective detection of iodide ions in human urine. Single-molecule conductance measurements in different halogen ion solutions via scanning tunneling microscopy break junction (STM-BJ) clearly revealed that I ions strongly affect the stability and displacement distance (Δ) distribution of molecular junctions. Theoretical calculations prove that the specific adsorption of I ions modifies the surface properties and weakens the molecular adsorption. Furthermore, the average conductance peak area versus the logarithm of the I ion concentration has a very good linear relationship in the range of 5 × 10 to 5 × 10 M, with a correlation coefficient of 0.99. This quantitative analysis remains valid in the presence of interfering ions of SO, ClO, Br, and Cl as well as interfering molecules of ascorbic acid, uric acid, dopamine, and cysteine. A cross-comparison of the human urine detection results of this single-molecule electrical sensor with those of the clinical method of As-Ce catalytic spectrophotometry revealed an average difference of 0.9%, which decreased the detection time of 2 h with the traditional method to approximately 15 min. This work proves the promising practical potential of the single-molecule electrical technique for relevant clinical analysis.